EXPLAIN WHY EARTH’S EQUATORIAL REGIONS ARE NOT BECOMING WARMER, DESPITE THE FACT THAT THEY RECEIVE MORE INCOMING SOLAR RADIATION THAN THEY RADIATE BACK TO SPACE.

 EXPLAIN WHY EARTH’S EQUATORIAL REGIONS ARE NOT BECOMING WARMER, DESPITE THE FACT THAT THEY RECEIVE MORE INCOMING SOLAR RADIATION THAN THEY RADIATE BACK TO SPACE.

Hundreds of cars stranded on Chicago’s Lake Shore Drive on February 2, 2011, following
a winter blizzard of historic proportions. (AP Photo/ Kiichiro Sato)
After completing this chapter, you should be able to:
 Distinguish between weather and climate and name the basic elements of weather and climate.
 List several important atmospheric hazards and identify those that are storm related.
Hundreds of cars stranded on Chicago’s Lake Shore Drive on February 2, 2011, following
a winter blizzard of historic proportions. (AP Photo/ Kiichiro Sato)

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After completing this chapter, you should be able to:
 Distinguish between weather and climate and name the basic elements of weather and climate.
 List several important atmospheric hazards and identify those that are storm related.
 Construct a hypothesis and distinguish between a scientific hypothesis and a scientific
theory.
 List and describe Earth’s four major spheres.
 Define system and explain why Earth can be thought of as a system.
List the major gases composing Earth’s atmosphere and identify those components that are most
important meteorologically.
Explain why ozone depletion is a significant global issue.
Interpret a graph that shows changes in air pressure from Earth’s surface to the top of the atmosphere.
Sketch and label a graph showing the thermal structure of the atmosphere.
Distinguish between homosphere and heterosphere.
3
4 The Atmosphere: An Introduction to Meteorology Focus on the Atmosphere
everywhere on our planet. The United States likely has the greatest variety of weather of any country in
the world. Severe weather events, such as tornadoes, flash floods, and intense thunderstorms, as well as
hurricanes and bliz-zards, are collectively more frequent and more damaging in the United States than
in any other nation. Beyond its direct impact on the lives of individuals, the weather has a strong effect
on the world economy, by influencing agri- culture, energy use, water resources, transportation, and
industry.
Weather clearly influences our lives a great deal. Yet it is also important to realize that people influence
the atmo-sphere and its behavior as well (Figure 1–2). There are, and will continue to be, significant
political and scientific deci-sions to make involving these impacts. Answers to ques-tions regarding air
pollution and its control and the effects of various emissions on global climate are important exam- ples.
So there is a need for increased awareness and under-standing of our atmosphere and its behavior.
Meteorology, Weather, and Climate
The subtitle of this book includes the word meteorology. Meteorology is the scientific study of the
atmosphere and the phenomena that we usually refer to as weather. Along with geology, oceanography,
and astronomy, meteorology is considered one of the Earth sciences—the sciences that seek to
understand our planet. It is important to point out that there are not strict boundaries among the Earth sciences; in many situations, these sciences overlap. Moreover, all of the Earth sciences involve an
understanding and applica-tion of knowledge and principles from physics, chemistry, and biology. You
will see many examples of this fact in your study of meteorology.
Acted on by the combined effects of Earth’s motions and energy from the Sun, our planet’s formless and
invis- ible envelope of air reacts by producing an infinite variety of weather, which in turn creates the
basic pattern of global climates. Although not identical, weather and climate have much in common.
Weather is constantly changing, sometimes from hour to hour and at other times from day to day. It is a
term that refers to the state of the atmosphere at a given time and place. Whereas changes in the
weather are continuous and sometimes seemingly erratic, it is nevertheless possible to arrive at a
generalization of these variations. Such a descrip-tion of aggregate weather conditions is termed
climate. It is based on observations that have been accumulated over many decades. Climate is often
defined simply as “average weather,” but this is an inadequate definition. In order to accurately portray
the character of an area, variations and extremes must also be included, as well as the probabili-ties
that such departures will take place. For example, it is necessary for farmers to know the average rainfall
during the growing season, and it is also important to know the frequency of extremely wet and
extremely dry years. Thus, climate is the sum of all statistical weather information that helps describe a
place or region.
ATMOSPHERE
Introduction to the Atmosphere ▸Weather and Climate
Weather influences our everyday activities, our jobs, and our health and comfort. Many of us pay little
attention to the weather unless we are inconvenienced by it or when it adds to our enjoyment of
outdoor activities. Nevertheless, there are few other aspects of our physical environment that affect our
lives more than the phenomena we collectively call the weather.
Weather in the United States
The United States occupies an area that stretches from the tropics to the Arctic Circle. It has thousands
of miles of coast- line and extensive regions that are far from the influence of the ocean. Some
landscapes are mountainous, and others are dominated by plains. It is a place where Pacific storms
strike the West Coast, while the East is sometimes influenced by events in the Atlantic and the Gulf of
Mexico. For those in the center of the country, it is common to experience weather events triggered
when frigid southward-bound Canadian air masses clash with northward-moving tropical ones from the
Gulf of Mexico.
Stories about weather are a routine part of the daily news. Articles and items about the effects of heat,
cold, floods, drought, fog, snow, ice, and strong winds are com-monplace (Figure 1–1). Memorable
weather events occur Figure1–1 Fewaspectsofourphysicalenvironmentinfluence our daily lives more than the weather.
Tornadoes are intense and destructive local storms of short duration that cause an average of about 55
deaths each year. (Photo by Wave RF/Photolibrary)
Chapter 1 Introduction to the Atmosphere 5
(a) (b)
Figure 1–2 These examples remind us that people influence the atmosphere and its behavior.
(a) Motor vehicles are a significant contributor to air pollution. This traffic jam was in Kuala Lumpur,
Malaysia. (Photo by Ron Yue/Alamy) (b) Smoke bellows from a coal-fired electricity-generating plant in
New Delhi, India, in June 2008. (AP Photo/Gurindes Osan)
Maps similar to the one in Figure 1–3 are familiar to everyone who checks the weather report in the
morning newspaper or on a television station. In addition to showing predicted high temperatures for
the day, this map shows other basic weather information about cloud cover, precipi-tation, and fronts.
Suppose you were planning a vacation trip to an unfa- miliar place. You would probably want to know
what kind of weather to expect. Such information would help as you selected clothes to pack and could
influence decisions regarding activities you might engage in during your stay. Unfortunately, weather
forecasts that go beyond a few days are not very dependable. Thus, it would not be possible to get a
reliable weather report about the conditions you are likely to encounter during your vacation.
Instead, you might ask someone who is familiar with the area about what kind of weather to expect.
“Are
thunderstorms common?” “Does it get cold at night?” “Are the afternoons sunny?” What you are
seeking is information about the climate, the conditions that are typical for that
Students Sometimes Ask …
Does meteorology have anything to do with meteors?
Yes, there is a connection. Most people use the word meteor when referring to solid particles
(meteoroids) that enter Earth’s atmosphere from space and “burn up” due to friction (“shooting stars”).
The term meteorology was coined in 340 BC, when the Greek philosopher Aristotle wrote a book titled
Meteorlogica, which included explanations of atmospheric and astronomical phenomena. In Aristotle’s
day anything that fell from or was seen in the sky was called a meteor. Today we distinguish between
particles of ice or water in the atmosphere (called hydrometeors) and extraterrestrial objects called
meteoroids, or meteors.
6
The Atmosphere: An Introduction to Meteorology
30s 20s H
10s 40s
50s
–0s
50s
cannot predict the weather. Although the place may usually (climatically) be warm, sunny, and dry
during the time of your planned vacation, you may actually experience cool, over- cast, and rainy
weather. There is a well-known saying that summarizes this idea: “Climate is what you expect, but
weather is what you get.”
The nature of both weather and cli-mate is expressed in terms of the same basic elements—those
quantities or properties that are measured regu- larly. The most important are (1) the temperature of
the air, (2) the humid- ity of the air, (3) the type and amount of cloudiness, (4) the type and amount of
precipitation, (5) the pressure exert- ed by the air, and (6) the speed and direction of the wind. These
elements constitute the variables by which weather patterns and climate types are depicted. Although
you will study these elements separately at first, keep in mind that they are very much inter-
0s
L
0s 20s
H
20s 0s
10s
50s
60s
–10s
Rain T-storm Snow Ice
place. Another useful source of such information is the great variety of climate tables, maps, and graphs
that are available. For example, the map in Figure 1–4 shows the average per- centage of possible
sunshine in the United States for the month of November, and the graph in Figure 1–5 shows average
daily high and low temperatures for each month, as well as extremes, for New York City.
Such information could, no doubt, help as you planned your trip. But it is important to realize that
climate data –0s
30s
40s 10s 70sH
20s
40s
A typical newspaper weather map for a day in late December. The color bands show the high
temperatures forecast for the day.
Figure 1–3
30 40
50 60
70
80 90
30
30 40
30 40
50
60
90
80
70 60
Figure 1–4 Mean percentage of possible sunshine for November. Southern Arizona is clearly the
sunniest area. By contrast, parts of the Pacific Northwest receive a much smaller percentage of the
possible sunshine. Climate maps such as this one are based on many years of data.
30s
50s
80s
Mostly cloudy
40 Mostly sunny
Partly cloudy
60
related. A change in one of the elements often produces changes in the others.
Concept Check 1.1
1 Distinguish among meteorology, weather, and climate.
2 List the basic elements of weather and climate.
48
44
40
36
32 90 28
ger price tag.
Between 1980 and 2010 the United States experienced
99 weather-related disasters in which overall damages
Chapter 1 Introduction to the Atmosphere 7

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by all other weather events combined. Moreover, although
severe storms and floods usually generate more attention, 110 droughts can be just as devastating and
carry an even bigRecord
daily
Av
dail
highs
erage
y highs
Average
dai
ly lows Record daily lows
100
24 20
and costs reached or exceeded $1 billion (Figure 1–7). The 80 combined costs of these events exceeded
$725 billion (nor-
70
malized to 2007 dollars)! During the decade 1999–2008, an average of 629 direct weather fatalities
occurred per year in the United States. During this span, the annual economic impacts of adverse
weather on the national highway system alone exceeded $40 billion, and weather-related air traffic
delays caused $4.2 billion in annual losses.
16 60
12 8 4 0
50
40
At appropriate places throughout this book, you will Two entire chapters (Chapter 10 and Chapter 11)
focus
This is a scene on a day in late April in southern Arizona’s Organ Pipe Cactus National Monument. (Photo
by Michael Collier)
Question 1 Write two brief statements about the locale in this image—one that relates to weather and
one that relates to climate.
30 have an opportunity to learn about atmospheric hazards.
–4
–8
–12 10 –16
–20
– 24 –28 –32
20
0 –10 –20
JFMAMJJASOND Month Figure 1–5 Graph showing daily temperature data for New York City. In addition to the average daily
maximum and minimum temperatures for each month, extremes are also shown. As this graph shows,
there can be significant departures from the average.
Atmospheric Hazards: Assault by the Elements
Natural hazards are a part of living on Earth. Every day they adversely affect literally millions of people
worldwide and are responsible for staggering damages. Some, such as earthquakes and volcanic
eruptions, are geological. Many others are related to the atmosphere.
Occurrences of severe weather are far more fascinating than ordinary weather phenomena. A
spectacular light- ning display generated by a severe thunderstorm can elicit both awe and fear ( Figure
1–6a). Of course, hurricanes and tornadoes attract a great deal of much-deserved attention. A single
tornado outbreak or hurricane can cause billions of dollars in property damage, much human suffering,
and many deaths.
Of course, other atmospheric hazards adversely affect us. Some are storm related, such as blizzards, hail,
and freezing rain. Others are not direct results of storms. Heat waves, cold waves, fog, wildfires, and
drought are impor-tant examples (Figure 1–6b). In some years the loss of human life due to excessive
heat or bitter cold exceeds that caused
Temperature ( ̊C)
Temperature ( ̊F)
8 The Atmosphere: An Introduction to Meteorology
(a)
(b)
Figure 1–6 (a) Many people have incorrect perceptions of weather dangers and are unaware of the
relative differences of weather threats to human life. For example, they are awed by
the threat of hurricanes and tornadoes and plan accordingly on how to respond (for example, “Tornado
Awareness Week” each spring) but fail to realize that lightning and winter storms can be greater threats.
(Photo by Mark Newman/Superstock) (b) During the summer, dry weather coupled with lightning and
strong winds contribute to wildfire danger. Millions of acres are burned each year, especially in the West.
The loss of anchoring vegetation sets the stage for accelerated erosion when heavy rains subsequently
occur. Near Boulder, Colorado, October 10, 2010. (AP Photo/ The Daily Camera, Paul Aiken)
The Nature
of Scientific Inquiry
As members of a modern society, we are constantly reminded of the benefits derived from science. But
what exactly is the nature of scientific inquiry? Developing an understanding of how science is done and
how scientists work is an impor-tant theme in this book. You will explore the difficulties of gathering data and some of the ingenious methods that have been developed to overcome these difficulties. You
will also
almost entirely on hazardous weather. In addition, a number of the book’s special-interest boxes are
devoted to a broad variety of severe and hazardous weather, including heat waves, winter storms,
floods, dust storms, drought, mudflows, and lightning.
Every day our planet experiences an incredible assault by the atmosphere, so it is important to develop
an aware- ness and understanding of these significant weather events.
Concept Check 1.2
1 List at least five storm-related atmospheric hazards.
2 What are three atmospheric hazards that are not directly storm related?
916 892
Chapter 1 Introduction to the Atmosphere 9 Hypothesis
Once facts have been gathered and principles have been formulated to describe a natural phenomenon,
investigators try to explain
2
1
1
1
1
9
7
4
2
768howorwhythingshappeninthemanner observed. They often do this by construct-
644ingatentative(oruntested)explanation, which is called a scientific hypothesis. It is
520bestifaninvestigatorcanformulatemore than one hypothesis to explain a given set of
46observations.Ifanindividualscientistisun- able to devise multiple hypotheses, others in the scientific
community will almost always develop alternative explanations. A spirited debate frequently ensues. As
a result, exten-sive research is conducted by proponents of opposing hypotheses, and the results are
made available to the wider scientific com-
32 28 14 00
munity in scientific journals.
Before a hypothesis can become an
accepted part of scientific knowledge, it must pass objective testing and analysis. If a hypothesis cannot
be tested, it is not scientifically useful, no matter how in-teresting it might seem. The verification process requires that predictions be made based on the hypothesis being considered and the predictions
be tested by being compared against objective observations
Year
Between 1980 and 2010 the United States experienced 99 weather-related disasters in which overall
damages and costs reached or exceeded $1 billion. This bar graph shows the number of events that
occurred each year and the damage amounts in billions of dollars (normalized to 2007 dollars). The total
losses for the
99 events exceeded $725 billion! For more about these extraordinary events see
www.ncdc.noaa.gov/oa/reports/billionz.html. (After NOAA)
Figure 1–7
see examples of how hypotheses are formulated and tested, as well as learn about the development of
some significant scientific theories.
All science is based on the assumption that the natu-ral world behaves in a consistent and predictable
manner that is comprehensible through careful, systematic study. The overall goal of science is to
discover the underly- ing patterns in nature and then to use this knowledge to make predictions about
what should or should not be expected, given certain facts or circumstances. For example, by
understanding the processes and condi-tions that produce certain cloud types, meteorologists are often
able to predict the approximate time and place of their formation.
The development of new scientific knowledge involves some basic logical processes that are universally
accepted. To determine what is occurring in the natural world, sci- entists collect scientific facts through
observation and measurement. The types of facts that are collected often seek to answer a well-defined
question about the natural world, such as “Why does fog frequently develop in this place?” or “What
causes rain to form in this cloud type?” Because some error is inevitable, the accuracy of a particu- lar
measurement or observation is always open to question. Nevertheless, these data are essential to
science and serve as a springboard for the development of scientific theories (Box 1–1).
of nature. Put another way, hypotheses must fit observa-tions other than those used to formulate them
in the first place. Hypotheses that fail rigorous testing are ultimately discarded. The history of science is
littered with discarded hypotheses. One of the best known is the Earth-centered model of the
universe—a proposal that was supported by the apparent daily motion of the Sun, Moon, and stars
around Earth.
Theory
When a hypothesis has survived extensive scrutiny and when competing ones have been eliminated, a
hypothesis may be elevated to the status of a scientific theory. In ev- eryday language we may say,
“That’s only a theory.” But a scientific theory is a well-tested and widely accepted view that the scientific
community agrees best explains certain observable facts. Some theories that are extensively documented and extremely well supported are comprehensive in
scope. An example from the Earth sciences is the theory of plate tec-tonics, which provides the
framework for understanding the origin of mountains, earthquakes, and volcanic activity. It also explains
the evolution of continents and ocean basins through time. As you will see in Chapter 14, this theory
also helps us understand some important aspects of climate change through long spans of geologic time.
1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
Number of events
Damage amounts in billions of dollars
10 The Atmosphere: An Introduction to Meteorology
Box 1–1 Monitoring Earth from Space
Scientific facts are gathered in many ways, including through laboratory experiments and field
observations and measurements. Satellites provide another very important source of data. Satellite
images give us perspectives that are difficult to gain from more traditional sources (Figure 1–A).
Moreover, the high-tech instruments aboard many satellites enable scientists to gather information
from remote regions where data are otherwise scarce.
The image in Figure 1–B is from NASA’s Tropical Rainfall Measuring Mission (TRMM). TRMM is a
research satellite designed to expand our understanding of Earth’s water (hydrologic) cycle and its role
in our climate system. By covering the region between
the latitudes 35° north and 35° south, it provides much-needed data on rainfall and the heat release
associated with rainfall. Many types of measurements and images are possible. Instruments aboard the
TRMM satellite have greatly expanded our ability to collect precipitation data. In addition to recording
data for land areas, this satellite provides extremely precise measurements of rainfall over the oceans
where conventional land-based instruments cannot see. This
is especially important because much of Earth’s rain falls in ocean-covered tropical areas, and a great
deal of the globe’s weather-producing energy comes from
heat exchanges involved in the rainfall process. Until the TRMM, information on
the intensity and amount of rainfall over the tropics was scanty. Such data are crucial to understanding
and predicting global climate change.
FIGURE 1–B This map of rainfall for December 7–13, 2004, in Malaysia was constructed using TRMM
data. Over 800 millimeters (32 inches) of rain fell along the east coast of the peninsula (darkest red area).
The extraordinary rains caused extensive flooding and triggered many mudflows. (NASA/TRMM image)
Scientific Methods The processes just described, in which scientists gather facts through observations and formulate
scientific hypotheses and theories, is called the scientific method. Contrary to popu- lar belief, the
scientific method is not a standard recipe that scientists apply in a routine manner to unravel the secrets
of our natural world. Rather, it is an endeavor that involves creativity and insight. Rutherford and
Ahlgren put it this
FIGURE 1–A Satellite image of a massive winter storm on February 1, 2011. During a winter marked by
several crippling storms, this one stands out. Heavy snow, ice, freezing rain, and frigid winds battered
nearly two-thirds of the contiguous United States. In this image, the storm measures about 2000
kilometers (1240 miles) across. Satellites allow us to monitor the development and movement of major
weather systems. (NASA)
Sumatra
7.9 200
Malaysia
15.7 23.6 31.5 Inches 400 600 800 mm
way: “Inventing hypotheses or theories to imagine how the world works and then figuring out how they
can be put to the test of reality is as creative as writing poetry, composing music, or designing
skyscrapers.”*
*F. James Rutherford and Andrew Ahlgren, Science for All Americans (New York: Oxford University Press,
1990), p. 7.
Singapore
There is not a fixed path that scientists always follow that leads unerringly to scientific knowledge.
Nevertheless, many scientific investigations involve the following steps: (1) A question is raised about
the natural world; (2) scientific data are collected that relate to the question (Figure 1–8); (3) questions
are posed that relate to the data, and one or more working hypotheses are developed that may answer
these questions; (4) observations and experiments are devel- oped to test the hypotheses; (5) the
hypotheses are accepted, modified, or rejected, based on extensive testing; (6) data and results are
shared with the scientific community for critical and further testing.
Other scientific discoveries may result from purely theoretical ideas that stand up to extensive
examination. Some researchers use high-speed computers to simulate what is happening in the “real”
world. These models are useful when dealing with natural processes that occur on very long time scales
or take place in extreme or inacces-sible locations. Still other scientific advancements have been made
when a totally unexpected happening occurred during an experiment. These serendipitous discoveries
are more than pure luck; as Louis Pasteur stated, “In the field of observation, chance favors only the
prepared mind.” Scientific knowledge is acquired through several ave- nues, so it might be best to describe the nature of
scientific
Chapter 1 Introduction to the Atmosphere 11 Students Sometimes Ask…
In class you compared a hypothesis to a theory. How is each one different from a scientific law?
A scientific law is a basic principle that describes a particular behavior of nature that is generally narrow
in scope and can be stated briefly—often as a simple mathematical equation. Because scientific laws
have been shown time and time again to be consistent with observations and measurements, they are
rarely discarded. Laws may, however, require modifications to fit new findings. For example, Newton’s
laws of motion are still useful
for everyday applications (NASA uses them to calculate satellite trajectories), but they do not work at
velocities approaching the speed of light. For these circumstances, they have been supplanted by
Einstein’s theory of relativity.
inquiry as the methods of science rather than the scientific method. In addition, it should always be
remembered that even the most compelling scientific theories are still simpli- fied explanations of the
natural world.
Concept Check 1.3
1 How is a scientific hypothesis different from a scientific
theory?
2 List the basic steps followed in many scientific investigations.
Figure 1–8 Gathering data and making careful observations
are a basic part of scientific inquiry. (a) This Automated Surface Observing System (ASOS) installation is
one of nearly 900 in use for data gathering as part of the U.S. primary surface observing network. (Photo
by Bobbé Christopherson) (b) These scientists are working with a sediment core recovered from the
ocean floor. Such cores often contain useful data about Earth’s climate history. (Photo by Science
Source/Photo Researchers, Inc.)
(a)
(b)
12 The Atmosphere: An Introduction to Meteorology Students Sometimes Ask…
Who provides all the data needed to prepare
a weather forecast?
Data from every part of the globe are needed to produce accurate weather forecasts. The World
Meteorological Organization (WMO) was established by the United Nations to coordinate scientific
activity related to weather and climate. It consists of 187 member states and territories, representing all parts of the globe. Its World Weather Watch provides up-to-the-minute standardized observations
through member-operated observation systems. This global system involves more than 15 satellites,
10,000 land- observation and 7300 ship stations, hundreds of automated data buoys, and thousands of
aircraft.
Earth’s Spheres
The images in Figure 1–9 are considered to be classics be- cause they let humanity see Earth differently
than ever be- fore. Figure 1–9a, known as “Earthrise,” was taken when the Apollo 8 astronauts orbited
the Moon for the first time in December 1968. As the spacecraft rounded the Moon, Earth appeared to
rise above the lunar surface. Figure 1–9b, referred to as “The Blue Marble,” is perhaps the most widely
reproduced image of Earth; it was taken in December 1972 by the crew of Apollo 17 during the last
manned lunar mis-sion. These early views profoundly altered our conceptual- izations of Earth and
remain powerful images decades after they were first viewed. Seen from space, Earth is breathtak- ing
in its beauty and startling in its solitude. The photos remind us that our home is, after all, a planet—
small, self- contained, and in some ways even fragile. Bill Anders, the
Apollo 8 astronaut who took the “Earthrise” photo, expressed it this way: “We came all this way to
explore the Moon, and the most important thing is that we discovered the Earth.”
As we look closely at our planet from space, it becomes apparent that Earth is much more than rock and
soil. In fact, the most conspicuous features in Figure 1–9a are not continents but swirling clouds
suspended above the sur- face of the vast global ocean. These features emphasize the importance of
water on our planet.
The closer view of Earth from space shown in Figure 1–9b helps us appreciate why the physical
environment is tradi-tionally divided into three major parts: the solid Earth, the water portion of our
planet, and Earth’s gaseous envelope.
It should be emphasized that our environment is highly integrated and is not dominated by rock, water,
or air alone. It is instead characterized by continuous interactions as air comes in contact with rock, rock
with water, and water with air. Moreover, the biosphere, the totality of life forms on our planet, extends
into each of the three physical realms and is an equally integral part of the planet.
The interactions among Earth’s four spheres are incal- culable. Figure 1–10 provides us with one easy-tovisualize
example. The shoreline is an obvious meeting place for rock, water, and air. In this scene, ocean
waves that were created by the drag of air moving across the water are breaking against the rocky shore.
The force of the water can be powerful, and the erosional work that is accomplished can be great.
On a human scale Earth is huge. Its surface area occu- pies 500,000,000 square kilometers (193 million
square miles). We divide this vast planet into four independent parts. Because each part loosely
occupies a shell around Earth, we call them spheres. The four spheres include the geosphere (solid
Earth), the atmosphere (gaseous envelope), the hydrosphere (water portion), and the biosphere (life). Figure 1–9 (a) View, called “Earthrise,” that greeted the Apollo 8 astronauts as their spacecraft emerged
from behind the Moon. (NASA) (b) Africa and Arabia are prominent in this classic image called “The Blue
Marble” taken from Apollo 17. The tan cloud-free zones over the land coincide with major desert
regions. The band of clouds across central Africa is associated with a much wetter climate that in places
sustains tropical rain forests. The dark blue of the oceans and the swirling cloud patterns remind us of
the importance of the oceans and the atmosphere. Antarctica, a continent covered by glacial ice, is
visible at the South Pole. (NASA)
(a) (b)
Figure 1–10 The shoreline is one obvious example of an interface—a common boundary where different
parts of a system interact. In this scene, ocean waves (hydrosphere) that were created by the force of
moving air (atmosphere) break against a rocky shore (geosphere). (Photo by Radius Images/
photolibrary.com)
It is important to remember that these spheres are not separated by well-defined boundaries; rather,
each sphere is intertwined with all of the others. In addition, each of Earth’s four major spheres can be
thought of as being com- posed of numerous interrelated parts.
The Geosphere
Beneath the atmosphere and the ocean is the solid Earth, or geosphere. The geosphere extends from
the surface to the center of the planet, a depth of about 6400 kilometers (nearly 4000 miles), making it
by far the largest of Earth’s four spheres.
Based on compositional differences, the geosphere is divided into three principal regions: the dense
inner sphere, called the core; the less dense mantle; and the crust, which is the light and very thin outer
skin of Earth.
Soil, the thin veneer of material at Earth’s surface that supports the growth of plants, may be thought of
as part of all four spheres. The solid portion is a mixture of weathered rock debris (geosphere) and
organic matter from decayed plant and animal life (biosphere). The decomposed and dis- integrated
rock debris is the product of weathering process-es that require air (atmosphere) and water
(hydrosphere). Air and water also occupy the open spaces between the solid particles.
The Atmosphere
Earth is surrounded by a life-giving gaseous envelope called the atmosphere (Figure 1–11). When we
watch a high-flying jet plane cross the sky, it seems that the atmosphere extends upward for a great
distance. However, when compared to the thickness (radius) of the solid Earth (about 6400 kilome -ters
[4000 miles]), the atmosphere is a very shallow layer. More than 99 percent of the atmosphere is within
30 kilome-ters (20 miles) of Earth’s surface. This thin blanket of air is nevertheless an integral part of
the planet. It not only pro- vides the air that we breathe but also acts to protect us from the dangerous
radiation emitted by the Sun. The energy exchanges that continually occur between the atmosphere and
Earth’s surface and between the atmosphere and space produce the effects we call weather. If, like the Moon, Earth had no atmosphere, our planet would not only be lifeless, but many of the processes and
interactions that make the surface such a dynamic place could not operate.
The Hydrosphere
Earth is sometimes called the blue planet. More than any-thing else, water makes Earth unique. The
hydrosphere is a dynamic mass that is continually on the move, evapo-rating from the oceans to the
atmosphere, precipitating to
Chapter 1 Introduction to the Atmosphere 13
14
The Atmosphere: An Introduction to Meteorology
160 140 120 100
80 60 40 20
Noctilucent clouds
Top of troposphere
Figure 1–11 This unique image of Earth’s atmosphere merging with the emptiness
of space resembles an abstract painting.
It was taken in June 2007 by a Space Shuttle crew member. The silvery streaks (called noctilucent clouds)
high in the blue area are at a height of about 80 kilometers (50 miles). Air pressure at this height is less
than one-thousandth of that at sea level.
The reddish zone in the lower portion of the image is the densest part of the atmosphere. It is here, in a
layer called the troposphere, that practically all weather phenomena occur. Ninety percent of Earth’s
atmosphere occurs within just 16 kilometers (10 miles) of the surface. (NASA)
(2.5 miles) and in boiling hot springs. Moreover, air currents can carry microorganisms many kilometers
into the atmo- sphere. But even when we consider these extremes, life still must be thought of as being
confined to a narrow band very near Earth’s surface.
Plants and animals depend on the physical environ- ment for the basics of life. However, organisms do
more than just respond to their physical environment. Through
Earth’s surface
the land, and running back to the ocean again. The global ocean is certainly the most prominent feature
of the hydro-sphere, blanketing nearly 71 percent of Earth’s surface to an average depth of about 3800
meters (12,500 feet). It accounts for about 97 percent of Earth’s water (Figure 1–12). How- ever, the hydrosphere also includes the fresh water found in clouds, streams, lakes, and glaciers, as we ll as that
found underground.
Although these latter sources consti-tute just a tiny fraction of the total, they are much more important
than their meager percentage indicates. Clouds, of course, play a vital role in many weath- er and
climate processes. In addition to providing the fresh water that is so vital to life on land, streams,
glaciers, and groundwater are responsible for sculpt- ing and creating many of our planet’s varied
landforms.
The Biosphere
The biosphere includes all life on Earth (Figure 1–13). Ocean life is concentrated in the sunlit surface
waters of the sea. Most life on land is also concentrated near the surface, with tree roots and burrowing
animals reaching a few me-ters underground and flying insects and birds reaching a kilometer or so
above the surface. A surprising variety of life forms are also adapted to extreme en- vironments. For
example, on the ocean floor, where pressures are extreme and no light penetrates, there are places
where vents spew hot, mineral-rich fluids that support communities of ex- otic life-forms. On land, some
bacteria thrive in rocks as deep as 4 kilometers
Oceans 97.2%
Hydrosphere
2.8%
Glaciers 2.15%
Freshwater lakes 0.009% Saline lakes and inland seas 0.008%
Soil moisture 0.005% Atmosphere 0.001% Stream channels 0.0001%
Groundwater 0.62%
Stream channel
Glaciers
Groundwater (spring)
Nonocean Component (% of total hydrosphere)
Figure1–12 DistributionofEarth’swater.Obviously,mostofEarth’swaterisintheoceans. Glacial ice
represents about 85 percent of all the water outside the oceans. When only liquid freshwater is
considered, more than 90 percent is groundwater. (Glacier photo by Bernhard Edmaier/Photo
Researchers, Inc.; stream photo by E.J. Tarbuck; and groundwater photo by Michael Collier)
Altitude in kilometers (km)
Chapter 1 Introduction to the Atmosphere 15 (a)
countless interactions, life forms help maintain and alter their physical environment. Without life, the
makeup and nature of the geosphere, hydrosphere, and atmosphere would be very different.
Concept Check 1.4
 1 Compare the height of the atmosphere to the
 thickness of the geosphere.
 2 How much of Earth’s surface do oceans cover?
 3 How much of the planet’s total water supply do the oceans represent?
 4 List and briefly define the four spheres that constitute our environment.
Earth as a System
Anyone who studies Earth soon learns that our planet is a dynamic body with many separate but highly
interactive parts, or spheres. The atmo-sphere, hydrosphere, biosphere, and geosphere and all of their
components can be studied sepa-rately. However, the parts are not isolated. Each is related in many
ways to the others, producing a complex and continuously interacting whole that we call the Earth
system.
Earth System Science
A simple example of the interactions among dif-ferent parts of the Earth system occurs every winter as
moisture evaporates from the Pacific Ocean and subsequently falls as rain in the hills of southern
California, triggering destructive de- bris flows (Figure 1–14). The processes that move water from the
hydrosphere to the atmosphere and then to the geosphere have a profound impact on the physical
environment and on the plants and animals (including humans) that inhabit the affected regions.
Scientists have recognized that in order to more fully understand our planet, they must learn how its
individual components (land, water, air, and life-forms) are interconnected. This endeavor, called Earth
system science, aims to
study Earth as a system composed of numerous interacting parts, or subsystems. Using an
interdisciplinary approach, those who practice Earth system science attempt to achieve the level of
understanding necessary to comprehend and solve many of our global environmental problems.
A system is a group of interacting, or interdependent, parts that form a complex whole. Most of us hear
and use the term system frequently. We may service our car’s cooling system, make use of the city’s
transportation system,
(b) Figure 1–13 (a) The ocean contains a significant portion
of Earth’s biosphere. Modern coral reefs are unique and complex examples and are home to about 25
percent of all marine species. Because of this diversity, they are sometimes referred to as the ocean
equivalent of tropical rain forests. (Photo by Darryl Leniuk/agefotostock) (b) Tropical rain forests are
characterized by hundreds of different species per square kilometer. Climate has a strong influence on
the nature of the biosphere. Life, in turn, influences the atmosphere. (Photo by
agefotostock/SuperStock)
16 The Atmosphere: An Introduction to Meteorology
Figure 1–14 This image provides an example of interactions among different parts of the Earth system.
On January 10, 2005, extraordinary rains triggered this debris flow (popularly called a mudslide) in the
coastal community of La Conchita, California. (AP Wideworld Photo)
and be a participant in the political system. A news report might inform us of an approaching weather
system. Further, we know that Earth is just a small part of a largersystem known as the solar system,
which in turn is a subsystem of an even larger system called the Milky Way Galaxy.
The Earth System
The Earth system has a nearly endless array of subsystems in which matter is recycled over and over
again. One example that is described in Box 1–2 traces the movements of carbon among Earth’s four
spheres. It shows us, for example, that
the carbon dioxide in the air and the carbon in living things and in certain rocks is all part of a subsystem
described by the carbon cycle.
The parts of the Earth system are linked so that a change in one part can produce changes in any or all of
the other parts. For example, when a volcano erupts, lava from Earth’s interior may flow out at the
surface and block a nearby valley. This new obstruction influences the region’s drainage system by
creating a lake or causing streams to change course. The large quantities of volcanic ash and gases that
can be emitted during an eruption might be blown high into the atmosphere and influence the amount
of solar energy that can reach Earth’s surface. The result could be a drop in air temperatures over the
entire hemisphere.
Where the surface is covered by lava flows or a thick layer of volcanic ash, existing soils are buried. This
causes the soil-forming processes to begin anew to transform the new surface material into soil ( Figure
1–15). The soil that eventually forms will reflect the interactions among many parts of the Earth
system—the volcanic parent material, the climate, and the impact of biological activity. Of course, there
would also be significant changes in the biosphere. Some organisms and their habitats would be
eliminated by the lava and ash, whereas new settings for life, such as the lake, would be created. The
potential climate change could also impact sensitive life-forms.
The Earth system is characterized by processes that vary on spatial scales from fractions of mil limeters
to thousands of kilometers. Time scales for Earth’s processes range from milliseconds to billions of years. As we learn about Earth, it becomes increasingly clear that despite significant separa-tions in distance
or time, many processes are connected, and a change in one component can influence the entire system.
The Earth system is powered by energy from two sourc- es. The Sun drives external processes that occur
in the atmo-sphere, hydrosphere, and at Earth’s surface. Weather and climate, ocean circulation, and
erosional processes are driv- en by energy from the Sun. Earth’s interior is the second source of energy.
Heat remaining from when our planet formed and heat that is continuously generated by radioac-tive
decay power the internal processes that produce volca- noes, earthquakes, and mountains.
Humans are part of the Earth system, a system in which the living and nonliving components are
entwined and interconnected. Therefore, our actions produce changes in all the other parts. When we
burn gasoline and coal, dispose of our wastes, and clear the land, we cause other parts of the system to
respond, often in unforeseen ways. Throughout this book you will learn about some of Earth’s
subsystems, including the hydrologic system and the climate system. Remember that these components
and we humans are all part of the complex interacting whole we call the Earth system.
Concept Check 1.5
1 What is a system? List three examples.
2 What are the two sources of energy for the Earth system?
Figure 1–15 When Mount St. Helens erupted in May 1980, the area shown here was buried by a volcanic
mudflow. Now, plants are reestablished and new soil is forming. (Photo by Terry Donnelly/ Alamy)
Composition of the Atmosphere
Introduction to the Atmosphere ATMOSPHERE ▸Composition of the Atmosphere
In the days of Aristotle, air was thought to be one of four fundamental substances that could not be
further divided into constituent components. The other three substances were fire, earth (soil), and
water. Even today the term air is sometimes used as if it were a specific gas, which of course it is not.
The envelope of air that surrounds our planet is a mixture of many discrete gases, each with its own
physical properties, in which varying quantities of tiny solid and liq- uid particles are suspended.
Major Components
The composition of air is not constant; it varies from time to time and from place to place (see Box 1–3).
If the water vapor, dust, and other variable components were removed
from the atmosphere, we would find that its makeup is very stable up to an altitude of about 80
kilometers (50 miles).
As you can see in Figure 1–16, two gases—nitrogen and oxygen—make up 99 percent of the volume of
clean, dry air. Although these gases are the most plentiful components of the atmosphere and are of
great significance to life on Earth, they are of little or no importance in affecting weather phenomena. The remaining 1 percent of dry air is mostly the inert gas argon (0.93 percent) plus tiny quantities of a
number of other gases.
Carbon Dioxide
Carbon dioxide, although present in only minute amounts (0.0391 percent, or 391 parts per million), is
nevertheless a meteorologically important constituent of air. Carbon dioxide is of great interest to
meteorologists because it is an efficient absorber of energy emitted by Earth and thus influences the
heating of the atmosphere. Although the proportion of carbon dioxide in the atmosphere is relatively
Chapter 1 Introduction to the Atmosphere 17
18 The Atmosphere: An Introduction to Meteorology
Box 1–2 The Carbon Cycle: One of Earth’s Subsystems
To illustrate the movement of material and energy in the Earth system, let us take a brief look at the
carbon cycle (Figure 1–C). Pure carbon is relatively rare in nature. It
is found predominantly in two minerals: diamond and graphite. Most carbon is bonded chemically to
other elements to
form compounds such as carbon dioxide, calcium carbonate, and the hydrocarbons found in coal and
petroleum. Carbon is also the basic building block of life as it readily combines with hydrogen and
oxygen to form the fundamental organic compounds that compose living things.
In the atmosphere, carbon is found mainly as carbon dioxide (CO2). Atmospheric carbon dioxide is
significant because it is a greenhouse gas, which means it is an efficient absorber of energy emitted by
Earth and thus influences the heating of the atmosphere. Because
many of the processes that operate on
Earth involve carbon dioxide, this gas
is constantly moving into and out of the atmosphere. For example, through the process of
photosynthesis, plants absorb carbon dioxide from the atmosphere to produce the essential organic
compounds needed for growth. Animals that consume these plants (or consume other animals that eat
plants) use these organic compounds as a source of energy and, through the process
FIGURE 1–C Simplified diagram of the carbon cycle, with emphasis on the flow of carbon between the
atmosphere and the hydrosphere, geosphere, and biosphere. The colored arrows show whether the
flow of carbon is into or out of the atmosphere.
Burning and decay of biomass
Photosynthesis by vegetation
Burial of biomass
Photosynthesis and respiration of marine organisms Deposition of carbonate sediments
CO2 dissolves in seawater
Weathering of carbonate rock
Volcanic activity
Weathering of granite
Respiration by land organisms
Burning of fossil fuels
Lithosphere
Sediment and sedimentary rock
CO2 entering the atmosphere
CO2 leaving the atmosphere
Carbon dioxide (0.0391% or 391 ppm)
Nitrogen (78.084%)
1.5 Krypton (Kr) 1.14
of respiration, return carbon dioxide to the atmosphere. (Plants also return some CO2 to the
atmosphere via respiration.) Further,
when plants die and decay or are burned, this biomass is oxidized, and carbon dioxide is returned to the
atmosphere.
Methane (CH4)
Concentration in parts per million (ppm)
uniform, its percentage has been rising steadily for more than a century. Figure 1–17 is a graph showing
the growth in atmospheric CO2 since 1958. Much of this rise is attributed to the burning of everincreasing
quantities of fossil fuels, such as coal and oil. Some of this additional carbon dioxide is
absorbed by the waters of the ocean or is used by plants, but more than 40 percent remains in the air.
Estimates pro- ject that by sometime in the second half of the twenty- first century, carbon dioxide
levels will be twice as high as pre-industrial levels.
Most atmospheric scientists agree that increased carbon dioxide concentrations have contributed to a
warming of Earth’s atmosphere over the past several decades and will continue to do so in the decades
to come. The magnitude of such temperature changes is uncertain and depends partly on the quantities of CO2 contributed by human activities in the years ahead. The role of carbon dioxide in the atmosphere
and its possible effects on climate are examined in more detail in Chapters 2 and 14.
Argon (0.934%)
All others
Oxygen (20.946%)
18.2
Neon (Ne)
Helium (He) 5.24
Hydrogen (H ) 0.5 2
Figure 1–16 Proportional volume of gases composing dry air. Nitrogen and oxygen obviously dominate.
Chapter 1 Introduction to the Atmosphere 19
Not all dead plant material decays immediately back to carbon dioxide. A small percentage is deposited
as sediment. Over long spans of geologic time, considerable biomass is buried with sediment. Under the
right conditions, some of these carbon-rich deposits are converted to fossil fuels—coal, petroleum, or
natural gas. Eventually some
of the fuels are recovered (mined or pumped from a well) and burned to run factories and fuel our
transportation system. One result of fossil-fuel combustion is the release of huge quantities of CO2 into
the atmosphere. Certainly one of the most active parts of the carbon cycle is the movement of CO2 from
the atmosphere to the biosphere and back again.
Carbon also moves from the geosphere and hydrosphere to the atmosphere and back again. For
example, volcanic activity early in Earth’s history is thought to be
the source of much of the carbon dioxide found in the atmosphere. One way that carbon dioxide makes
its way back to the hydrosphere and then to the solid Earth
is by first combining with water to form carbonic acid (H2CO3), which then attacks the rocks that
compose the geosphere. One product of this chemical weathering
of solid rock is the soluble bicarbonate
ion (2HCO3–), which is carried by groundwater and streams to the ocean. Here water-dwelling
organisms extract this dissolved material to produce hard parts (shells) of calcium carbonate (CaCO3).
When the organisms die, these skeletal
remains settle to the ocean floor as biochemical sediment and become sedimentary rock. In fact, the
geosphere is by far Earth’s largest depository of carbon, where it is a constituent of a variety of rocks,
the most abundant being limestone (Figure 1–D). Eventually the limestone
may be exposed at Earth’s surface, where chemical weathering will cause the carbon stored in the rock
to be released to the atmosphere as CO2. 390 380 370 360 350 340 330 320
In summary, carbon moves among all four of Earth’s major spheres. It is essential to every living thing in
the biosphere. In the atmosphere carbon dioxide is an important greenhouse gas. In the hydrosphere,
carbon dioxide is dissolved in lakes, rivers, and the ocean. In the geosphere, carbon is contained in
carbonate-rich sediments and sedimentary rocks and is stored as organic matter dispersed through
sedimentary rocks and as deposits of coal and petroleum.
FIGURE 1–D
A great deal of carbon is
locked up in Earth’s geosphere.
England’s White Chalk Cliffs are an example.
Chalk is a soft, porous type of limestone (CaCO3) consisting mainly of the hard parts of microscopic
organisms called coccoliths (inset). (Photo by Prisma/SuperStock; inset by Steve Gschmeissner/Photo
Researchers, Inc.)
Variable Components
Air includes many gases and particles that vary significantly from time to time and place to place.
Important examples include water vapor, aerosols, and ozone. Although usually present in small
percentages, they can have significant ef- fects on weather and climate.
Water Vapor The amount of water vapor in the air var- ies considerably, from practically none at all up
to about 4 percent by volume. Why is such a small fraction of the
Figure 1–17 Changes in the atmosphere’s carbon dioxide (CO2) as measured at Hawaii’s Mauna Loa
Observatory. The oscillations reflect the seasonal variations in plant growth and decay in the Northern
Hemisphere. During the first 10 years of this record (1958–1967), the average yearly CO2 increase was
0.81 ppm. During the last 10 years (2001–2010) the average yearly increase was 2.04 ppm. (Data from
NOAA)
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
CO2 concentration (ppm)
20 The Atmosphere: An Introduction to Meteorology
Box 1–3 Origin and Evolution of Earth’s Atmosphere
The air we breathe is a stable mixture of 78 percent nitrogen, 21 percent oxygen, nearly 1 percent argon,
and small amounts of gases such as carbon dioxide and water vapor. However, our planet’s original
atmosphere 4.6 billion years ago was substantially different. Earth’s Primitive Atmosphere
Early in Earth’s formation, its atmosphere likely consisted of gases most common in the early solar
system: hydrogen, helium, methane, ammonia, carbon dioxide, and water vapor. The lightest of these
gases, hydrogen and helium, escaped into space because Earth’s gravity was too weak to hold them.
Most of the remaining gases were probably scattered into space by strong solar winds (vast streams of
particles) from a young active Sun. (All stars, including the Sun, apparently experience a highly active
stage early in their evolution, during which solar winds are very intense.)
Earth’s first enduring atmosphere was generated by a process called outgassing, through which gases
trapped in the planet’s interior are released. Outgassing from hundreds of active volcanoes still remains
an important planetary function worldwide (Figure 1–E). However, early in Earth’s history, when
massive heating and fluid-like motion occurred in the planet’s interior, the
gas output must have been immense. Based on our understanding of modern volcanic eruptions, Earth’s
primitive atmosphere probably consisted of mostly water vapor,
carbon dioxide, and sulfur dioxide, with minor amounts of other gases and minimal nitrogen. Most
importantly, free oxygen was not present.
atmosphere so significant? The fact that water vapor is the source of all clouds and precipitation would
be enough to ex- plain its importance. However, water vapor has other roles. Like carbon dioxide, it has
the ability to absorb heat given off by Earth, as well as some solar energy. It is therefore impor-tant
when we examine the heating of the atmosphere.
When water changes from one state to another, such as from a gas to a liquid or a liquid to a solid (see
Figure 4–3,
Students Sometimes Ask…
Could you explain a little more about why the graph in
Figure 1–17 has so many ups and downs?
Sure. Carbon dioxide is removed from the air by photosynthesis, the process by which green plants
convert sunlight into chemical energy. In spring and summer, vigorous plant growth in the extensive
land areas of the Northern Hemisphere removes carbon dioxide from the atmosphere, so the graph
takes a dip. As winter approaches, many plants die or shed leaves. The decay of organic matter returns
carbon dioxide to the air, causing the graph to spike upward.
p. 99), it absorbs or releases heat. This energy is termed latent heat, which means hidden heat. As you
will see in later chapters, water vapor in the atmosphere transports this latent heat from one region to
another, and it is the energy source that drives many storms.
Aerosols The movements of the atmosphere are sufficient to keep a large quantity of solid and liquid
particles sus- pended within it. Although visible dust sometimes clouds the sky, these relatively large particles are too heavy to stay in the air very long. Still, many particles are microscopic and remain
suspended for considerable periods of time. They may originate from many sources, both natural and
human made, and include sea salts from breaking waves, fine soil blown into the air, smoke and soot
from fires, pollen and mi- croorganisms lifted by the wind, ash and dust from volcanic eruptions, and
more (Figure 1–18a). Collectively, these tiny solid and liquid particles are called aerosols.
Aerosols are most numerous in the lower atmosphere near their primary source, Earth’s surface.
Nevertheless, the upper atmosphere is not free of them, because some dust is
FIGURE 1–E Earth’s first enduring atmosphere was formed by a process called outgassing, which
continues today, from hundreds of active volcanoes worldwide. (Photo by Greg Vaughn/Alamy)
Oxygen in the Atmosphere
As Earth cooled, water vapor condensed
to form clouds, and torrential rains began
to fill low-lying areas, which became the oceans. In those oceans, nearly 3.5 billion years ago,
photosynthesizing bacteria began to release oxygen into the water. During photosynthesis, organisms
use the Sun’s energy to produce organic material (energetic molecules of sugar containing hydrogen and
carbon) from carbon dioxide (CO2) and water (H2O). The first bacteria probably used hydrogen sulfide
(H2S) as the source of hydrogen rather than water. One of the earliest bacteria, cyanobacteria (once
called blue-green algae), began to produce oxygen as a by-product of photosynthesis.
Initially, the newly released oxygen was readily consumed by chemical reactions with other atoms and
molecules (particularly iron) in the ocean (Figure 1–F). Once the available iron satisfied its need for
oxygen and as the number of oxygen-generating organisms increased, oxygen began to build in the
atmosphere. Chemical analyses of rocks suggest that a significant amount
of oxygen appeared in the atmosphere as early as 2.2 billion years ago and increased steadily until it
reached stable levels about 1.5 billion years ago. Obviously, the availability of free oxygen had a major
impact on the development of life and vice versa. Earth’s atmosphere evolved together with its lifeforms
from an oxygen-free envelope to an oxygen-rich environment.
FIGURE 1–F These ancient layered, iron-rich rocks, called banded iron formations, were deposited during
a geologic span known as the Precambrian. Much of the oxygen generated as a by-product of
photosynthesis was readily consumed by chemical reactions with iron to produce these rocks. (Photo by
John Cancalosi/Photolibrary)
Chapter 1 Introduction to the Atmosphere 21
carried to great heights by rising currents of air, and other particles are contributed by meteoroids that
disintegrate as they pass through the atmosphere.
From a meteorological standpoint, these tiny, often invisible particles can be significant. First, many act
as sur- faces on which water vapor may condense, an important function in the formation of clouds and fog. Second, aero-sols can absorb or reflect incoming solar radiation. Thus, when an air-pollution
episode is occurring or when ash fills the sky following a volcanic eruption, the amount of sun- light
reaching Earth’s surface can be measurably reduced. Finally, aerosols contribute to an optical
phenomenon we have all observed—the varied hues of red and orange at sunrise and sunset (Figure 1–
18b).
Ozone Another important component of the atmosphere is ozone. It is a form of oxygen that combines
three oxygen atoms into each molecule (O3). Ozone is not the same as the oxygen we breathe, which
has two atoms per molecule (O2). There is very little ozone in the atmosphere. Overall, it rep-resents
just 3 out of every 10 million molecules. Moreover,
its distribution is not uniform. In the lowest portion of the atmosphere, ozone represents less than 1
part in 100 million. It is concentrated well above the surface in a layer called the stratosphere, between
10 and 50 kilometers (6 and 31 miles).
In this altitude range, oxygen molecules (O2) are split into single atoms of oxygen (O) when they absorb
ultraviolet radiation emitted by the Sun. Ozone is then created when a single atom of oxygen (O) and a
molecule of oxygen (O2) collide. This must happen in the presence of a third, neu-tral molecule that
acts as a catalyst by allowing the reaction to take place without itself being consumed in the process.
Ozone is concentrated in the 10- to 50-kilometer height range because a crucial balance exists there:
The ultraviolet radia-tion from the Sun is sufficient to produce single atoms of oxygen, and there are
enough gas molecules to bring about the required collisions.
The presence of the ozone layer in our atmosphere is crucial to those of us who are land dwellers. The
reason is that ozone absorbs the potentially harmful ultraviolet (UV) radiation from the Sun. If ozone did
not filter a great deal of the ultraviolet radiation, and if the Sun’s UV rays reached
Another significant benefit of the “oxygen explosion” is that oxygen molecules (O2) readily absorb
ultraviolet radiation and rearrange themselves to form ozone (O3). Today, ozone is concentrated above
the surface in a layer called the stratosphere, where it absorbs much of the ultraviolet radiation that
strikes the upper atmosphere.
For the first time, Earth’s surface was protected from this type of solar radiation, which is particularly
harmful to DNA. Marine organisms had always been shielded from ultraviolet radiation by
the oceans, but the development of the atmosphere’s protective ozone layer made the continents
more hospitable.
22
The Atmosphere: An Introduction to Meteorology
(a)
(b)
Dust storm Air pollution
(a) This satellite image from November 11, 2002, shows two examples of aerosols. First, a large dust
storm is blowing across northeastern China toward the Korean Peninsula. Second, a dense haze toward
the south (bottom center) is human-generated air pollution. (b) Dust in the air can cause sunsets to be
especially colorful. (Satellite image courtesy of NASA; photo by elwynn/ Shutterstock)
Figure 1–18
the surface of Earth undiminished, land areas on our planet would be uninhabitable for most life as we
know it. Thus, anything that reduces the amount of ozone in the atmo-sphere could affect the wellbeing
of life on Earth. Just such a problem is described in the next section.
Concept Check 1.6
 1 Is air a specific gas? Explain.
 2 What are the two major components of clean, dry air? What proportion does each represent?
 3 Why are water vapor and aerosols important constituents of Earth’s atmosphere?
 4 What is ozone? Why is ozone important to life on Earth?
Ozone Depletion—
A Global Issue
The loss of ozone high in the atmosphere as a consequence of human activities is a serious global-scale
environmental problem. For nearly a billion years Earth’s ozone layer has
protected life on the planet. However, over the past half cen-tury, people have unintentionally placed
the ozone layer in jeopardy by polluting the atmosphere. The most significant of the offending chemicals
are known as chlorofluorocarbons (CFCs). They are versatile compounds that are chemically stable,
odorless, nontoxic, noncorrosive, and inexpensive to produce. Over several decades many uses were
developed for CFCs, including as coolants for air-conditioning and refrigeration equipment, as cleaning
solvents for electronic components, as propellants for aerosol sprays, and in the production of certain
plastic foams.
Students Sometimes Ask…
Isn’t ozone some sort of pollutant?
Yes, you’re right. Although the naturally occurring ozone in the stratosphere is critical to life on Earth, it
is regarded as a pollutant when produced at ground level because it can damage vegetation and be
harmful to human health. Ozone is a major component
in a noxious mixture of gases and particles called photochemical smog. It forms as a result of reactions
triggered by sunlight that occur among pollutants emitted by motor vehicles and industries. Chapter 13
provides more information about this. No one worried about how CFCs might affect the atmo-sphere until three scientists, Paul Crutzen, F.
Sherwood Rowland, and Mario Molina, studied the relationship. In 1974 they alerted the world when
they reported that CFCs were probably reducing the average concentration of ozone in the stratosphere.
In 1995 these scientists were awarded the Nobel Prize in chemistry for their pioneering work.
They discovered that because CFCs are practically inert (that is, not chemically active) in the lower
atmosphere, a portion of these gases gradually makes its way to the ozone layer, where sunlight
separates the chemicals into their constituent atoms. The chlorine atoms released this way, through a
complicated series of reactions, have the net effect of removing some of the ozone.
The Antarctic Ozone Hole
Although ozone depletion by CFCs occurs worldwide, mea-surements have shown that ozone
concentrations take an especially sharp drop over Antarctica during the Southern Hemisphere spring
(September and October). Later, during November and December, the ozone concentration recovers to
more normal levels (Figure 1–19). Between 1980, when it was discovered, and the early 2000s, this wellpublicized
ozone hole intensified and grew larger until it covered an area roughly the size of North
America (Figure 1–20).
The hole is caused in part by the relatively abundant ice particles in the south polar stratosphere. The ice
boosts the effectiveness of CFCs in destroying ozone, thus caus- ing a greater decline than would
otherwise occur. The zone
of maximum depletion is confined to the Antarctic region by a swirling upper-level wind pattern. When
this vortex weakens during the late spring, the ozone-depleted air is no longer restricted and mixes
freely with air from other lati-tudes where ozone levels are higher.
A few years after the Antarctic ozone hole was discov- ered, scientists detected a similar but smaller
ozone thin- ning in the vicinity of the North Pole during spring and early summer. When this pool breaks
up, parcels of ozone- depleted air move southward over North America, Europe, and Asia.
Effects of Ozone Depletion
Because ozone filters out most of the damaging UV radia-tion in sunlight, a decrease in its
concentration permits more of these harmful wavelengths to reach Earth’s surface. What are the effects
of the increased ultraviolet radiation? Each 1 percent decrease in the concentration of stratospheric
ozone increases the amount of UV radiation that reaches Earth’s surface by about 2 percent. Therefore,
because ul-traviolet radiation is known to induce skin cancer, ozone depletion seriously affects human
health, especially among fair-skinned people and those who spend considerable time in the sun.
The fact that up to a half million cases of these cancers occur in the United States annually means that
ozone deple-tion could ultimately lead to many thousands more cases each year.* In addition to raising
the risk of skin cancer, an increase in damaging UV radiation can negatively impact the human immune
system, as well as promote cataracts, a clouding of the eye lens that reduces vision and may cause
blindness if not treated. The effects of additional UV radiation on animal and plant life are also important. There is serious
concern that crop yields and quality will be adversely affected. Some scientists also fear that increased
UV radiation in the Ant- arctic will penetrate the waters surrounding the continent and impair or destroy
the microscopic plants, called phy-toplankton, that represent the base of the food chain. A decrease in
phytoplankton, in turn, could reduce the popu- lation of copepods and krill that sustain fish, whales,
pen- guins, and other marine life in the high latitudes of the Southern Hemisphere.
Montreal Protocol
What has been done to protect the atmosphere’s ozone layer? Realizing that the risks of not curbing
CFC emissions were difficult to ignore, an international agreement known as the Montreal Protocol on
Substances That Deplete the Ozone Layer was concluded under the auspices of the United Nations in
late 1987. The protocol established legally binding controls
* For more on this, see Severe and Hazardous Weather: “The Ultraviolet Index,” p. 49.
Chapter 1 Introduction to the Atmosphere 23
30
25
20
15
10
5
Area of North
America
Extent of 2006
ozone hole
Extent 2010 ozone
h
of ole
Aug Sep
Oct Nov Dec
Figure 1-19 Changes in the size of the Antarctic ozone hole during 2006 and 2010. The ozone hole in
both years began
to form in August and was well developed in September and October. As is typical, each year the ozone hole persisted through November and disappeared in December. At its maximum, the area of the ozone
hole was about 22 million square kilometers in 2010, an area nearly as large as all of North America.
Million square kilometers
24 The Atmosphere: An Introduction to Meteorology
Area of North Americ
Extent
Area of Antarctica
ozone hole
of
1979
Ozone (Dobson Units) 110 220 330 440 550
30 25a 20
15
10
5
1980 1985 1990 1995 2000 2005 2010 2015
2010 Year
The two satellite images show ozone distribution in the Southern Hemisphere on the days in September
1979 and 2010 when the ozone hole was largest. The dark blue shades over Antarctica correspond to
the region with the sparsest ozone. The ozone hole is not technically a “hole” where no ozone is present
but is actually a region of exceptionally depteted ozone in
the stratosphere over the Antarctic that occurs in the spring. The small graph traces changes in the
maximum size of the ozone hole, 1980–2010. (NOAA)
Figure 1–20
on the production and consumption of gases known to cause ozone depletion. As the scientific
understanding of ozone depletion improved after 1987 and substitutes and alternatives became
available for the offending chemicals, the Montreal Protocol was strengthened several times. More than
190 nations eventually ratified the treaty.
The Montreal Protocol represents a positive international response to a global environment problem. As
a result of the action, the total abundance of ozone-depleting gases in the atmosphere has started to decrease in recent years. Accord- ing to the U.S. Environmental Protection Agency (U.S. EPA), the ozone
layer has not grown thinner since 1998 over most of the world.* If the nations of the world continue to
follow the provisions of the protocol, the decreases are expected to continue throughout the twenty –
first century. Some offend- ing chemicals are still increasing but will begin to decrease in coming
decades. Between 2060 and 2075, the abundance of ozone-depleting gases is projected to fall to values
that exist- ed before the Antarctic ozone hole began to form in the 1980s.
Concept Check 1.7
 1 What are CFCs, and what is their connection to the ozone
 problem?
 2 During what time of year is the Antarctic ozone hole well developed?
 3 Describe three effects of ozone depletion.
 4 What is the Montreal Protocol?
* U.S. EPA, Achievements in Stratospheric Ozone Protection, Progress Report. EPA-430-R-07-001, April
2007, p. 5.
Vertical Structure of the Atmosphere
ATMOSPHERE
Introduction to the Atmosphere
▸Extent of the Atmosphere/Thermal Structure of the Atmosphere
To say that the atmosphere begins at Earth’s surface and ex-tends upward is obvious. However, where
does the atmo-sphere end and where does outer space begin? There is no sharp boundary; the
atmosphere rapidly thins as you travel away from Earth, until there are too few gas molecules to detect.
Pressure Changes
To understand the vertical extent of the atmosphere, let us examine the changes in atmospheric
pressure with height. Atmospheric pressure is simply the weight of the air above. At sea level the
average pressure is slightly more than 1000 millibars. This corresponds to a weight of slightly more than
1 kilogram per square centimeter (14.7 pounds per square inch). Obviously, the pressure at higher
altitudes is less (Figure 1–21).
One-half of the atmosphere lies below an altitude of 5.6 kilometers (3.5 miles). At about 16 kilometers
(10 miles), 90 percent of the atmosphere has been traversed, and above 100 kilometers (62 miles) only
0.00003 percent of all the gases composing the atmosphere remain.
At an altitude of 100 kilometers the atmosphere is so thin that the density of air is less than could be
found in the most perfect artificial vacuum at the surface. Nevertheless, the atmosphere continues to
even greater heights. The truly Million square kilometers
Chapter 1 Introduction to the Atmosphere 25
Kathy Orr, Broadcast Meteorologist
KATHY ORR is an award-winning broadcast meteorologist in Philadelphia. (Photo courtesy of Kathy Orr)
not the ‘rip and read’ of years gone by. We take data from the supercomputers in Wash- ington or
models by the Navy and make our own forecasts. There are some services that provide forecasts locally
and nationally, but they’re not located where we are. I can look out the window and tell whether those
fore- casts are going to be accurate or not.”
As a weathercaster, Orr has worked to promote education in science and math. For three years, she led
a community program called Kidcasters. By offering children a chance to present the weather on TV, Orr
hoped to interest elementary school children in science and math. For the past nine sum- mers, she has
conducted a similar program called Orr at the Shore. Each program highlights environmental issues
along the New Jersey coast.
My job is to explain complicated ideas to people in an uncomplicated way.
Orr continues to promote science literacy by volunteering for the American Meteoro- logical Society’s
DataStreme Atmosphere Project. As a DataStreme mentor, she has vis- ited dozens of schools to train
teachers in the science of meteorology. The teachers then promote the use of weather lessons in their
districts to pique student interest in science, mathematics, and technology. Orr considers her forecasts
educational as well. “My job is to explain complicated ideas to people in an uncomplicated way.”
Being a weathercaster, Orr says, is demanding but also exhilarating. “In TV,
the hours are crazy. If you work mornings, you’re up at 2 AM; if nights, you’re up until midnight. So you
really have to love it. But if you do, you’ll find a way. And I feel blessed to have done this for so long.”
Kathy Orr is a trusted and familiar face
on the airwaves of Philadelphia. As chief meteorologist for CBS3, Orr has kept the City of Brotherly Love
abreast of the weather for 18 years and earned 10 regional Emmy awards in the process.
Orr calls being a television weathercaster a dream come true.
Orr calls being a television weather- caster a dream come true. Growing up in Syracuse, New York, Orr
operated her own miniature weather station and marveled at the snow squalls that howled across Lake
Ontario. “It could be a sunny afternoon, then the wind would blow over the lake. All of
a sudden there was a blinding blizzard,” she says.
When not watching the skies, Orr stayed glued to her family’s TV set. At the time, she couldn’t see how to combine her two major interests. “There weren’t any women doing the weather on
television back then. There were also not a lot of meteorologists on TV; it was less about the science and
more for comic relief,” she says.
She majored in broadcasting at Syracuse University and went on to earn a second degree in
meteorology at the State University of New York at Oswego. There she learned the basis for the snow
squalls that transfixed her as a girl. “These kinds of phenomena are associated with being on the
downwind side of a Great Lake. When wind comes along, the lake acts like a snowmaking machine.”
While still in school, Orr landed a job as
the weathercaster on a Syracuse station’s brand-new morning show. She’s remained a television
meteorologist ever since.
Today, Orr says, being a trained meteorol- ogist “is definitely a competitive advantage. It’s
rarefied nature of the outer atmosphere is described very well by Richard Craig:
The earth’s outermost atmosphere, the part above a few hundred kilometers, is a region of extremely
low density. Near sea level, the number of atoms and molecules in a cubic centimeter of air is about 2 3
1019; near 600 km, it is only about 2 3 107, which is the sea-level value divided by a million million. At
sea level, an atom or molecule can be expected, on the average, to move about 7 3 1026 cm before
colliding with another particle; at the 600-km level, this distance, called the “mean free path,” is about
10 km. Near
sea level, an atom or molecule, on the average, undergoes about 7 3 109 such collisions each second;
near 600 km, this number is reduced to about 1 each minute.*
The graphic portrayal of pressure data (Figure 1–21) shows that the rate of pressure decrease is not
constant. Rather, pressure decreases at a decreasing rate with an increase in altitude until, beyond an
altitude of about 35 kilometers (22 miles), the decrease is negligible.
*Richard Craig, The Edge of Space: Exploring the Upper Atmosphere (New York: Doubleday & Company,
Inc., 1968), p. 130.
26
The Atmosphere: An Introduction to Meteorology
36 32 28 24 20 16 12
8 4
lies below
22 20 18 16 14 12 10 8 6 4 2
Cap t. Kittinger, USAF
1961 31. (102,800
Air press
Air pressure at top of Mt. Evere
(29,035 ft) is
314 m
b
3 km ft)
ure = 9.6
st
atm this
50% of
osphere altitude
mb
200
400
Pressure (mb)
1000
This jet is cruising at an altitude of 10 kilometers (6.2 miles). (Photo by inter- light/Shutterstock)
Question 1 Refer to the graph in Figure 1–21. What is the approximate air pressure where the jet is
flying?
Question 2 About what percentage of the atmosphere is below the jet (assuming that the pressure at
the surface is 1000 millibars)?
Although measurements had not been taken above a height of about 10 kilometers (6 miles), scientists
believed that the temperature continued to decline with height to a value of absolute zero (–273°C) at
the outer edge of the atmo-sphere. In 1902, however, the French scientist Leon Philippe Teisserenc de
Bort refuted the notion that temperature Figure 1–22 Temperatures drop with an increase in altitude in the troposphere. Therefore, it is possible
to have snow on a mountaintop and warmer, snow-free lowlands below. (Photo by David Wall/Alamy)
600 800
Figure 1–21 Atmospheric pressure changes with altitude.
The rate of pressure decrease with an increase in altitude is not constant. Rather, pressure decreases
rapidly near Earth’s surface and more gradually at greater heights.
Put another way, data illustrate that air is highly compressible—that is, it expands with decreasing
pressure and becomes compressed with increasing pressure. Conse- quently, traces of our atmosphere
extend for thousands of kilometers beyond Earth’s surface. Thus, to say where the atmosphere ends
and outer space begins is arbitrary and, to a large extent, depends on what phenomenon one is study –
ing. It is apparent that there is no sharp boundary.
In summary, data on vertical pressure changes show that the vast bulk of the gases making up the
atmosphere is very near Earth’s surface and that the gases gradually merge with the emptiness of space.
When compared with the size of the solid Earth, the envelope of air surrounding our planet is indeed
very shallow.
Temperature Changes
By the early twentieth century much had been learned about the lower atmosphere. The upper
atmosphere was partly known from indirect methods. Data from balloons and kites had revealed that
the air temperature dropped with increas- ing height above Earth’s surface. This phenomenon is felt by
anyone who has climbed a high mountain and is obvious in pictures of snow-capped mountaintops rising
above snow- free lowlands (Figure 1–22).
Altitude (km)
Altitude (miles)
decreases continuously with an increase in altitude. In studying the results of more than 200 balloon
launchings, Teisserenc de Bort found that the temperature stopped decreas- ing and leveled off at an
altitude between 8 and 12 kilometers (5 and 7.5 miles). This sur- prising discovery was at first doubted,
but subsequent data-gathering confirmed his findings. Later, through the use of balloons and rocketsounding
techniques, the temper- ature structure of the atmosphere up to great heights became clear.
Today the atmosphere is divided vertically into four layers on the basis of temperature (Figure 1–23).
Troposphere The bottom layer in which we live, where temperature decreases with an increase in
altitude, is the troposphere. The term was coined in 1908 by Teisserrenc de Bort and literally means the
region where air “turns over,” a reference to the apprecia- ble vertical mixing of air in this lowermost
zone.
140 130 120 110 100 90 80 70 60 50 40 30 20 10
Aurora
Meteor
THERMOSPHERE
Mesopause
MESOSPHERE
Stratopause
STRATOSPHERE
Tropopause
TROPOSPHERE
10 20 30 30
90
80
70
60
50
40
30
20
10
50 ̊C
Chapter 1 Introduction to the Atmosphere
27
Maximum ozone
The temperature decrease in the troposphere
is called the environmental lapse
rate. Its average value is 6.5°C per kilome-ter (3.5°F per 1000 feet), a figure known as
the normal lapse rate. It should be emphasized,
however, that the environmental
lapse rate is not a constant but rather can be
highly variable and must be regularly measured.
To determine the actual environmental
lapse rate as well as gather information
about vertical changes in air pressure, wind,
and humidity, radiosondes are used. A radiosonde is an instrument package that is attached to a
balloon and trans- mits data by radio as it ascends through the atmosphere (Figure 1–24). The
environmental lapse rate can vary dur- ing the course of a day with fluctuations of the weather, as well
as seasonally and from place to place. Sometimes shallow layers where temperatures actually increase
with height are observed in the troposphere. When such a rever-sal occurs, a temperature inversion is
said to exist.*
The temperature decrease continues to an average height of about 12 kilometers (7.5 miles). Yet the
thick- ness of the troposphere is not the same everywhere. It reaches heights in excess of 16 kilometers
(10 miles) in the tropics, but in polar regions it is more subdued, extend- ing to 9 kilometers (5.5 miles)
or less (Figure 1–25). Warm surface temperatures and highly developed thermal mix- ing are responsible
for the greater vertical extent of the tro- posphere near the equator. As a result, the environmental
lapse rate extends to great heights; and despite relatively high surface temperatures below, the lowest
tropospheric temperatures are found aloft in the tropics and not at the poles.
*Temperature inversions are described in greater detail in Chapter 13.
Mt. Everest
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
–140 –120 –100 –80 –60 –40 –20 0 20 40 60 80 100 120 ̊F 32
Temperature
Figure 1–23 Thermal structure of the atmosphere.
The troposphere is the chief focus of meteorologists because it is in this layer that essentially all
important weather phenomena occur. Almost all clouds and certainly all precipitation, as well as all our
violent storms, are born in this lowermost layer of the atmosphere. This is why the troposphere is often
called the “weather sphere.”
Stratosphere Beyond the troposphere lies the stratosphere; the boundary between the troposphere
and the stratosphere is known as the tropopause. Below the tropopause, atmospheric properties are
readily transferred by large-scale turbulence and mixing, but above it, in the stratosphere, they are not. In the stratosphere, the tempera-ture at first remains nearly constant to a height of about 20 kilometers
(12 miles) before it begins a sharp increase that continues until the stratopause is encountered at a
height of about 50 kilometers (30 miles) above Earth’s surface. Higher temperatures occur in the
stratosphere because it is in this layer that the atmosphere’s ozone is concentrated. Recall that ozone
absorbs ultraviolet radiation from the Sun. Con-sequently, the stratosphere is heated by the Sun.
Although the maximum ozone concentration exists between 15 and 30 kilometers (9 and 19 miles), the
smaller amounts of ozone above this height range absorb enough UV energy to cause the higher
observed temperatures.
Height (km)
Height (miles)
Temperature
28 The Atmosphere: An Introduction to Meteorology
Pole
Tropopause
Tropical tropopause
Middle latitude
tropopause
Polar tropopause
Equator
30 27 24 21 18 15 12
9 6 3 0
–70 –60 –50 –40 –30 –20 –10 Temperature ( ̊C)
0 10 20
Figure 1–24 A lightweight instrument package, the radiosonde, is suspended below a 2-meter-wide
weather balloon. As
the radiosonde is carried aloft, sensors measure pressure, temperature, and relative humidity. A radio
transmitter sends the measurements to a ground receiver. By tracking the radiosonde
in flight, information on wind speed and direction aloft is also obtained. Observations where winds aloft
are obtained are called “rawinsonde” observations. Worldwide, there are about 900 upper-air
observation stations. Through international agreements, data are exchanged among countries. (Photo
by Mark Burnett/ Photo Researchers, Inc.) Mesosphere In the third layer, the mesosphere, temper- atures again decrease with height until at the
mesopause, some 80 kilometers (50 miles) above the surface, the aver- age temperature approaches
290°C (2130°F). The coldest temperatures anywhere in the atmosphere occur at the me-sopause. The
pressure at the base of the mesosphere is only about one-thousandth that at sea level. At the
mesopause, the atmospheric pressure drops to just one-millionth that at sea level. Because accessibility
is difficult, the mesosphere is one of the least explored regions of the atmosphere. The reason is that it
cannot be reached by the highest-flying airplanes and research balloons, nor is it accessible to the
Figure 1–25 Differences in the height of the tropopause. The variation in the height of the tropopause,
as shown on the small inset diagram, is greatly exaggerated.
lowest-orbiting satellites. Recent technical developments are just beginning to fill this knowledge gap.
Thermosphere The fourth layer extends outward from the mesopause and has no well-defined upper
limit. It is the thermosphere, a layer that contains only a tiny frac- tion of the atmosphere’s mass. In the
extremely rarified air of this outermost layer, temperatures again increase, due to the absorption of very
shortwave, high-energy solar radia-tion by atoms of oxygen and nitrogen.
Temperatures rise to extremely high values of more than 1000°C (1800°F) in the thermosphere. But such
temperatures are not comparable to those experienced near Earth’s sur- face. Temperature is defined in
terms of the average speed at which molecules move. Because the gases of the thermo-sphere are
moving at very high speeds, the temperature is very high. But the gases are so sparse that collectively
they possess only an insignificant quantity of heat. For this reason, the temperature of a satellite
orbiting Earth in the thermosphere is determined chiefly by the amount of solar
Altitude (km)
Chapter 1 Introduction to the Atmosphere 29
radiation it absorbs and not by the high temperature of the almost nonexistent surrounding air. If an
astronaut inside were to expose his or her hand, the air in this layer would not feel hot.
Concept Check 1.8
 1 Does air pressure increase or decrease with an increase in
 altitude? Is the rate of change constant or variable? Explain.
 2 Is the outer edge of the atmosphere clearly defined? Explain.
 3 The atmosphere is divided vertically into four layers on the basis of temperature. List these
layers in order from lowest to highest. In which layer does practically all of our weather occur?
 4 Why does temperature increase in the stratosphere?
 5 Why are temperatures in the thermosphere not strictly
 comparable to those experienced near Earth’s surface? Vertical Variations in Composition
In addition to the layers defined by vertical variations in temperature, other layers, or zones, are also
recognized in the atmosphere. Based on composition, the atmosphere is often divided into two layers:
the homosphere and the heterosphere. From Earth’s surface to an altitude of about 80 kilometers (50
miles), the makeup of the air is uniform in terms of the proportions of its component gases. That is, the
composition is the same as that shown earlier, in Figure 1–16. This lower uniform layer is termed the
homosphere, the zone of homogeneous composition.
In contrast, the very thin atmosphere above 80 kilometers is not uniform. Because it has a
heterogeneous composition, the term heterosphere is used. Here the gases are arranged into four
roughly spherical shells, each with a distinctive composition. The lowermost layer is dominated by
molec- ular nitrogen (N2), next, a layer of atomic oxygen (O) is encountered, followed by a layer
dominated by helium (He) atoms, and finally a region consisting largely of hydrogen (H) atoms. The
stratified nature of the gases making up the heterosphere varies according to their weights. Molecular
nitrogen is the heaviest, and so it is lowest. The lightest gas, hydrogen, is outermost.
Ionosphere
Located in the altitude range between 80 to 400 kilometers (50 to 250 miles), and thus coinciding with
the lower portions of the thermosphere and heterosphere, is an electrically charged layer known as the
ionosphere. Here molecules of nitrogen and atoms of oxygen are readily ionized as they
When this weather balloon was launched, the surface temperature was 17°C. It is now at an altitude of 1
kilometer. (Photo by David R. Frazier/ Photo Researchers, Inc.)
Question 1 What term is applied to the instrument package being car-ried aloft by the balloon?
Question 2 In what layer of the atmosphere is the balloon? Question 3 If average conditions prevail,
what air temperature is the
instrument package recording? How did you figure this out?
Question 4 How will the size of the balloon change, if at all, as it rises through the atmosphere? Explain.
absorb high-energy shortwave solar energy. In this process, each affected molecule or atom loses one or
more electrons and becomes a positively charged ion, and the electrons are set free to travel as electric
currents.
Although ionization occurs at heights as great as 1000 kilometers (620 miles) and extends as low as
perhaps 50 kilometers (30 miles), positively charged ions and nega-tive electrons are most dense in the
range of 80 to 400 kilo- meters (50 to 250 miles). The concentration of ions is not great below this zone
because much of the short-wavelength radiation needed for ionization has already been depleted.
30 The Atmosphere: An Introduction to Meteorology In addition, the atmospheric density at this level results in a large percentage of free electrons being
swiftly cap-tured by positively charged ions. Beyond the 400-kilometer (250-mile) upward limit of the
ionosphere, the concentra-tion of ions is low because of the extremely low density of the air. Because
so few molecules and atoms are present, relatively few ions and free electrons can be produced.
The electrical structure of the ionosphere is not uni- form. It consists of three layers of varying ion
density. From bottom to top, these layers are called the D, E, and F lay- ers, respectively. Because the
production of ions requires direct solar radiation, the concentration of charged parti- cles changes from
day to night, particularly in the D and E zones. That is, these layers weaken and disappear at night and
reappear during the day. The uppermost layer, or F layer, on the other hand, is present both day and
night. The density of the atmosphere in this layer is very low, and positive ions and electrons do not
meet and recombine as rapidly as they do at lesser heights, where density is higher. Consequently, the
concentration of ions and electrons in the F layer does not change rapidly, and the layer, although weak,
remains through the night.
The Auroras
As best we can tell, the ionosphere has little impact on our daily weather. But this layer of the
atmosphere is the site of one of nature’s most interesting spectacles, the auroras (Figure 1–26). The
aurora borealis (northern lights) and
its Southern Hemisphere counterpart, the aurora australis (southern lights), appear in a wide variety of
forms. Some-times the displays consist of vertical streamers in which there can be considerable
movement. At other times the auroras appear as a series of luminous expanding arcs or as a quiet glow
that has an almost foglike quality.
The occurrence of auroral displays is closely correlated in time with solar-flare activity and, in geographic
location, with Earth’s magnetic poles. Solar flares are massive mag- netic storms on the Sun that emit
enormous amounts of energy and great quantities of fast-moving atomic particles. As the clouds of
protons and electrons from the solar storm approach Earth, they are captured by its magnetic field,
which in turn guides them toward the magnetic poles. Then, as the ions impinge on the ionosphere,
they energize the atoms of oxygen and molecules of nitrogen and cause them to emit light—the glow of
the auroras. Because the occur-rence of solar flares is closely correlated with sunspot activ- ity, auroral
displays increase conspicuously at times when sunspots are most numerous.
Concept Check 1.9
1 Distinguish between the homosphere and the heterosphere. 2 What is the ionosphere? Where in the
atmosphere is it located? 3 What is the primary cause of the auroras?
Figure 1–26 Aurora borealis (northern lights) as seen from Alaska. The same phenomenon occurs
toward the South Pole, where it is called the aurora australis (southern lights). (Photo by agefotostock/
SuperStock)
Give It Some Thought 1. Determine which statements refer to weather and which refer to climate. (Note: One
statement includes aspects of both weather and climate.)
2. a. The baseball game was rained out today.
a. January is Omaha’s coldest month.
b. North Africa is a desert.
c. The high this afternoon was 25°C.
d. Last evening a tornado ripped through central Oklahoma.
e. I am moving to southern Arizona because it is warm and sunny.
f. Thursday’s low of –20°C is the coldest temperature ever recorded for that city.
g. It is partly cloudy.
3. After entering a dark room, you turn on a wall switch,
4. but the light does not come on. Suggest at least three hypotheses that might explain this
observation.
5. Making accurate measurements and observations is
a basic part of scientific inquiry. The accompanying radar image, showing the distribution and
intensity
of precipitation associated with a storm, provides
one example. Identify three additional images in this chapter that illustrate ways in which
scientific data are gathered. Suggest advantages that might be associated with each example.
greenhouse gases have increased global average
temperatures.
b. One or two studies suggest that hurricance intensity is increasing.
5. Refer to Figure 1–21 to answer the following questions.
6. If you were to climb to the top of Mount Everest,
7. how many breaths of air would you have to take at
8. that altitude to equal one breath at sea level?
9. If you are flying in a commercial jet at an altitude of 12 kilometers, about what
percentage of the atmosphere’s mass is below you?
6. If you were ascending from the surface of Earth to the top of the atmosphere, which one of the
following would be most useful for determining the layer of the atmosphere you were in? Explain.
a. Doppler radar
b. Hygrometer (humidity)
c. Weather satellited. Barometer (air pressure)
e. Thermometer (temperature)
7. The accompanying photo provides an example of interactions among different parts of the Earth
system. It is a view of a mudflow that was triggered by extraordinary rains. Which of Earth’s four
“spheres” were involved in this natural disaster that buried a small town on the Philippine island of
Leyte? Describe how each contributed to the mudflow.
(Photo by AP Photo/Pat Roque)
8. Where would you expect the thickness of the troposphere (that is, the distance between Earth’s
surface and the tropopause) to be greater: over Hawaii or Alaska? Why? Do you think it is likely that the
thickness of the troposphere over Alaska is different in January than in July? If so, why?
Chapter 1 Introduction to the Atmosphere 31
(Image by National Weather Service)
4. During a conversation with your meteorology professor, she makes the two statements listed below.
Which can be considered a hypothesis? Which is more likely a theory?
a. After several decades, the science community has determined that human-generated
32 The Atmosphere: An Introduction to Meteorology
INTRODUCTION TO THE ATMOSPHERE IN REVIEW
 ● Meteorology is the scientific study of the atmosphere. Weather refers to the state of the
atmosphere at a given time and place. It is constantly changing, sometimes from hour to hour
and other times from day to day. Climate is an aggregate
 of weather conditions, the sum of all statistical weather information that helps describe a place
or region. The
nature of both weather and climate is expressed in terms
of the same basic elements, those quantities or properties measured regularly. The most
important elements are (1) air temperature, (2) humidity, (3) type and amount of cloudiness, (4)
type and amount of precipitation, (5) air pressure, and
 (6) the speed and direction of the wind.
 ● All science is based on the assumption that the natural world
 behaves in a consistent and predictable manner. The process by which scientists gather facts
through observation and careful measurement and formulate scientific hypotheses and theories
is often referred to as the scientific method.  ● Earth’s four spheres include the atmosphere (gaseous envelope), the geosphere (solid Earth),
the hydrosphere (water portion),
and the biosphere (life). Each sphere is composed of many interrelated parts and is intertwined
with all the other spheres.
 ● Although each of Earth’s four spheres can be studied separately, they are all related in a
complex and continuously interacting whole that we call the Earth system. Earth system science
uses an interdisciplinary approach to integrate the knowledge of several academic fields in the
study of our planet and its global environmental problems.
 ● A system is a group of interacting parts that form a complex whole. The two sources of energy
that power the Earth system are (1) the Sun, which drives the external processes that occur in
the atmosphere, hydrosphere, and at Earth’s surface, and (2) heat from Earth’s interior that
powers the internal processes that produce volcanoes, earthquakes, and mountains.
 ● Air is a mixture of many discrete gases, and its composition varies from time to time and
place to place. After water vapor, dust, and other variable components are removed, two gases,
nitrogen and oxygen, make up 99 percent of the volume of the remaining clean, dry air. Carbon
dioxide, although present
 in only minute amounts (0.0391 percent, or 391 ppm), is an efficient absorber of energy emitted
by Earth and thus influences the heating of the atmosphere.
 ● The variable components of air include water vapor, dust particles, and ozone. Like carbon
dioxide, water vapor can absorb heat given off by Earth as well as some solar energy. When
water vapor changes from one state to another, it absorbs or releases heat. In the atmosphere,
water vapor transports this latent (“hidden”) heat from one place
 to another, and it is the energy source that helps drive
many storms. Aerosols (tiny solid and liquid particles) are meteorologically important because
these often-invisible particles act as surfaces on which water can condense and are also
absorbers and reflectors of incoming solar radiation. Ozone, a form of oxygen that combines
three oxygen atoms into each molecule (O3), is a gas concentrated in the 10- to 50-kilometer
height range in the atmosphere that absorbs the potentially harmful ultraviolet (UV) radiation
from the Sun.
● Over the past half century, people have placed Earth’s
ozone layer in jeopardy by polluting the atmosphere with chlorofluorocarbons (CFCs), which remove
some of the gas. Ozone concentrations take an especially sharp drop over Antarctica duri ng the
Southern Hemisphere spring (September and October). Ozone depletion seriously affects human health,
especially among fair-skinned people and those who spend considerable time in the Sun. The Montreal
Protocol, concluded under the auspices of the United Nations, represents a positive international
response to the ozone problem. ● No sharp boundary to the upper atmosphere exists. The atmosphere simply thins as you travel away
from Earth, until there are too few gas molecules to detect. Traces of atmosphere extend for thousands
of kilometers beyond Earth’s surface.
● Using temperature as the basis, the atmosphere is divided into four layers. The temperature decrease
in the troposphere, the bottom layer in which we live, is called the environmental lapse rate. Its average
value is 6.5°C per kilometer, a figure known
as the normal lapse rate. The environmental lapse rate is not a constant and must be regularly
measured using radiosondes. The thickness of the troposphere is generally greater in the tropics than in
polar regions. Essentially all important weather phenomena occur in the troposphere. Beyond the
troposphere lies the stratosphere; the boundary between the troposphere and stratosphere is known as
the tropopause. In the stratosphere, the temperature at first remains constant to a height of about 20
kilometers (12 miles) before it begins a sharp increase due to the absorption of ultraviolet radiation
from the Sun by ozone. The temperatures continue to increase until the stratopause is encountered at a
height of about 50 kilometers (30 miles). In the mesosphere, the third layer, temperatures again
decrease with height until the mesopause, some 80 kilometers (50 miles) above the surface. The fourth
layer, the thermosphere, with no well-defined upper limit, consists of extremely rarefied air.
Temperatures here increase with an increase in altitude.
● The atmosphere is often divided into two layers, based
on composition. The homosphere (zone of homogeneous composition), from Earth’s surface to an
altitude of about
80 kilometers (50 miles), consists of air that is uniform in terms of the proportions of its component
gases. Above 80 kilometers, the heterosphere (zone of heterogenous composition) consists of gases
arranged into four roughly spherical shells, each with a distinctive composition. The stratified nature of
the gases in the heterosphere varies according to their weights.
● Occurring in the altitude range between 80 and 400 kilometers (50 and 250 miles) is an electri cally
charged layer known as the ionosphere. Here molecules of nitrogen and atoms of oxygen are readily
ionized as they absorb high-energy, shortwave solar energy. Three layers of varying ion density make up
the ionosphere. Auroras (the aurora borealis, northern lights, and its Southern Hemisphere counterpart
the aurora australis, southern lights) occur within the ionosphere. Auroras form as clouds of protons
and electrons ejected from the Sun during solar-flare activity enter the atmosphere near Earth’s
magnetic poles and energize the atoms of oxygen and molecules of nitrogen, causing them to emit
light—the glow of the auroras.
aerosols (p. 21)
air (p. 17)
atmosphere (p. 13) aurora australis (p. 29) aurora borealis (p. 29) biosphere (p. 15) climate (p. 5)
elements of weather and climate (p. 7) environmental lapse rate (p. 26) geosphere (p. 13)
hydrosphere (p. 14)
hypothesis (p. 9)
ionosphere (p. 29) mesopause (p. 27) mesosphere (p. 27) meteorology (p. 4) ozone (p. 21)
PROBLEMS
radiosonde (p. 26) stratopause (p. 27) stratosphere (p. 27) system (p. 16) theory (p. 10) thermosphere (p.
27) tropopause (p. 27) troposphere (p. 26) weather (p. 5)
VOCABULARY REVIEW
8. a.
On a spring day a middle-latitude city (about 40°N latitude) has a surface (sea-level) temperature of 10°C.
If vertical soundings reveal a nearly constant environmental lapse rate of 6.5°C per kilometer and a
temperature
at the tropopause of –55°C, what is the height of the tropopause?
Chapter 1 Introduction to the Atmosphere 33
10. Refer to the newspaper-type weather map in Figure 1–3 to answer the following:
a. Estimate the predicted high temperatures in central New York State and the
northwest corner of Arizona.
b. Where is the coldest area on the weather map? Where is the warmest?
c. On this weather map, H stands for the center of a region of high pressure. Does it
appear as though high pressure is associated with precipitation or fair weather?
d. Which is warmer—central Texas or central Maine? Would you normally expect this to
be the case?
11. Refer to the graph in Figure 1–5 to answer the following questions about temperatures in New
York City:
a. What is the approximate average daily high temperature in January? In July?
b. Approximately what are the highest and lowest temperatures ever recorded?
12. Refer to the graph in Figure 1–7. Which year had the greatest number of billion-dollar weather
disasters? How many events occurred that year? In which year was the damage amount
greatest?
13. Refer to the graph in Figure 1–21 to answer the following:
a. Approximately how much does the air pressure drop (in
b. millibars) between the surface and 4 kilometers? (Use a
c. surface pressure of 1000 millibars.)
d. How much does the pressure drop between 4 and 8 e. kilometers?
f. Based on your answers to parts a and b, answer the
g. following: With an increase in altitude, air pressure decreases at a(n) (constant,
increasing, decreasing) rate. Underline the correct answer.
5. If the temperature at sea level were 23°C, what would the air temperature be at a height of 2
kilometers, under average conditions?
6. Use the graph of the atmosphere’s thermal structure (Figure 1–23) to answer the following:
14. What are the approximate height and temperature of the stratopause?
15. At what altitude is the temperature lowest? What is the temperature at that height?
7. Answer the following questions by examining the graph in Figure 1–25:
16. In which one of the three regions (tropics, middle latitudes, poles) is the surface temperature
lowest?
17. In which region is the tropopause encountered at the lowest altitude? The highest? What are
the altitudes and temperatures of the tropopause in those regions?
b. On the same spring day a station near the equator
has a surface temperature of 25°C, 15°C higher than
the middle-latitude city mentioned in part a. Vertical soundings reveal an environmental lapse rate of
6.5°C per kilometer and indicate that the tropopause is encountered at 16 kilometers. What is the air
temperature at the tropopause?
Log in to www.mymeteorologylab.com for animations, videos, MapMaster interactive maps, GEODe
media, In the News RSS feeds, web links, glossary flashcards, self-study quizzes and a Pearson eText
version of this book to enhance your study of Introduction to the Atmosphere.
Hundreds of cars stranded on Chicago’s Lake Shore Drive on February 2, 2011, following
a winter blizzard of historic proportions. (AP Photo/ Kiichiro Sato)
After completing this chapter, you should be able to:
 Distinguish between weather and climate and name the basic elements of weather and climate.
 List several important atmospheric hazards and identify those that are storm related.
 Construct a hypothesis and distinguish between a scientific hypothesis and a scientific
theory.
 List and describe Earth’s four major spheres.
 Define system and explain why Earth can be thought of as a system.
List the major gases composing Earth’s atmosphere and identify those components that are most
important meteorologically.
Explain why ozone depletion is a significant global issue.
Interpret a graph that shows changes in air pressure from Earth’s surface to the top of the atmosphere.
Sketch and label a graph showing the thermal structure of the atmosphere.
Distinguish between homosphere and heterosphere.
3
4 The Atmosphere: An Introduction to Meteorology Focus on the Atmosphere
everywhere on our planet. The United States likely has the greatest variety of weather of any country in
the world. Severe weather events, such as tornadoes, flash floods, and intense thunderstorms, as well as
hurricanes and bliz-zards, are collectively more frequent and more damaging in the United States than
in any other nation. Beyond its direct impact on the lives of individuals, the weather has a strong effect
on the world economy, by influencing agri- culture, energy use, water resources, transportation, and
industry.
Weather clearly influences our lives a great deal. Yet it is also important to realize that people influence
the atmo-sphere and its behavior as well (Figure 1–2). There are, and will continue to be, significant
political and scientific deci-sions to make involving these impacts. Answers to ques-tions regarding air
pollution and its control and the effects of various emissions on global climate are important exam- ples.
So there is a need for increased awareness and under-standing of our atmosphere and its behavior.
Meteorology, Weather, and Climate
The subtitle of this book includes the word meteorology. Meteorology is the scientific study of the
atmosphere and the phenomena that we usually refer to as weather. Along with geology, oceanography,
and astronomy, meteorology is considered one of the Earth sciences—the sciences that seek to
understand our planet. It is important to point out that there are not strict boundaries among the Earth sciences; in many situations, these sciences overlap. Moreover, all of the Earth sciences involve an
understanding and applica-tion of knowledge and principles from physics, chemistry, and biology. You
will see many examples of this fact in your study of meteorology.
Acted on by the combined effects of Earth’s motions and energy from the Sun, our planet’s formless and
invis- ible envelope of air reacts by producing an infinite variety of weather, which in turn creates the
basic pattern of global climates. Although not identical, weather and climate have much in common.
Weather is constantly changing, sometimes from hour to hour and at other times from day to day. It is a
term that refers to the state of the atmosphere at a given time and place. Whereas changes in the
weather are continuous and sometimes seemingly erratic, it is nevertheless possible to arrive at a
generalization of these variations. Such a descrip-tion of aggregate weather conditions is termed
climate. It is based on observations that have been accumulated over many decades. Climate is often
defined simply as “average weather,” but this is an inadequate definition. In order to accurately portray
the character of an area, variations and extremes must also be included, as well as the probabili-ties
that such departures will take place. For example, it is necessary for farmers to know the average rainfall
during the growing season, and it is also important to know the frequency of extremely wet and
extremely dry years. Thus, climate is the sum of all statistical weather information that helps describe a
place or region.
ATMOSPHERE
Introduction to the Atmosphere ▸Weather and Climate
Weather influences our everyday activities, our jobs, and our health and comfort. Many of us pay little
attention to the weather unless we are inconvenienced by it or when it adds to our enjoyment of
outdoor activities. Nevertheless, there are few other aspects of our physical environment that affect our
lives more than the phenomena we collectively call the weather.
Weather in the United States
The United States occupies an area that stretches from the tropics to the Arctic Circle. It has thousands
of miles of coast- line and extensive regions that are far from the influence of the ocean. Some
landscapes are mountainous, and others are dominated by plains. It is a place where Pacific storms
strike the West Coast, while the East is sometimes influenced by events in the Atlantic and the Gulf of
Mexico. For those in the center of the country, it is common to experience weather events triggered
when frigid southward-bound Canadian air masses clash with northward-moving tropical ones from the
Gulf of Mexico.
Stories about weather are a routine part of the daily news. Articles and items about the effects of heat,
cold, floods, drought, fog, snow, ice, and strong winds are com-monplace (Figure 1–1). Memorable
weather events occur Figure1–1 Fewaspectsofourphysicalenvironmentinfluence our daily lives more than the weather.
Tornadoes are intense and destructive local storms of short duration that cause an average of about 55
deaths each year. (Photo by Wave RF/Photolibrary)
Chapter 1 Introduction to the Atmosphere 5
(a) (b)
Figure 1–2 These examples remind us that people influence the atmosphere and its behavior.
(a) Motor vehicles are a significant contributor to air pollution. This traffic jam was in Kuala Lumpur,
Malaysia. (Photo by Ron Yue/Alamy) (b) Smoke bellows from a coal-fired electricity-generating plant in
New Delhi, India, in June 2008. (AP Photo/Gurindes Osan)
Maps similar to the one in Figure 1–3 are familiar to everyone who checks the weather report in the
morning newspaper or on a television station. In addition to showing predicted high temperatures for
the day, this map shows other basic weather information about cloud cover, precipi-tation, and fronts.
Suppose you were planning a vacation trip to an unfa- miliar place. You would probably want to know
what kind of weather to expect. Such information would help as you selected clothes to pack and could
influence decisions regarding activities you might engage in during your stay. Unfortunately, weather
forecasts that go beyond a few days are not very dependable. Thus, it would not be possible to get a
reliable weather report about the conditions you are likely to encounter during your vacation.
Instead, you might ask someone who is familiar with the area about what kind of weather to expect.
“Are
thunderstorms common?” “Does it get cold at night?” “Are the afternoons sunny?” What you are
seeking is information about the climate, the conditions that are typical for that
Students Sometimes Ask …
Does meteorology have anything to do with meteors?
Yes, there is a connection. Most people use the word meteor when referring to solid particles
(meteoroids) that enter Earth’s atmosphere from space and “burn up” due to friction (“shooting stars”).
The term meteorology was coined in 340 BC, when the Greek philosopher Aristotle wrote a book titled
Meteorlogica, which included explanations of atmospheric and astronomical phenomena. In Aristotle’s
day anything that fell from or was seen in the sky was called a meteor. Today we distinguish between
particles of ice or water in the atmosphere (called hydrometeors) and extraterrestrial objects called
meteoroids, or meteors.
6
The Atmosphere: An Introduction to Meteorology
30s 20s H
10s 40s
50s
–0s
50s
cannot predict the weather. Although the place may usually (climatically) be warm, sunny, and dry
during the time of your planned vacation, you may actually experience cool, over- cast, and rainy
weather. There is a well-known saying that summarizes this idea: “Climate is what you expect, but
weather is what you get.”
The nature of both weather and cli-mate is expressed in terms of the same basic elements—those
quantities or properties that are measured regu- larly. The most important are (1) the temperature of
the air, (2) the humid- ity of the air, (3) the type and amount of cloudiness, (4) the type and amount of
precipitation, (5) the pressure exert- ed by the air, and (6) the speed and direction of the wind. These
elements constitute the variables by which weather patterns and climate types are depicted. Although
you will study these elements separately at first, keep in mind that they are very much inter-
0s
L
0s 20s
H
20s 0s
10s
50s
60s
–10s
Rain T-storm Snow Ice
place. Another useful source of such information is the great variety of climate tables, maps, and graphs
that are available. For example, the map in Figure 1–4 shows the average per- centage of possible
sunshine in the United States for the month of November, and the graph in Figure 1–5 shows average
daily high and low temperatures for each month, as well as extremes, for New York City.
Such information could, no doubt, help as you planned your trip. But it is important to realize that
climate data –0s
30s
40s 10s 70sH
20s
40s
A typical newspaper weather map for a day in late December. The color bands show the high
temperatures forecast for the day.
Figure 1–3
30 40
50 60
70
80 90
30
30 40
30 40
50
60
90
80
70 60
Figure 1–4 Mean percentage of possible sunshine for November. Southern Arizona is clearly the
sunniest area. By contrast, parts of the Pacific Northwest receive a much smaller percentage of the
possible sunshine. Climate maps such as this one are based on many years of data.
30s
50s
80s
Mostly cloudy
40 Mostly sunny
Partly cloudy
60
related. A change in one of the elements often produces changes in the others.
Concept Check 1.1
1 Distinguish among meteorology, weather, and climate.
2 List the basic elements of weather and climate.
48
44
40
36
32 90 28
ger price tag.
Between 1980 and 2010 the United States experienced
99 weather-related disasters in which overall damages
Chapter 1 Introduction to the Atmosphere 7
by all other weather events combined. Moreover, although
severe storms and floods usually generate more attention, 110 droughts can be just as devastating and
carry an even bigRecord
daily
Av
dail
highs
erage
y highs
Average
dai
ly lows Record daily lows
100
24 20
and costs reached or exceeded $1 billion (Figure 1–7). The 80 combined costs of these events exceeded
$725 billion (nor-
70
malized to 2007 dollars)! During the decade 1999–2008, an average of 629 direct weather fatalities
occurred per year in the United States. During this span, the annual economic impacts of adverse
weather on the national highway system alone exceeded $40 billion, and weather-related air traffic
delays caused $4.2 billion in annual losses.
16 60
12 8 4 0
50
40
At appropriate places throughout this book, you will Two entire chapters (Chapter 10 and Chapter 11)
focus
This is a scene on a day in late April in southern Arizona’s Organ Pipe Cactus National Monument. (Photo
by Michael Collier)
Question 1 Write two brief statements about the locale in this image—one that relates to weather and
one that relates to climate.
30 have an opportunity to learn about atmospheric hazards.
–4
–8
–12 10 –16
–20
– 24 –28 –32
20
0 –10 –20
JFMAMJJASOND Month Figure 1–5 Graph showing daily temperature data for New York City. In addition to the average daily
maximum and minimum temperatures for each month, extremes are also shown. As this graph shows,
there can be significant departures from the average.
Atmospheric Hazards: Assault by the Elements
Natural hazards are a part of living on Earth. Every day they adversely affect literally millions of people
worldwide and are responsible for staggering damages. Some, such as earthquakes and volcanic
eruptions, are geological. Many others are related to the atmosphere.
Occurrences of severe weather are far more fascinating than ordinary weather phenomena. A
spectacular light- ning display generated by a severe thunderstorm can elicit both awe and fear ( Figure
1–6a). Of course, hurricanes and tornadoes attract a great deal of much-deserved attention. A single
tornado outbreak or hurricane can cause billions of dollars in property damage, much human suffering,
and many deaths.
Of course, other atmospheric hazards adversely affect us. Some are storm related, such as blizzards, hail,
and freezing rain. Others are not direct results of storms. Heat waves, cold waves, fog, wildfires, and
drought are impor-tant examples (Figure 1–6b). In some years the loss of human life due to excessive
heat or bitter cold exceeds that caused
Temperature ( ̊C)
Temperature ( ̊F)
8 The Atmosphere: An Introduction to Meteorology
(a)
(b)
Figure 1–6 (a) Many people have incorrect perceptions of weather dangers and are unaware of the
relative differences of weather threats to human life. For example, they are awed by
the threat of hurricanes and tornadoes and plan accordingly on how to respond (for example, “Tornado
Awareness Week” each spring) but fail to realize that lightning and winter storms can be greater threats.
(Photo by Mark Newman/Superstock) (b) During the summer, dry weather coupled with lightning and
strong winds contribute to wildfire danger. Millions of acres are burned each year, especially in the West.
The loss of anchoring vegetation sets the stage for accelerated erosion when heavy rains subsequently
occur. Near Boulder, Colorado, October 10, 2010. (AP Photo/ The Daily Camera, Paul Aiken)
The Nature
of Scientific Inquiry
As members of a modern society, we are constantly reminded of the benefits derived from science. But
what exactly is the nature of scientific inquiry? Developing an understanding of how science is done and
how scientists work is an impor-tant theme in this book. You will explore the difficulties of gathering data and some of the ingenious methods that have been developed to overcome these difficulties. You
will also
almost entirely on hazardous weather. In addition, a number of the book’s special-interest boxes are
devoted to a broad variety of severe and hazardous weather, including heat waves, winter storms,
floods, dust storms, drought, mudflows, and lightning.
Every day our planet experiences an incredible assault by the atmosphere, so it is important to develop
an aware- ness and understanding of these significant weather events.
Concept Check 1.2
1 List at least five storm-related atmospheric hazards.
2 What are three atmospheric hazards that are not directly storm related?
916 892
Chapter 1 Introduction to the Atmosphere 9 Hypothesis
Once facts have been gathered and principles have been formulated to describe a natural phenomenon,
investigators try to explain
2
1
1
1
1
9
7
4
2
768howorwhythingshappeninthemanner observed. They often do this by construct-
644ingatentative(oruntested)explanation, which is called a scientific hypothesis. It is
520bestifaninvestigatorcanformulatemore than one hypothesis to explain a given set of
46observations.Ifanindividualscientistisun- able to devise multiple hypotheses, others in the scientific
community will almost always develop alternative explanations. A spirited debate frequently ensues. As
a result, exten-sive research is conducted by proponents of opposing hypotheses, and the results are
made available to the wider scientific com-
32 28 14 00
munity in scientific journals.
Before a hypothesis can become an
accepted part of scientific knowledge, it must pass objective testing and analysis. If a hypothesis cannot
be tested, it is not scientifically useful, no matter how in-teresting it might seem. The verification process requires that predictions be made based on the hypothesis being considered and the predictions
be tested by being compared against objective observations
Year
Between 1980 and 2010 the United States experienced 99 weather-related disasters in which overall
damages and costs reached or exceeded $1 billion. This bar graph shows the number of events that
occurred each year and the damage amounts in billions of dollars (normalized to 2007 dollars). The total
losses for the
99 events exceeded $725 billion! For more about these extraordinary events see
www.ncdc.noaa.gov/oa/reports/billionz.html. (After NOAA)
Figure 1–7
see examples of how hypotheses are formulated and tested, as well as learn about the development of
some significant scientific theories.
All science is based on the assumption that the natu-ral world behaves in a consistent and predictable
manner that is comprehensible through careful, systematic study. The overall goal of science is to
discover the underly- ing patterns in nature and then to use this knowledge to make predictions about
what should or should not be expected, given certain facts or circumstances. For example, by
understanding the processes and condi-tions that produce certain cloud types, meteorologists are often
able to predict the approximate time and place of their formation.
The development of new scientific knowledge involves some basic logical processes that are universally
accepted. To determine what is occurring in the natural world, sci- entists collect scientific facts through
observation and measurement. The types of facts that are collected often seek to answer a well-defined
question about the natural world, such as “Why does fog frequently develop in this place?” or “What
causes rain to form in this cloud type?” Because some error is inevitable, the accuracy of a particu- lar
measurement or observation is always open to question. Nevertheless, these data are essential to
science and serve as a springboard for the development of scientific theories (Box 1–1).
of nature. Put another way, hypotheses must fit observa-tions other than those used to formulate them
in the first place. Hypotheses that fail rigorous testing are ultimately discarded. The history of science is
littered with discarded hypotheses. One of the best known is the Earth-centered model of the
universe—a proposal that was supported by the apparent daily motion of the Sun, Moon, and stars
around Earth.
Theory
When a hypothesis has survived extensive scrutiny and when competing ones have been eliminated, a
hypothesis may be elevated to the status of a scientific theory. In ev- eryday language we may say,
“That’s only a theory.” But a scientific theory is a well-tested and widely accepted view that the scientific
community agrees best explains certain observable facts. Some theories that are extensively documented and extremely well supported are comprehensive in
scope. An example from the Earth sciences is the theory of plate tec-tonics, which provides the
framework for understanding the origin of mountains, earthquakes, and volcanic activity. It also explains
the evolution of continents and ocean basins through time. As you will see in Chapter 14, this theory
also helps us understand some important aspects of climate change through long spans of geologic time.
1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
Number of events
Damage amounts in billions of dollars
10 The Atmosphere: An Introduction to Meteorology
Box 1–1 Monitoring Earth from Space
Scientific facts are gathered in many ways, including through laboratory experiments and field
observations and measurements. Satellites provide another very important source of data. Satellite
images give us perspectives that are difficult to gain from more traditional sources (Figure 1–A).
Moreover, the high-tech instruments aboard many satellites enable scientists to gather information
from remote regions where data are otherwise scarce.
The image in Figure 1–B is from NASA’s Tropical Rainfall Measuring Mission (TRMM). TRMM is a
research satellite designed to expand our understanding of Earth’s water (hydrologic) cycle and its role
in our climate system. By covering the region between
the latitudes 35° north and 35° south, it provides much-needed data on rainfall and the heat release
associated with rainfall. Many types of measurements and images are possible. Instruments aboard the
TRMM satellite have greatly expanded our ability to collect precipitation data. In addition to recording
data for land areas, this satellite provides extremely precise measurements of rainfall over the oceans
where conventional land-based instruments cannot see. This
is especially important because much of Earth’s rain falls in ocean-covered tropical areas, and a great
deal of the globe’s weather-producing energy comes from
heat exchanges involved in the rainfall process. Until the TRMM, information on
the intensity and amount of rainfall over the tropics was scanty. Such data are crucial to understanding
and predicting global climate change.
FIGURE 1–B This map of rainfall for December 7–13, 2004, in Malaysia was constructed using TRMM
data. Over 800 millimeters (32 inches) of rain fell along the east coast of the peninsula (darkest red area).
The extraordinary rains caused extensive flooding and triggered many mudflows. (NASA/TRMM image)
Scientific Methods The processes just described, in which scientists gather facts through observations and formulate
scientific hypotheses and theories, is called the scientific method. Contrary to popu- lar belief, the
scientific method is not a standard recipe that scientists apply in a routine manner to unravel the secrets
of our natural world. Rather, it is an endeavor that involves creativity and insight. Rutherford and
Ahlgren put it this
FIGURE 1–A Satellite image of a massive winter storm on February 1, 2011. During a winter marked by
several crippling storms, this one stands out. Heavy snow, ice, freezing rain, and frigid winds battered
nearly two-thirds of the contiguous United States. In this image, the storm measures about 2000
kilometers (1240 miles) across. Satellites allow us to monitor the development and movement of major
weather systems. (NASA)
Sumatra
7.9 200
Malaysia
15.7 23.6 31.5 Inches 400 600 800 mm
way: “Inventing hypotheses or theories to imagine how the world works and then figuring out how they
can be put to the test of reality is as creative as writing poetry, composing music, or designing
skyscrapers.”*
*F. James Rutherford and Andrew Ahlgren, Science for All Americans (New York: Oxford University Press,
1990), p. 7.
Singapore
There is not a fixed path that scientists always follow that leads unerringly to scientific knowledge.
Nevertheless, many scientific investigations involve the following steps: (1) A question is raised about
the natural world; (2) scientific data are collected that relate to the question (Figure 1–8); (3) questions
are posed that relate to the data, and one or more working hypotheses are developed that may answer
these questions; (4) observations and experiments are devel- oped to test the hypotheses; (5) the
hypotheses are accepted, modified, or rejected, based on extensive testing; (6) data and results are
shared with the scientific community for critical and further testing.
Other scientific discoveries may result from purely theoretical ideas that stand up to extensive
examination. Some researchers use high-speed computers to simulate what is happening in the “real”
world. These models are useful when dealing with natural processes that occur on very long time scales
or take place in extreme or inacces-sible locations. Still other scientific advancements have been made
when a totally unexpected happening occurred during an experiment. These serendipitous discoveries
are more than pure luck; as Louis Pasteur stated, “In the field of observation, chance favors only the
prepared mind.” Scientific knowledge is acquired through several ave- nues, so it might be best to describe the nature of
scientific
Chapter 1 Introduction to the Atmosphere 11 Students Sometimes Ask…
In class you compared a hypothesis to a theory. How is each one different from a scientific law?
A scientific law is a basic principle that describes a particular behavior of nature that is generally narrow
in scope and can be stated briefly—often as a simple mathematical equation. Because scientific laws
have been shown time and time again to be consistent with observations and measurements, they are
rarely discarded. Laws may, however, require modifications to fit new findings. For example, Newton’s
laws of motion are still useful
for everyday applications (NASA uses them to calculate satellite trajectories), but they do not work at
velocities approaching the speed of light. For these circumstances, they have been supplanted by
Einstein’s theory of relativity.
inquiry as the methods of science rather than the scientific method. In addition, it should always be
remembered that even the most compelling scientific theories are still simpli- fied explanations of the
natural world.
Concept Check 1.3
1 How is a scientific hypothesis different from a scientific
theory?
2 List the basic steps followed in many scientific investigations.
Figure 1–8 Gathering data and making careful observations
are a basic part of scientific inquiry. (a) This Automated Surface Observing System (ASOS) installation is
one of nearly 900 in use for data gathering as part of the U.S. primary surface observing network. (Photo
by Bobbé Christopherson) (b) These scientists are working with a sediment core recovered from the
ocean floor. Such cores often contain useful data about Earth’s climate history. (Photo by Science
Source/Photo Researchers, Inc.)
(a)
(b)
12 The Atmosphere: An Introduction to Meteorology Students Sometimes Ask…
Who provides all the data needed to prepare
a weather forecast?
Data from every part of the globe are needed to produce accurate weather forecasts. The World
Meteorological Organization (WMO) was established by the United Nations to coordinate scientific
activity related to weather and climate. It consists of 187 member states and territories, representing all parts of the globe. Its World Weather Watch provides up-to-the-minute standardized observations
through member-operated observation systems. This global system involves more than 15 satellites,
10,000 land- observation and 7300 ship stations, hundreds of automated data buoys, and thousands of
aircraft.
Earth’s Spheres
The images in Figure 1–9 are considered to be classics be- cause they let humanity see Earth differently
than ever be- fore. Figure 1–9a, known as “Earthrise,” was taken when the Apollo 8 astronauts orbited
the Moon for the first time in December 1968. As the spacecraft rounded the Moon, Earth appeared to
rise above the lunar surface. Figure 1–9b, referred to as “The Blue Marble,” is perhaps the most widely
reproduced image of Earth; it was taken in December 1972 by the crew of Apollo 17 during the last
manned lunar mis-sion. These early views profoundly altered our conceptual- izations of Earth and
remain powerful images decades after they were first viewed. Seen from space, Earth is breathtak- ing
in its beauty and startling in its solitude. The photos remind us that our home is, after all, a planet—
small, self- contained, and in some ways even fragile. Bill Anders, the
Apollo 8 astronaut who took the “Earthrise” photo, expressed it this way: “We came all this way to
explore the Moon, and the most important thing is that we discovered the Earth.”
As we look closely at our planet from space, it becomes apparent that Earth is much more than rock and
soil. In fact, the most conspicuous features in Figure 1–9a are not continents but swirling clouds
suspended above the sur- face of the vast global ocean. These features emphasize the importance of
water on our planet.
The closer view of Earth from space shown in Figure 1–9b helps us appreciate why the physical
environment is tradi-tionally divided into three major parts: the solid Earth, the water portion of our
planet, and Earth’s gaseous envelope.
It should be emphasized that our environment is highly integrated and is not dominated by rock, water,
or air alone. It is instead characterized by continuous interactions as air comes in contact with rock, rock
with water, and water with air. Moreover, the biosphere, the totality of life forms on our planet, extends
into each of the three physical realms and is an equally integral part of the planet.
The interactions among Earth’s four spheres are incal- culable. Figure 1–10 provides us with one easy-tovisualize
example. The shoreline is an obvious meeting place for rock, water, and air. In this scene, ocean
waves that were created by the drag of air moving across the water are breaking against the rocky shore.
The force of the water can be powerful, and the erosional work that is accomplished can be great.
On a human scale Earth is huge. Its surface area occu- pies 500,000,000 square kilometers (193 million
square miles). We divide this vast planet into four independent parts. Because each part loosely
occupies a shell around Earth, we call them spheres. The four spheres include the geosphere (solid
Earth), the atmosphere (gaseous envelope), the hydrosphere (water portion), and the biosphere (life). Figure 1–9 (a) View, called “Earthrise,” that greeted the Apollo 8 astronauts as their spacecraft emerged
from behind the Moon. (NASA) (b) Africa and Arabia are prominent in this classic image called “The Blue
Marble” taken from Apollo 17. The tan cloud-free zones over the land coincide with major desert
regions. The band of clouds across central Africa is associated with a much wetter climate that in places
sustains tropical rain forests. The dark blue of the oceans and the swirling cloud patterns remind us of
the importance of the oceans and the atmosphere. Antarctica, a continent covered by glacial ice, is
visible at the South Pole. (NASA)
(a) (b)
Figure 1–10 The shoreline is one obvious example of an interface—a common boundary where different
parts of a system interact. In this scene, ocean waves (hydrosphere) that were created by the force of
moving air (atmosphere) break against a rocky shore (geosphere). (Photo by Radius Images/
photolibrary.com)
It is important to remember that these spheres are not separated by well-defined boundaries; rather,
each sphere is intertwined with all of the others. In addition, each of Earth’s four major spheres can be
thought of as being com- posed of numerous interrelated parts.
The Geosphere
Beneath the atmosphere and the ocean is the solid Earth, or geosphere. The geosphere extends from
the surface to the center of the planet, a depth of about 6400 kilometers (nearly 4000 miles), making it
by far the largest of Earth’s four spheres.
Based on compositional differences, the geosphere is divided into three principal regions: the dense
inner sphere, called the core; the less dense mantle; and the crust, which is the light and very thin outer
skin of Earth.
Soil, the thin veneer of material at Earth’s surface that supports the growth of plants, may be thought of
as part of all four spheres. The solid portion is a mixture of weathered rock debris (geosphere) and
organic matter from decayed plant and animal life (biosphere). The decomposed and dis- integrated
rock debris is the product of weathering process-es that require air (atmosphere) and water
(hydrosphere). Air and water also occupy the open spaces between the solid particles.
The Atmosphere
Earth is surrounded by a life-giving gaseous envelope called the atmosphere (Figure 1–11). When we
watch a high-flying jet plane cross the sky, it seems that the atmosphere extends upward for a great
distance. However, when compared to the thickness (radius) of the solid Earth (about 6400 kilome -ters
[4000 miles]), the atmosphere is a very shallow layer. More than 99 percent of the atmosphere is within
30 kilome-ters (20 miles) of Earth’s surface. This thin blanket of air is nevertheless an integral part of
the planet. It not only pro- vides the air that we breathe but also acts to protect us from the dangerous
radiation emitted by the Sun. The energy exchanges that continually occur between the atmosphere and
Earth’s surface and between the atmosphere and space produce the effects we call weather. If, like the Moon, Earth had no atmosphere, our planet would not only be lifeless, but many of the processes and
interactions that make the surface such a dynamic place could not operate.
The Hydrosphere
Earth is sometimes called the blue planet. More than any-thing else, water makes Earth unique. The
hydrosphere is a dynamic mass that is continually on the move, evapo-rating from the oceans to the
atmosphere, precipitating to
Chapter 1 Introduction to the Atmosphere 13
14
The Atmosphere: An Introduction to Meteorology
160 140 120 100
80 60 40 20
Noctilucent clouds
Top of troposphere
Figure 1–11 This unique image of Earth’s atmosphere merging with the emptiness
of space resembles an abstract painting.
It was taken in June 2007 by a Space Shuttle crew member. The silvery streaks (called noctilucent clouds)
high in the blue area are at a height of about 80 kilometers (50 miles). Air pressure at this height is less
than one-thousandth of that at sea level.
The reddish zone in the lower portion of the image is the densest part of the atmosphere. It is here, in a
layer called the troposphere, that practically all weather phenomena occur. Ninety percent of Earth’s
atmosphere occurs within just 16 kilometers (10 miles) of the surface. (NASA)
(2.5 miles) and in boiling hot springs. Moreover, air currents can carry microorganisms many kilometers
into the atmo- sphere. But even when we consider these extremes, life still must be thought of as being
confined to a narrow band very near Earth’s surface.
Plants and animals depend on the physical environ- ment for the basics of life. However, organisms do
more than just respond to their physical environment. Through
Earth’s surface
the land, and running back to the ocean again. The global ocean is certainly the most prominent feature
of the hydro-sphere, blanketing nearly 71 percent of Earth’s surface to an average depth of about 3800
meters (12,500 feet). It accounts for about 97 percent of Earth’s water (Figure 1–12). How- ever, the hydrosphere also includes the fresh water found in clouds, streams, lakes, and glaciers, as we ll as that
found underground.
Although these latter sources consti-tute just a tiny fraction of the total, they are much more important
than their meager percentage indicates. Clouds, of course, play a vital role in many weath- er and
climate processes. In addition to providing the fresh water that is so vital to life on land, streams,
glaciers, and groundwater are responsible for sculpt- ing and creating many of our planet’s varied
landforms.
The Biosphere
The biosphere includes all life on Earth (Figure 1–13). Ocean life is concentrated in the sunlit surface
waters of the sea. Most life on land is also concentrated near the surface, with tree roots and burrowing
animals reaching a few me-ters underground and flying insects and birds reaching a kilometer or so
above the surface. A surprising variety of life forms are also adapted to extreme en- vironments. For
example, on the ocean floor, where pressures are extreme and no light penetrates, there are places
where vents spew hot, mineral-rich fluids that support communities of ex- otic life-forms. On land, some
bacteria thrive in rocks as deep as 4 kilometers
Oceans 97.2%
Hydrosphere
2.8%
Glaciers 2.15%
Freshwater lakes 0.009% Saline lakes and inland seas 0.008%
Soil moisture 0.005% Atmosphere 0.001% Stream channels 0.0001%
Groundwater 0.62%
Stream channel
Glaciers
Groundwater (spring)
Nonocean Component (% of total hydrosphere)
Figure1–12 DistributionofEarth’swater.Obviously,mostofEarth’swaterisintheoceans. Glacial ice
represents about 85 percent of all the water outside the oceans. When only liquid freshwater is
considered, more than 90 percent is groundwater. (Glacier photo by Bernhard Edmaier/Photo
Researchers, Inc.; stream photo by E.J. Tarbuck; and groundwater photo by Michael Collier)
Altitude in kilometers (km)
Chapter 1 Introduction to the Atmosphere 15 (a)
countless interactions, life forms help maintain and alter their physical environment. Without life, the
makeup and nature of the geosphere, hydrosphere, and atmosphere would be very different.
Concept Check 1.4
 1 Compare the height of the atmosphere to the
 thickness of the geosphere.
 2 How much of Earth’s surface do oceans cover?
 3 How much of the planet’s total water supply do the oceans represent?
 4 List and briefly define the four spheres that constitute our environment.
Earth as a System
Anyone who studies Earth soon learns that our planet is a dynamic body with many separate but highly
interactive parts, or spheres. The atmo-sphere, hydrosphere, biosphere, and geosphere and all of their
components can be studied sepa-rately. However, the parts are not isolated. Each is related in many
ways to the others, producing a complex and continuously interacting whole that we call the Earth
system.
Earth System Science
A simple example of the interactions among dif-ferent parts of the Earth system occurs every winter as
moisture evaporates from the Pacific Ocean and subsequently falls as rain in the hills of southern
California, triggering destructive de- bris flows (Figure 1–14). The processes that move water from the
hydrosphere to the atmosphere and then to the geosphere have a profound impact on the physical
environment and on the plants and animals (including humans) that inhabit the affected regions.
Scientists have recognized that in order to more fully understand our planet, they must learn how its
individual components (land, water, air, and life-forms) are interconnected. This endeavor, called Earth
system science, aims to
study Earth as a system composed of numerous interacting parts, or subsystems. Using an
interdisciplinary approach, those who practice Earth system science attempt to achieve the level of
understanding necessary to comprehend and solve many of our global environmental problems.
A system is a group of interacting, or interdependent, parts that form a complex whole. Most of us hear
and use the term system frequently. We may service our car’s cooling system, make use of the city’s
transportation system,
(b) Figure 1–13 (a) The ocean contains a significant portion
of Earth’s biosphere. Modern coral reefs are unique and complex examples and are home to about 25
percent of all marine species. Because of this diversity, they are sometimes referred to as the ocean
equivalent of tropical rain forests. (Photo by Darryl Leniuk/agefotostock) (b) Tropical rain forests are
characterized by hundreds of different species per square kilometer. Climate has a strong influence on
the nature of the biosphere. Life, in turn, influences the atmosphere. (Photo by
agefotostock/SuperStock)
16 The Atmosphere: An Introduction to Meteorology
Figure 1–14 This image provides an example of interactions among different parts of the Earth system.
On January 10, 2005, extraordinary rains triggered this debris flow (popularly called a mudslide) in the
coastal community of La Conchita, California. (AP Wideworld Photo)
and be a participant in the political system. A news report might inform us of an approaching weather
system. Further, we know that Earth is just a small part of a largersystem known as the solar system,
which in turn is a subsystem of an even larger system called the Milky Way Galaxy.
The Earth System
The Earth system has a nearly endless array of subsystems in which matter is recycled over and over
again. One example that is described in Box 1–2 traces the movements of carbon among Earth’s four
spheres. It shows us, for example, that
the carbon dioxide in the air and the carbon in living things and in certain rocks is all part of a subsystem
described by the carbon cycle.
The parts of the Earth system are linked so that a change in one part can produce changes in any or all of
the other parts. For example, when a volcano erupts, lava from Earth’s interior may flow out at the
surface and block a nearby valley. This new obstruction influences the region’s drainage system by
creating a lake or causing streams to change course. The large quantities of volcanic ash and gases that
can be emitted during an eruption might be blown high into the atmosphere and influence the amount
of solar energy that can reach Earth’s surface. The result could be a drop in air temperatures over the
entire hemisphere.
Where the surface is covered by lava flows or a thick layer of volcanic ash, existing soils are buried. This
causes the soil-forming processes to begin anew to transform the new surface material into soil ( Figure
1–15). The soil that eventually forms will reflect the interactions among many parts of the Earth
system—the volcanic parent material, the climate, and the impact of biological activity. Of course, there
would also be significant changes in the biosphere. Some organisms and their habitats would be
eliminated by the lava and ash, whereas new settings for life, such as the lake, would be created. The
potential climate change could also impact sensitive life-forms.
The Earth system is characterized by processes that vary on spatial scales from fractions of mil limeters
to thousands of kilometers. Time scales for Earth’s processes range from milliseconds to billions of years. As we learn about Earth, it becomes increasingly clear that despite significant separa-tions in distance
or time, many processes are connected, and a change in one component can influence the entire system.
The Earth system is powered by energy from two sourc- es. The Sun drives external processes that occur
in the atmo-sphere, hydrosphere, and at Earth’s surface. Weather and climate, ocean circulation, and
erosional processes are driv- en by energy from the Sun. Earth’s interior is the second source of energy.
Heat remaining from when our planet formed and heat that is continuously generated by radioac-tive
decay power the internal processes that produce volca- noes, earthquakes, and mountains.
Humans are part of the Earth system, a system in which the living and nonliving components are
entwined and interconnected. Therefore, our actions produce changes in all the other parts. When we
burn gasoline and coal, dispose of our wastes, and clear the land, we cause other parts of the system to
respond, often in unforeseen ways. Throughout this book you will learn about some of Earth’s
subsystems, including the hydrologic system and the climate system. Remember that these components
and we humans are all part of the complex interacting whole we call the Earth system.
Concept Check 1.5
1 What is a system? List three examples.
2 What are the two sources of energy for the Earth system?
Figure 1–15 When Mount St. Helens erupted in May 1980, the area shown here was buried by a volcanic
mudflow. Now, plants are reestablished and new soil is forming. (Photo by Terry Donnelly/ Alamy)
Composition of the Atmosphere
Introduction to the Atmosphere ATMOSPHERE ▸Composition of the Atmosphere
In the days of Aristotle, air was thought to be one of four fundamental substances that could not be
further divided into constituent components. The other three substances were fire, earth (soil), and
water. Even today the term air is sometimes used as if it were a specific gas, which of course it is not.
The envelope of air that surrounds our planet is a mixture of many discrete gases, each with its own
physical properties, in which varying quantities of tiny solid and liq- uid particles are suspended.
Major Components
The composition of air is not constant; it varies from time to time and from place to place (see Box 1–3).
If the water vapor, dust, and other variable components were removed
from the atmosphere, we would find that its makeup is very stable up to an altitude of about 80
kilometers (50 miles).
As you can see in Figure 1–16, two gases—nitrogen and oxygen—make up 99 percent of the volume of
clean, dry air. Although these gases are the most plentiful components of the atmosphere and are of
great significance to life on Earth, they are of little or no importance in affecting weather phenomena. The remaining 1 percent of dry air is mostly the inert gas argon (0.93 percent) plus tiny quantities of a
number of other gases.
Carbon Dioxide
Carbon dioxide, although present in only minute amounts (0.0391 percent, or 391 parts per million), is
nevertheless a meteorologically important constituent of air. Carbon dioxide is of great interest to
meteorologists because it is an efficient absorber of energy emitted by Earth and thus influences the
heating of the atmosphere. Although the proportion of carbon dioxide in the atmosphere is relatively
Chapter 1 Introduction to the Atmosphere 17
18 The Atmosphere: An Introduction to Meteorology
Box 1–2 The Carbon Cycle: One of Earth’s Subsystems
To illustrate the movement of material and energy in the Earth system, let us take a brief look at the
carbon cycle (Figure 1–C). Pure carbon is relatively rare in nature. It
is found predominantly in two minerals: diamond and graphite. Most carbon is bonded chemically to
other elements to
form compounds such as carbon dioxide, calcium carbonate, and the hydrocarbons found in coal and
petroleum. Carbon is also the basic building block of life as it readily combines with hydrogen and
oxygen to form the fundamental organic compounds that compose living things.
In the atmosphere, carbon is found mainly as carbon dioxide (CO2). Atmospheric carbon dioxide is
significant because it is a greenhouse gas, which means it is an efficient absorber of energy emitted by
Earth and thus influences the heating of the atmosphere. Because
many of the processes that operate on
Earth involve carbon dioxide, this gas
is constantly moving into and out of the atmosphere. For example, through the process of
photosynthesis, plants absorb carbon dioxide from the atmosphere to produce the essential organic
compounds needed for growth. Animals that consume these plants (or consume other animals that eat
plants) use these organic compounds as a source of energy and, through the process
FIGURE 1–C Simplified diagram of the carbon cycle, with emphasis on the flow of carbon between the
atmosphere and the hydrosphere, geosphere, and biosphere. The colored arrows show whether the
flow of carbon is into or out of the atmosphere.
Burning and decay of biomass
Photosynthesis by vegetation
Burial of biomass
Photosynthesis and respiration of marine organisms Deposition of carbonate sediments
CO2 dissolves in seawater
Weathering of carbonate rock
Volcanic activity
Weathering of granite
Respiration by land organisms
Burning of fossil fuels
Lithosphere
Sediment and sedimentary rock
CO2 entering the atmosphere
CO2 leaving the atmosphere
Carbon dioxide (0.0391% or 391 ppm)
Nitrogen (78.084%)
1.5 Krypton (Kr) 1.14
of respiration, return carbon dioxide to the atmosphere. (Plants also return some CO2 to the
atmosphere via respiration.) Further,
when plants die and decay or are burned, this biomass is oxidized, and carbon dioxide is returned to the
atmosphere.
Methane (CH4)
Concentration in parts per million (ppm)
uniform, its percentage has been rising steadily for more than a century. Figure 1–17 is a graph showing
the growth in atmospheric CO2 since 1958. Much of this rise is attributed to the burning of everincreasing
quantities of fossil fuels, such as coal and oil. Some of this additional carbon dioxide is
absorbed by the waters of the ocean or is used by plants, but more than 40 percent remains in the air.
Estimates pro- ject that by sometime in the second half of the twenty- first century, carbon dioxide
levels will be twice as high as pre-industrial levels.
Most atmospheric scientists agree that increased carbon dioxide concentrations have contributed to a
warming of Earth’s atmosphere over the past several decades and will continue to do so in the decades
to come. The magnitude of such temperature changes is uncertain and depends partly on the quantities of CO2 contributed by human activities in the years ahead. The role of carbon dioxide in the atmosphere
and its possible effects on climate are examined in more detail in Chapters 2 and 14.
Argon (0.934%)
All others
Oxygen (20.946%)
18.2
Neon (Ne)
Helium (He) 5.24
Hydrogen (H ) 0.5 2
Figure 1–16 Proportional volume of gases composing dry air. Nitrogen and oxygen obviously dominate.
Chapter 1 Introduction to the Atmosphere 19
Not all dead plant material decays immediately back to carbon dioxide. A small percentage is deposited
as sediment. Over long spans of geologic time, considerable biomass is buried with sediment. Under the
right conditions, some of these carbon-rich deposits are converted to fossil fuels—coal, petroleum, or
natural gas. Eventually some
of the fuels are recovered (mined or pumped from a well) and burned to run factories and fuel our
transportation system. One result of fossil-fuel combustion is the release of huge quantities of CO2 into
the atmosphere. Certainly one of the most active parts of the carbon cycle is the movement of CO2 from
the atmosphere to the biosphere and back again.
Carbon also moves from the geosphere and hydrosphere to the atmosphere and back again. For
example, volcanic activity early in Earth’s history is thought to be
the source of much of the carbon dioxide found in the atmosphere. One way that carbon dioxide makes
its way back to the hydrosphere and then to the solid Earth
is by first combining with water to form carbonic acid (H2CO3), which then attacks the rocks that
compose the geosphere. One product of this chemical weathering
of solid rock is the soluble bicarbonate
ion (2HCO3–), which is carried by groundwater and streams to the ocean. Here water-dwelling
organisms extract this dissolved material to produce hard parts (shells) of calcium carbonate (CaCO3).
When the organisms die, these skeletal
remains settle to the ocean floor as biochemical sediment and become sedimentary rock. In fact, the
geosphere is by far Earth’s largest depository of carbon, where it is a constituent of a variety of rocks,
the most abundant being limestone (Figure 1–D). Eventually the limestone
may be exposed at Earth’s surface, where chemical weathering will cause the carbon stored in the rock
to be released to the atmosphere as CO2. 390 380 370 360 350 340 330 320
In summary, carbon moves among all four of Earth’s major spheres. It is essential to every living thing in
the biosphere. In the atmosphere carbon dioxide is an important greenhouse gas. In the hydrosphere,
carbon dioxide is dissolved in lakes, rivers, and the ocean. In the geosphere, carbon is contained in
carbonate-rich sediments and sedimentary rocks and is stored as organic matter dispersed through
sedimentary rocks and as deposits of coal and petroleum.
FIGURE 1–D
A great deal of carbon is
locked up in Earth’s geosphere.
England’s White Chalk Cliffs are an example.
Chalk is a soft, porous type of limestone (CaCO3) consisting mainly of the hard parts of microscopic
organisms called coccoliths (inset). (Photo by Prisma/SuperStock; inset by Steve Gschmeissner/Photo
Researchers, Inc.)
Variable Components
Air includes many gases and particles that vary significantly from time to time and place to place.
Important examples include water vapor, aerosols, and ozone. Although usually present in small
percentages, they can have significant ef- fects on weather and climate.
Water Vapor The amount of water vapor in the air var- ies considerably, from practically none at all up
to about 4 percent by volume. Why is such a small fraction of the
Figure 1–17 Changes in the atmosphere’s carbon dioxide (CO2) as measured at Hawaii’s Mauna Loa
Observatory. The oscillations reflect the seasonal variations in plant growth and decay in the Northern
Hemisphere. During the first 10 years of this record (1958–1967), the average yearly CO2 increase was
0.81 ppm. During the last 10 years (2001–2010) the average yearly increase was 2.04 ppm. (Data from
NOAA)
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
CO2 concentration (ppm)
20 The Atmosphere: An Introduction to Meteorology
Box 1–3 Origin and Evolution of Earth’s Atmosphere
The air we breathe is a stable mixture of 78 percent nitrogen, 21 percent oxygen, nearly 1 percent argon,
and small amounts of gases such as carbon dioxide and water vapor. However, our planet’s original
atmosphere 4.6 billion years ago was substantially different. Earth’s Primitive Atmosphere
Early in Earth’s formation, its atmosphere likely consisted of gases most common in the early solar
system: hydrogen, helium, methane, ammonia, carbon dioxide, and water vapor. The lightest of these
gases, hydrogen and helium, escaped into space because Earth’s gravity was too weak to hold them.
Most of the remaining gases were probably scattered into space by strong solar winds (vast streams of
particles) from a young active Sun. (All stars, including the Sun, apparently experience a highly active
stage early in their evolution, during which solar winds are very intense.)
Earth’s first enduring atmosphere was generated by a process called outgassing, through which gases
trapped in the planet’s interior are released. Outgassing from hundreds of active volcanoes still remains
an important planetary function worldwide (Figure 1–E). However, early in Earth’s history, when
massive heating and fluid-like motion occurred in the planet’s interior, the
gas output must have been immense. Based on our understanding of modern volcanic eruptions, Earth’s
primitive atmosphere probably consisted of mostly water vapor,
carbon dioxide, and sulfur dioxide, with minor amounts of other gases and minimal nitrogen. Most
importantly, free oxygen was not present.
atmosphere so significant? The fact that water vapor is the source of all clouds and precipitation would
be enough to ex- plain its importance. However, water vapor has other roles. Like carbon dioxide, it has
the ability to absorb heat given off by Earth, as well as some solar energy. It is therefore impor-tant
when we examine the heating of the atmosphere.
When water changes from one state to another, such as from a gas to a liquid or a liquid to a solid (see
Figure 4–3,
Students Sometimes Ask…
Could you explain a little more about why the graph in
Figure 1–17 has so many ups and downs?
Sure. Carbon dioxide is removed from the air by photosynthesis, the process by which green plants
convert sunlight into chemical energy. In spring and summer, vigorous plant growth in the extensive
land areas of the Northern Hemisphere removes carbon dioxide from the atmosphere, so the graph
takes a dip. As winter approaches, many plants die or shed leaves. The decay of organic matter returns
carbon dioxide to the air, causing the graph to spike upward.
p. 99), it absorbs or releases heat. This energy is termed latent heat, which means hidden heat. As you
will see in later chapters, water vapor in the atmosphere transports this latent heat from one region to
another, and it is the energy source that drives many storms.
Aerosols The movements of the atmosphere are sufficient to keep a large quantity of solid and liquid
particles sus- pended within it. Although visible dust sometimes clouds the sky, these relatively large particles are too heavy to stay in the air very long. Still, many particles are microscopic and remain
suspended for considerable periods of time. They may originate from many sources, both natural and
human made, and include sea salts from breaking waves, fine soil blown into the air, smoke and soot
from fires, pollen and mi- croorganisms lifted by the wind, ash and dust from volcanic eruptions, and
more (Figure 1–18a). Collectively, these tiny solid and liquid particles are called aerosols.
Aerosols are most numerous in the lower atmosphere near their primary source, Earth’s surface.
Nevertheless, the upper atmosphere is not free of them, because some dust is
FIGURE 1–E Earth’s first enduring atmosphere was formed by a process called outgassing, which
continues today, from hundreds of active volcanoes worldwide. (Photo by Greg Vaughn/Alamy)
Oxygen in the Atmosphere
As Earth cooled, water vapor condensed
to form clouds, and torrential rains began
to fill low-lying areas, which became the oceans. In those oceans, nearly 3.5 billion years ago,
photosynthesizing bacteria began to release oxygen into the water. During photosynthesis, organisms
use the Sun’s energy to produce organic material (energetic molecules of sugar containing hydrogen and
carbon) from carbon dioxide (CO2) and water (H2O). The first bacteria probably used hydrogen sulfide
(H2S) as the source of hydrogen rather than water. One of the earliest bacteria, cyanobacteria (once
called blue-green algae), began to produce oxygen as a by-product of photosynthesis.
Initially, the newly released oxygen was readily consumed by chemical reactions with other atoms and
molecules (particularly iron) in the ocean (Figure 1–F). Once the available iron satisfied its need for
oxygen and as the number of oxygen-generating organisms increased, oxygen began to build in the
atmosphere. Chemical analyses of rocks suggest that a significant amount
of oxygen appeared in the atmosphere as early as 2.2 billion years ago and increased steadily until it
reached stable levels about 1.5 billion years ago. Obviously, the availability of free oxygen had a major
impact on the development of life and vice versa. Earth’s atmosphere evolved together with its lifeforms
from an oxygen-free envelope to an oxygen-rich environment.
FIGURE 1–F These ancient layered, iron-rich rocks, called banded iron formations, were deposited during
a geologic span known as the Precambrian. Much of the oxygen generated as a by-product of
photosynthesis was readily consumed by chemical reactions with iron to produce these rocks. (Photo by
John Cancalosi/Photolibrary)
Chapter 1 Introduction to the Atmosphere 21
carried to great heights by rising currents of air, and other particles are contributed by meteoroids that
disintegrate as they pass through the atmosphere.
From a meteorological standpoint, these tiny, often invisible particles can be significant. First, many act
as sur- faces on which water vapor may condense, an important function in the formation of clouds and fog. Second, aero-sols can absorb or reflect incoming solar radiation. Thus, when an air-pollution
episode is occurring or when ash fills the sky following a volcanic eruption, the amount of sun- light
reaching Earth’s surface can be measurably reduced. Finally, aerosols contribute to an optical
phenomenon we have all observed—the varied hues of red and orange at sunrise and sunset (Figure 1–
18b).
Ozone Another important component of the atmosphere is ozone. It is a form of oxygen that combines
three oxygen atoms into each molecule (O3). Ozone is not the same as the oxygen we breathe, which
has two atoms per molecule (O2). There is very little ozone in the atmosphere. Overall, it rep-resents
just 3 out of every 10 million molecules. Moreover,
its distribution is not uniform. In the lowest portion of the atmosphere, ozone represents less than 1
part in 100 million. It is concentrated well above the surface in a layer called the stratosphere, between
10 and 50 kilometers (6 and 31 miles).
In this altitude range, oxygen molecules (O2) are split into single atoms of oxygen (O) when they absorb
ultraviolet radiation emitted by the Sun. Ozone is then created when a single atom of oxygen (O) and a
molecule of oxygen (O2) collide. This must happen in the presence of a third, neu-tral molecule that
acts as a catalyst by allowing the reaction to take place without itself being consumed in the process.
Ozone is concentrated in the 10- to 50-kilometer height range because a crucial balance exists there:
The ultraviolet radia-tion from the Sun is sufficient to produce single atoms of oxygen, and there are
enough gas molecules to bring about the required collisions.
The presence of the ozone layer in our atmosphere is crucial to those of us who are land dwellers. The
reason is that ozone absorbs the potentially harmful ultraviolet (UV) radiation from the Sun. If ozone did
not filter a great deal of the ultraviolet radiation, and if the Sun’s UV rays reached
Another significant benefit of the “oxygen explosion” is that oxygen molecules (O2) readily absorb
ultraviolet radiation and rearrange themselves to form ozone (O3). Today, ozone is concentrated above
the surface in a layer called the stratosphere, where it absorbs much of the ultraviolet radiation that
strikes the upper atmosphere.
For the first time, Earth’s surface was protected from this type of solar radiation, which is particularly
harmful to DNA. Marine organisms had always been shielded from ultraviolet radiation by
the oceans, but the development of the atmosphere’s protective ozone layer made the continents
more hospitable.
22
The Atmosphere: An Introduction to Meteorology
(a)
(b)
Dust storm Air pollution
(a) This satellite image from November 11, 2002, shows two examples of aerosols. First, a large dust
storm is blowing across northeastern China toward the Korean Peninsula. Second, a dense haze toward
the south (bottom center) is human-generated air pollution. (b) Dust in the air can cause sunsets to be
especially colorful. (Satellite image courtesy of NASA; photo by elwynn/ Shutterstock)
Figure 1–18
the surface of Earth undiminished, land areas on our planet would be uninhabitable for most life as we
know it. Thus, anything that reduces the amount of ozone in the atmo-sphere could affect the wellbeing
of life on Earth. Just such a problem is described in the next section.
Concept Check 1.6
 1 Is air a specific gas? Explain.
 2 What are the two major components of clean, dry air? What proportion does each represent?
 3 Why are water vapor and aerosols important constituents of Earth’s atmosphere?
 4 What is ozone? Why is ozone important to life on Earth?
Ozone Depletion—
A Global Issue
The loss of ozone high in the atmosphere as a consequence of human activities is a serious global-scale
environmental problem. For nearly a billion years Earth’s ozone layer has
protected life on the planet. However, over the past half cen-tury, people have unintentionally placed
the ozone layer in jeopardy by polluting the atmosphere. The most significant of the offending chemicals
are known as chlorofluorocarbons (CFCs). They are versatile compounds that are chemically stable,
odorless, nontoxic, noncorrosive, and inexpensive to produce. Over several decades many uses were
developed for CFCs, including as coolants for air-conditioning and refrigeration equipment, as cleaning
solvents for electronic components, as propellants for aerosol sprays, and in the production of certain
plastic foams.
Students Sometimes Ask…
Isn’t ozone some sort of pollutant?
Yes, you’re right. Although the naturally occurring ozone in the stratosphere is critical to life on Earth, it
is regarded as a pollutant when produced at ground level because it can damage vegetation and be
harmful to human health. Ozone is a major component
in a noxious mixture of gases and particles called photochemical smog. It forms as a result of reactions
triggered by sunlight that occur among pollutants emitted by motor vehicles and industries. Chapter 13
provides more information about this. No one worried about how CFCs might affect the atmo-sphere until three scientists, Paul Crutzen, F.
Sherwood Rowland, and Mario Molina, studied the relationship. In 1974 they alerted the world when
they reported that CFCs were probably reducing the average concentration of ozone in the stratosphere.
In 1995 these scientists were awarded the Nobel Prize in chemistry for their pioneering work.
They discovered that because CFCs are practically inert (that is, not chemically active) in the lower
atmosphere, a portion of these gases gradually makes its way to the ozone layer, where sunlight
separates the chemicals into their constituent atoms. The chlorine atoms released this way, through a
complicated series of reactions, have the net effect of removing some of the ozone.
The Antarctic Ozone Hole
Although ozone depletion by CFCs occurs worldwide, mea-surements have shown that ozone
concentrations take an especially sharp drop over Antarctica during the Southern Hemisphere spring
(September and October). Later, during November and December, the ozone concentration recovers to
more normal levels (Figure 1–19). Between 1980, when it was discovered, and the early 2000s, this wellpublicized
ozone hole intensified and grew larger until it covered an area roughly the size of North
America (Figure 1–20).
The hole is caused in part by the relatively abundant ice particles in the south polar stratosphere. The ice
boosts the effectiveness of CFCs in destroying ozone, thus caus- ing a greater decline than would
otherwise occur. The zone
of maximum depletion is confined to the Antarctic region by a swirling upper-level wind pattern. When
this vortex weakens during the late spring, the ozone-depleted air is no longer restricted and mixes
freely with air from other lati-tudes where ozone levels are higher.
A few years after the Antarctic ozone hole was discov- ered, scientists detected a similar but smaller
ozone thin- ning in the vicinity of the North Pole during spring and early summer. When this pool breaks
up, parcels of ozone- depleted air move southward over North America, Europe, and Asia.
Effects of Ozone Depletion
Because ozone filters out most of the damaging UV radia-tion in sunlight, a decrease in its
concentration permits more of these harmful wavelengths to reach Earth’s surface. What are the effects
of the increased ultraviolet radiation? Each 1 percent decrease in the concentration of stratospheric
ozone increases the amount of UV radiation that reaches Earth’s surface by about 2 percent. Therefore,
because ul-traviolet radiation is known to induce skin cancer, ozone depletion seriously affects human
health, especially among fair-skinned people and those who spend considerable time in the sun.
The fact that up to a half million cases of these cancers occur in the United States annually means that
ozone deple-tion could ultimately lead to many thousands more cases each year.* In addition to raising
the risk of skin cancer, an increase in damaging UV radiation can negatively impact the human immune
system, as well as promote cataracts, a clouding of the eye lens that reduces vision and may cause
blindness if not treated. The effects of additional UV radiation on animal and plant life are also important. There is serious
concern that crop yields and quality will be adversely affected. Some scientists also fear that increased
UV radiation in the Ant- arctic will penetrate the waters surrounding the continent and impair or destroy
the microscopic plants, called phy-toplankton, that represent the base of the food chain. A decrease in
phytoplankton, in turn, could reduce the popu- lation of copepods and krill that sustain fish, whales,
pen- guins, and other marine life in the high latitudes of the Southern Hemisphere.
Montreal Protocol
What has been done to protect the atmosphere’s ozone layer? Realizing that the risks of not curbing
CFC emissions were difficult to ignore, an international agreement known as the Montreal Protocol on
Substances That Deplete the Ozone Layer was concluded under the auspices of the United Nations in
late 1987. The protocol established legally binding controls
* For more on this, see Severe and Hazardous Weather: “The Ultraviolet Index,” p. 49.
Chapter 1 Introduction to the Atmosphere 23
30
25
20
15
10
5
Area of North
America
Extent of 2006
ozone hole
Extent 2010 ozone
h
of ole
Aug Sep
Oct Nov Dec
Figure 1-19 Changes in the size of the Antarctic ozone hole during 2006 and 2010. The ozone hole in
both years began
to form in August and was well developed in September and October. As is typical, each year the ozone hole persisted through November and disappeared in December. At its maximum, the area of the ozone
hole was about 22 million square kilometers in 2010, an area nearly as large as all of North America.
Million square kilometers
24 The Atmosphere: An Introduction to Meteorology
Area of North Americ
Extent
Area of Antarctica
ozone hole
of
1979
Ozone (Dobson Units) 110 220 330 440 550
30 25a 20
15
10
5
1980 1985 1990 1995 2000 2005 2010 2015
2010 Year
The two satellite images show ozone distribution in the Southern Hemisphere on the days in September
1979 and 2010 when the ozone hole was largest. The dark blue shades over Antarctica correspond to
the region with the sparsest ozone. The ozone hole is not technically a “hole” where no ozone is present
but is actually a region of exceptionally depteted ozone in
the stratosphere over the Antarctic that occurs in the spring. The small graph traces changes in the
maximum size of the ozone hole, 1980–2010. (NOAA)
Figure 1–20
on the production and consumption of gases known to cause ozone depletion. As the scientific
understanding of ozone depletion improved after 1987 and substitutes and alternatives became
available for the offending chemicals, the Montreal Protocol was strengthened several times. More than
190 nations eventually ratified the treaty.
The Montreal Protocol represents a positive international response to a global environment problem. As
a result of the action, the total abundance of ozone-depleting gases in the atmosphere has started to decrease in recent years. Accord- ing to the U.S. Environmental Protection Agency (U.S. EPA), the ozone
layer has not grown thinner since 1998 over most of the world.* If the nations of the world continue to
follow the provisions of the protocol, the decreases are expected to continue throughout the twenty –
first century. Some offend- ing chemicals are still increasing but will begin to decrease in coming
decades. Between 2060 and 2075, the abundance of ozone-depleting gases is projected to fall to values
that exist- ed before the Antarctic ozone hole began to form in the 1980s.
Concept Check 1.7
 1 What are CFCs, and what is their connection to the ozone
 problem?
 2 During what time of year is the Antarctic ozone hole well developed?
 3 Describe three effects of ozone depletion.
 4 What is the Montreal Protocol?
* U.S. EPA, Achievements in Stratospheric Ozone Protection, Progress Report. EPA-430-R-07-001, April
2007, p. 5.
Vertical Structure of the Atmosphere
ATMOSPHERE
Introduction to the Atmosphere
▸Extent of the Atmosphere/Thermal Structure of the Atmosphere
To say that the atmosphere begins at Earth’s surface and ex-tends upward is obvious. However, where
does the atmo-sphere end and where does outer space begin? There is no sharp boundary; the
atmosphere rapidly thins as you travel away from Earth, until there are too few gas molecules to detect.
Pressure Changes
To understand the vertical extent of the atmosphere, let us examine the changes in atmospheric
pressure with height. Atmospheric pressure is simply the weight of the air above. At sea level the
average pressure is slightly more than 1000 millibars. This corresponds to a weight of slightly more than
1 kilogram per square centimeter (14.7 pounds per square inch). Obviously, the pressure at higher
altitudes is less (Figure 1–21).
One-half of the atmosphere lies below an altitude of 5.6 kilometers (3.5 miles). At about 16 kilometers
(10 miles), 90 percent of the atmosphere has been traversed, and above 100 kilometers (62 miles) only
0.00003 percent of all the gases composing the atmosphere remain.
At an altitude of 100 kilometers the atmosphere is so thin that the density of air is less than could be
found in the most perfect artificial vacuum at the surface. Nevertheless, the atmosphere continues to
even greater heights. The truly Million square kilometers
Chapter 1 Introduction to the Atmosphere 25
Kathy Orr, Broadcast Meteorologist
KATHY ORR is an award-winning broadcast meteorologist in Philadelphia. (Photo courtesy of Kathy Orr)
not the ‘rip and read’ of years gone by. We take data from the supercomputers in Wash- ington or
models by the Navy and make our own forecasts. There are some services that provide forecasts locally
and nationally, but they’re not located where we are. I can look out the window and tell whether those
fore- casts are going to be accurate or not.”
As a weathercaster, Orr has worked to promote education in science and math. For three years, she led
a community program called Kidcasters. By offering children a chance to present the weather on TV, Orr
hoped to interest elementary school children in science and math. For the past nine sum- mers, she has
conducted a similar program called Orr at the Shore. Each program highlights environmental issues
along the New Jersey coast.
My job is to explain complicated ideas to people in an uncomplicated way.
Orr continues to promote science literacy by volunteering for the American Meteoro- logical Society’s
DataStreme Atmosphere Project. As a DataStreme mentor, she has vis- ited dozens of schools to train
teachers in the science of meteorology. The teachers then promote the use of weather lessons in their
districts to pique student interest in science, mathematics, and technology. Orr considers her forecasts
educational as well. “My job is to explain complicated ideas to people in an uncomplicated way.”
Being a weathercaster, Orr says, is demanding but also exhilarating. “In TV,
the hours are crazy. If you work mornings, you’re up at 2 AM; if nights, you’re up until midnight. So you
really have to love it. But if you do, you’ll find a way. And I feel blessed to have done this for so long.”
Kathy Orr is a trusted and familiar face
on the airwaves of Philadelphia. As chief meteorologist for CBS3, Orr has kept the City of Brotherly Love
abreast of the weather for 18 years and earned 10 regional Emmy awards in the process.
Orr calls being a television weathercaster a dream come true.
Orr calls being a television weather- caster a dream come true. Growing up in Syracuse, New York, Orr
operated her own miniature weather station and marveled at the snow squalls that howled across Lake
Ontario. “It could be a sunny afternoon, then the wind would blow over the lake. All of
a sudden there was a blinding blizzard,” she says.
When not watching the skies, Orr stayed glued to her family’s TV set. At the time, she couldn’t see how to combine her two major interests. “There weren’t any women doing the weather on
television back then. There were also not a lot of meteorologists on TV; it was less about the science and
more for comic relief,” she says.
She majored in broadcasting at Syracuse University and went on to earn a second degree in
meteorology at the State University of New York at Oswego. There she learned the basis for the snow
squalls that transfixed her as a girl. “These kinds of phenomena are associated with being on the
downwind side of a Great Lake. When wind comes along, the lake acts like a snowmaking machine.”
While still in school, Orr landed a job as
the weathercaster on a Syracuse station’s brand-new morning show. She’s remained a television
meteorologist ever since.
Today, Orr says, being a trained meteorol- ogist “is definitely a competitive advantage. It’s
rarefied nature of the outer atmosphere is described very well by Richard Craig:
The earth’s outermost atmosphere, the part above a few hundred kilometers, is a region of extremely
low density. Near sea level, the number of atoms and molecules in a cubic centimeter of air is about 2 3
1019; near 600 km, it is only about 2 3 107, which is the sea-level value divided by a million million. At
sea level, an atom or molecule can be expected, on the average, to move about 7 3 1026 cm before
colliding with another particle; at the 600-km level, this distance, called the “mean free path,” is about
10 km. Near
sea level, an atom or molecule, on the average, undergoes about 7 3 109 such collisions each second;
near 600 km, this number is reduced to about 1 each minute.*
The graphic portrayal of pressure data (Figure 1–21) shows that the rate of pressure decrease is not
constant. Rather, pressure decreases at a decreasing rate with an increase in altitude until, beyond an
altitude of about 35 kilometers (22 miles), the decrease is negligible.
*Richard Craig, The Edge of Space: Exploring the Upper Atmosphere (New York: Doubleday & Company,
Inc., 1968), p. 130.
26
The Atmosphere: An Introduction to Meteorology
36 32 28 24 20 16 12
8 4
lies below
22 20 18 16 14 12 10 8 6 4 2
Cap t. Kittinger, USAF
1961 31. (102,800
Air press
Air pressure at top of Mt. Evere
(29,035 ft) is
314 m
b
3 km ft)
ure = 9.6
st
atm this
50% of
osphere altitude
mb
200
400
Pressure (mb)
1000
This jet is cruising at an altitude of 10 kilometers (6.2 miles). (Photo by inter- light/Shutterstock)
Question 1 Refer to the graph in Figure 1–21. What is the approximate air pressure where the jet is
flying?
Question 2 About what percentage of the atmosphere is below the jet (assuming that the pressure at
the surface is 1000 millibars)?
Although measurements had not been taken above a height of about 10 kilometers (6 miles), scientists
believed that the temperature continued to decline with height to a value of absolute zero (–273°C) at
the outer edge of the atmo-sphere. In 1902, however, the French scientist Leon Philippe Teisserenc de
Bort refuted the notion that temperature Figure 1–22 Temperatures drop with an increase in altitude in the troposphere. Therefore, it is possible
to have snow on a mountaintop and warmer, snow-free lowlands below. (Photo by David Wall/Alamy)
600 800
Figure 1–21 Atmospheric pressure changes with altitude.
The rate of pressure decrease with an increase in altitude is not constant. Rather, pressure decreases
rapidly near Earth’s surface and more gradually at greater heights.
Put another way, data illustrate that air is highly compressible—that is, it expands with decreasing
pressure and becomes compressed with increasing pressure. Conse- quently, traces of our atmosphere
extend for thousands of kilometers beyond Earth’s surface. Thus, to say where the atmosphere ends
and outer space begins is arbitrary and, to a large extent, depends on what phenomenon one is study –
ing. It is apparent that there is no sharp boundary.
In summary, data on vertical pressure changes show that the vast bulk of the gases making up the
atmosphere is very near Earth’s surface and that the gases gradually merge with the emptiness of space.
When compared with the size of the solid Earth, the envelope of air surrounding our planet is indeed
very shallow.
Temperature Changes
By the early twentieth century much had been learned about the lower atmosphere. The upper
atmosphere was partly known from indirect methods. Data from balloons and kites had revealed that
the air temperature dropped with increas- ing height above Earth’s surface. This phenomenon is felt by
anyone who has climbed a high mountain and is obvious in pictures of snow-capped mountaintops rising
above snow- free lowlands (Figure 1–22).
Altitude (km)
Altitude (miles)
decreases continuously with an increase in altitude. In studying the results of more than 200 balloon
launchings, Teisserenc de Bort found that the temperature stopped decreas- ing and leveled off at an
altitude between 8 and 12 kilometers (5 and 7.5 miles). This sur- prising discovery was at first doubted,
but subsequent data-gathering confirmed his findings. Later, through the use of balloons and rocketsounding
techniques, the temper- ature structure of the atmosphere up to great heights became clear.
Today the atmosphere is divided vertically into four layers on the basis of temperature (Figure 1–23).
Troposphere The bottom layer in which we live, where temperature decreases with an increase in
altitude, is the troposphere. The term was coined in 1908 by Teisserrenc de Bort and literally means the
region where air “turns over,” a reference to the apprecia- ble vertical mixing of air in this lowermost
zone.
140 130 120 110 100 90 80 70 60 50 40 30 20 10
Aurora
Meteor
THERMOSPHERE
Mesopause
MESOSPHERE
Stratopause
STRATOSPHERE
Tropopause
TROPOSPHERE
10 20 30 30
90
80
70
60
50
40
30
20
10
50 ̊C
Chapter 1 Introduction to the Atmosphere
27
Maximum ozone
The temperature decrease in the troposphere
is called the environmental lapse
rate. Its average value is 6.5°C per kilome-ter (3.5°F per 1000 feet), a figure known as
the normal lapse rate. It should be emphasized,
however, that the environmental
lapse rate is not a constant but rather can be
highly variable and must be regularly measured.
To determine the actual environmental
lapse rate as well as gather information
about vertical changes in air pressure, wind,
and humidity, radiosondes are used. A radiosonde is an instrument package that is attached to a
balloon and trans- mits data by radio as it ascends through the atmosphere (Figure 1–24). The
environmental lapse rate can vary dur- ing the course of a day with fluctuations of the weather, as well
as seasonally and from place to place. Sometimes shallow layers where temperatures actually increase
with height are observed in the troposphere. When such a rever-sal occurs, a temperature inversion is
said to exist.*
The temperature decrease continues to an average height of about 12 kilometers (7.5 miles). Yet the
thick- ness of the troposphere is not the same everywhere. It reaches heights in excess of 16 kilometers
(10 miles) in the tropics, but in polar regions it is more subdued, extend- ing to 9 kilometers (5.5 miles)
or less (Figure 1–25). Warm surface temperatures and highly developed thermal mix- ing are responsible
for the greater vertical extent of the tro- posphere near the equator. As a result, the environmental
lapse rate extends to great heights; and despite relatively high surface temperatures below, the lowest
tropospheric temperatures are found aloft in the tropics and not at the poles.
*Temperature inversions are described in greater detail in Chapter 13.
Mt. Everest
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
–140 –120 –100 –80 –60 –40 –20 0 20 40 60 80 100 120 ̊F 32
Temperature
Figure 1–23 Thermal structure of the atmosphere.
The troposphere is the chief focus of meteorologists because it is in this layer that essentially all
important weather phenomena occur. Almost all clouds and certainly all precipitation, as well as all our
violent storms, are born in this lowermost layer of the atmosphere. This is why the troposphere is often
called the “weather sphere.”
Stratosphere Beyond the troposphere lies the stratosphere; the boundary between the troposphere
and the stratosphere is known as the tropopause. Below the tropopause, atmospheric properties are
readily transferred by large-scale turbulence and mixing, but above it, in the stratosphere, they are not. In the stratosphere, the tempera-ture at first remains nearly constant to a height of about 20 kilometers
(12 miles) before it begins a sharp increase that continues until the stratopause is encountered at a
height of about 50 kilometers (30 miles) above Earth’s surface. Higher temperatures occur in the
stratosphere because it is in this layer that the atmosphere’s ozone is concentrated. Recall that ozone
absorbs ultraviolet radiation from the Sun. Con-sequently, the stratosphere is heated by the Sun.
Although the maximum ozone concentration exists between 15 and 30 kilometers (9 and 19 miles), the
smaller amounts of ozone above this height range absorb enough UV energy to cause the higher
observed temperatures.
Height (km)
Height (miles)
Temperature
28 The Atmosphere: An Introduction to Meteorology
Pole
Tropopause
Tropical tropopause
Middle latitude
tropopause
Polar tropopause
Equator
30 27 24 21 18 15 12
9 6 3 0
–70 –60 –50 –40 –30 –20 –10 Temperature ( ̊C)
0 10 20
Figure 1–24 A lightweight instrument package, the radiosonde, is suspended below a 2-meter-wide
weather balloon. As
the radiosonde is carried aloft, sensors measure pressure, temperature, and relative humidity. A radio
transmitter sends the measurements to a ground receiver. By tracking the radiosonde
in flight, information on wind speed and direction aloft is also obtained. Observations where winds aloft
are obtained are called “rawinsonde” observations. Worldwide, there are about 900 upper-air
observation stations. Through international agreements, data are exchanged among countries. (Photo
by Mark Burnett/ Photo Researchers, Inc.) Mesosphere In the third layer, the mesosphere, temper- atures again decrease with height until at the
mesopause, some 80 kilometers (50 miles) above the surface, the aver- age temperature approaches
290°C (2130°F). The coldest temperatures anywhere in the atmosphere occur at the me-sopause. The
pressure at the base of the mesosphere is only about one-thousandth that at sea level. At the
mesopause, the atmospheric pressure drops to just one-millionth that at sea level. Because accessibility
is difficult, the mesosphere is one of the least explored regions of the atmosphere. The reason is that it
cannot be reached by the highest-flying airplanes and research balloons, nor is it accessible to the
Figure 1–25 Differences in the height of the tropopause. The variation in the height of the tropopause,
as shown on the small inset diagram, is greatly exaggerated.
lowest-orbiting satellites. Recent technical developments are just beginning to fill this knowledge gap.
Thermosphere The fourth layer extends outward from the mesopause and has no well-defined upper
limit. It is the thermosphere, a layer that contains only a tiny frac- tion of the atmosphere’s mass. In the
extremely rarified air of this outermost layer, temperatures again increase, due to the absorption of very
shortwave, high-energy solar radia-tion by atoms of oxygen and nitrogen.
Temperatures rise to extremely high values of more than 1000°C (1800°F) in the thermosphere. But such
temperatures are not comparable to those experienced near Earth’s sur- face. Temperature is defined in
terms of the average speed at which molecules move. Because the gases of the thermo-sphere are
moving at very high speeds, the temperature is very high. But the gases are so sparse that collectively
they possess only an insignificant quantity of heat. For this reason, the temperature of a satellite
orbiting Earth in the thermosphere is determined chiefly by the amount of solar
Altitude (km)
Chapter 1 Introduction to the Atmosphere 29
radiation it absorbs and not by the high temperature of the almost nonexistent surrounding air. If an
astronaut inside were to expose his or her hand, the air in this layer would not feel hot.
Concept Check 1.8
 1 Does air pressure increase or decrease with an increase in
 altitude? Is the rate of change constant or variable? Explain.
 2 Is the outer edge of the atmosphere clearly defined? Explain.
 3 The atmosphere is divided vertically into four layers on the basis of temperature. List these
layers in order from lowest to highest. In which layer does practically all of our weather occur?
 4 Why does temperature increase in the stratosphere?
 5 Why are temperatures in the thermosphere not strictly
 comparable to those experienced near Earth’s surface? Vertical Variations in Composition
In addition to the layers defined by vertical variations in temperature, other layers, or zones, are also
recognized in the atmosphere. Based on composition, the atmosphere is often divided into two layers:
the homosphere and the heterosphere. From Earth’s surface to an altitude of about 80 kilometers (50
miles), the makeup of the air is uniform in terms of the proportions of its component gases. That is, the
composition is the same as that shown earlier, in Figure 1–16. This lower uniform layer is termed the
homosphere, the zone of homogeneous composition.
In contrast, the very thin atmosphere above 80 kilometers is not uniform. Because it has a
heterogeneous composition, the term heterosphere is used. Here the gases are arranged into four
roughly spherical shells, each with a distinctive composition. The lowermost layer is dominated by
molec- ular nitrogen (N2), next, a layer of atomic oxygen (O) is encountered, followed by a layer
dominated by helium (He) atoms, and finally a region consisting largely of hydrogen (H) atoms. The
stratified nature of the gases making up the heterosphere varies according to their weights. Molecular
nitrogen is the heaviest, and so it is lowest. The lightest gas, hydrogen, is outermost.
Ionosphere
Located in the altitude range between 80 to 400 kilometers (50 to 250 miles), and thus coinciding with
the lower portions of the thermosphere and heterosphere, is an electrically charged layer known as the
ionosphere. Here molecules of nitrogen and atoms of oxygen are readily ionized as they
When this weather balloon was launched, the surface temperature was 17°C. It is now at an altitude of 1
kilometer. (Photo by David R. Frazier/ Photo Researchers, Inc.)
Question 1 What term is applied to the instrument package being car-ried aloft by the balloon?
Question 2 In what layer of the atmosphere is the balloon? Question 3 If average conditions prevail,
what air temperature is the
instrument package recording? How did you figure this out?
Question 4 How will the size of the balloon change, if at all, as it rises through the atmosphere? Explain.
absorb high-energy shortwave solar energy. In this process, each affected molecule or atom loses one or
more electrons and becomes a positively charged ion, and the electrons are set free to travel as electric
currents.
Although ionization occurs at heights as great as 1000 kilometers (620 miles) and extends as low as
perhaps 50 kilometers (30 miles), positively charged ions and nega-tive electrons are most dense in the
range of 80 to 400 kilo- meters (50 to 250 miles). The concentration of ions is not great below this zone
because much of the short-wavelength radiation needed for ionization has already been depleted.
30 The Atmosphere: An Introduction to Meteorology In addition, the atmospheric density at this level results in a large percentage of free electrons being
swiftly cap-tured by positively charged ions. Beyond the 400-kilometer (250-mile) upward limit of the
ionosphere, the concentra-tion of ions is low because of the extremely low density of the air. Because
so few molecules and atoms are present, relatively few ions and free electrons can be produced.
The electrical structure of the ionosphere is not uni- form. It consists of three layers of varying ion
density. From bottom to top, these layers are called the D, E, and F lay- ers, respectively. Because the
production of ions requires direct solar radiation, the concentration of charged parti- cles changes from
day to night, particularly in the D and E zones. That is, these layers weaken and disappear at night and
reappear during the day. The uppermost layer, or F layer, on the other hand, is present both day and
night. The density of the atmosphere in this layer is very low, and positive ions and electrons do not
meet and recombine as rapidly as they do at lesser heights, where density is higher. Consequently, the
concentration of ions and electrons in the F layer does not change rapidly, and the layer, although weak,
remains through the night.
The Auroras
As best we can tell, the ionosphere has little impact on our daily weather. But this layer of the
atmosphere is the site of one of nature’s most interesting spectacles, the auroras (Figure 1–26). The
aurora borealis (northern lights) and
its Southern Hemisphere counterpart, the aurora australis (southern lights), appear in a wide variety of
forms. Some-times the displays consist of vertical streamers in which there can be considerable
movement. At other times the auroras appear as a series of luminous expanding arcs or as a quiet glow
that has an almost foglike quality.
The occurrence of auroral displays is closely correlated in time with solar-flare activity and, in geographic
location, with Earth’s magnetic poles. Solar flares are massive mag- netic storms on the Sun that emit
enormous amounts of energy and great quantities of fast-moving atomic particles. As the clouds of
protons and electrons from the solar storm approach Earth, they are captured by its magnetic field,
which in turn guides them toward the magnetic poles. Then, as the ions impinge on the ionosphere,
they energize the atoms of oxygen and molecules of nitrogen and cause them to emit light—the glow of
the auroras. Because the occur-rence of solar flares is closely correlated with sunspot activ- ity, auroral
displays increase conspicuously at times when sunspots are most numerous.
Concept Check 1.9
1 Distinguish between the homosphere and the heterosphere. 2 What is the ionosphere? Where in the
atmosphere is it located? 3 What is the primary cause of the auroras?
Figure 1–26 Aurora borealis (northern lights) as seen from Alaska. The same phenomenon occurs
toward the South Pole, where it is called the aurora australis (southern lights). (Photo by agefotostock/
SuperStock)
Give It Some Thought 1. Determine which statements refer to weather and which refer to climate. (Note: One
statement includes aspects of both weather and climate.)
2. a. The baseball game was rained out today.
a. January is Omaha’s coldest month.
b. North Africa is a desert.
c. The high this afternoon was 25°C.
d. Last evening a tornado ripped through central Oklahoma.
e. I am moving to southern Arizona because it is warm and sunny.
f. Thursday’s low of –20°C is the coldest temperature ever recorded for that city.
g. It is partly cloudy.
3. After entering a dark room, you turn on a wall switch,
4. but the light does not come on. Suggest at least three hypotheses that might explain this
observation.
5. Making accurate measurements and observations is
a basic part of scientific inquiry. The accompanying radar image, showing the distribution and
intensity
of precipitation associated with a storm, provides
one example. Identify three additional images in this chapter that illustrate ways in which
scientific data are gathered. Suggest advantages that might be associated with each example.
greenhouse gases have increased global average
temperatures.
b. One or two studies suggest that hurricance intensity is increasing.
5. Refer to Figure 1–21 to answer the following questions.
6. If you were to climb to the top of Mount Everest,
7. how many breaths of air would you have to take at
8. that altitude to equal one breath at sea level?
9. If you are flying in a commercial jet at an altitude of 12 kilometers, about what
percentage of the atmosphere’s mass is below you?
6. If you were ascending from the surface of Earth to the top of the atmosphere, which one of the
following would be most useful for determining the layer of the atmosphere you were in? Explain.
a. Doppler radar
b. Hygrometer (humidity)
c. Weather satellited. Barometer (air pressure)
e. Thermometer (temperature)
7. The accompanying photo provides an example of interactions among different parts of the Earth
system. It is a view of a mudflow that was triggered by extraordinary rains. Which of Earth’s four
“spheres” were involved in this natural disaster that buried a small town on the Philippine island of
Leyte? Describe how each contributed to the mudflow.
(Photo by AP Photo/Pat Roque)
8. Where would you expect the thickness of the troposphere (that is, the distance between Earth’s
surface and the tropopause) to be greater: over Hawaii or Alaska? Why? Do you think it is likely that the
thickness of the troposphere over Alaska is different in January than in July? If so, why?
Chapter 1 Introduction to the Atmosphere 31
(Image by National Weather Service)
4. During a conversation with your meteorology professor, she makes the two statements listed below.
Which can be considered a hypothesis? Which is more likely a theory?
a. After several decades, the science community has determined that human-generated
32 The Atmosphere: An Introduction to Meteorology
INTRODUCTION TO THE ATMOSPHERE IN REVIEW
 ● Meteorology is the scientific study of the atmosphere. Weather refers to the state of the
atmosphere at a given time and place. It is constantly changing, sometimes from hour to hour
and other times from day to day. Climate is an aggregate
 of weather conditions, the sum of all statistical weather information that helps describe a place
or region. The
nature of both weather and climate is expressed in terms
of the same basic elements, those quantities or properties measured regularly. The most
important elements are (1) air temperature, (2) humidity, (3) type and amount of cloudiness, (4)
type and amount of precipitation, (5) air pressure, and
 (6) the speed and direction of the wind.
 ● All science is based on the assumption that the natural world
 behaves in a consistent and predictable manner. The process by which scientists gather facts
through observation and careful measurement and formulate scientific hypotheses and theories
is often referred to as the scientific method.  ● Earth’s four spheres include the atmosphere (gaseous envelope), the geosphere (solid Earth),
the hydrosphere (water portion),
and the biosphere (life). Each sphere is composed of many interrelated parts and is intertwined
with all the other spheres.
 ● Although each of Earth’s four spheres can be studied separately, they are all related in a
complex and continuously interacting whole that we call the Earth system. Earth system science
uses an interdisciplinary approach to integrate the knowledge of several academic fields in the
study of our planet and its global environmental problems.
 ● A system is a group of interacting parts that form a complex whole. The two sources of energy
that power the Earth system are (1) the Sun, which drives the external processes that occur in
the atmosphere, hydrosphere, and at Earth’s surface, and (2) heat from Earth’s interior that
powers the internal processes that produce volcanoes, earthquakes, and mountains.
 ● Air is a mixture of many discrete gases, and its composition varies from time to time and
place to place. After water vapor, dust, and other variable components are removed, two gases,
nitrogen and oxygen, make up 99 percent of the volume of the remaining clean, dry air. Carbon
dioxide, although present
 in only minute amounts (0.0391 percent, or 391 ppm), is an efficient absorber of energy emitted
by Earth and thus influences the heating of the atmosphere.
 ● The variable components of air include water vapor, dust particles, and ozone. Like carbon
dioxide, water vapor can absorb heat given off by Earth as well as some solar energy. When
water vapor changes from one state to another, it absorbs or releases heat. In the atmosphere,
water vapor transports this latent (“hidden”) heat from one place
 to another, and it is the energy source that helps drive
many storms. Aerosols (tiny solid and liquid particles) are meteorologically important because
these often-invisible particles act as surfaces on which water can condense and are also
absorbers and reflectors of incoming solar radiation. Ozone, a form of oxygen that combines
three oxygen atoms into each molecule (O3), is a gas concentrated in the 10- to 50-kilometer
height range in the atmosphere that absorbs the potentially harmful ultraviolet (UV) radiation
from the Sun.
● Over the past half century, people have placed Earth’s
ozone layer in jeopardy by polluting the atmosphere with chlorofluorocarbons (CFCs), which remove
some of the gas. Ozone concentrations take an especially sharp drop over Antarctica duri ng the
Southern Hemisphere spring (September and October). Ozone depletion seriously affects human health,
especially among fair-skinned people and those who spend considerable time in the Sun. The Montreal
Protocol, concluded under the auspices of the United Nations, represents a positive international
response to the ozone problem. ● No sharp boundary to the upper atmosphere exists. The atmosphere simply thins as you travel away
from Earth, until there are too few gas molecules to detect. Traces of atmosphere extend for thousands
of kilometers beyond Earth’s surface.
● Using temperature as the basis, the atmosphere is divided into four layers. The temperature decrease
in the troposphere, the bottom layer in which we live, is called the environmental lapse rate. Its average
value is 6.5°C per kilometer, a figure known
as the normal lapse rate. The environmental lapse rate is not a constant and must be regularly
measured using radiosondes. The thickness of the troposphere is generally greater in the tropics than in
polar regions. Essentially all important weather phenomena occur in the troposphere. Beyond the
troposphere lies the stratosphere; the boundary between the troposphere and stratosphere is known as
the tropopause. In the stratosphere, the temperature at first remains constant to a height of about 20
kilometers (12 miles) before it begins a sharp increase due to the absorption of ultraviolet radiation
from the Sun by ozone. The temperatures continue to increase until the stratopause is encountered at a
height of about 50 kilometers (30 miles). In the mesosphere, the third layer, temperatures again
decrease with height until the mesopause, some 80 kilometers (50 miles) above the surface. The fourth
layer, the thermosphere, with no well-defined upper limit, consists of extremely rarefied air.
Temperatures here increase with an increase in altitude.
● The atmosphere is often divided into two layers, based
on composition. The homosphere (zone of homogeneous composition), from Earth’s surface to an
altitude of about
80 kilometers (50 miles), consists of air that is uniform in terms of the proportions of its component
gases. Above 80 kilometers, the heterosphere (zone of heterogenous composition) consists of gases
arranged into four roughly spherical shells, each with a distinctive composition. The stratified nature of
the gases in the heterosphere varies according to their weights.
● Occurring in the altitude range between 80 and 400 kilometers (50 and 250 miles) is an electri cally
charged layer known as the ionosphere. Here molecules of nitrogen and atoms of oxygen are readily
ionized as they absorb high-energy, shortwave solar energy. Three layers of varying ion density make up
the ionosphere. Auroras (the aurora borealis, northern lights, and its Southern Hemisphere counterpart
the aurora australis, southern lights) occur within the ionosphere. Auroras form as clouds of protons
and electrons ejected from the Sun during solar-flare activity enter the atmosphere near Earth’s
magnetic poles and energize the atoms of oxygen and molecules of nitrogen, causing them to emit
light—the glow of the auroras.
aerosols (p. 21)
air (p. 17)
atmosphere (p. 13) aurora australis (p. 29) aurora borealis (p. 29) biosphere (p. 15) climate (p. 5)
elements of weather and climate (p. 7) environmental lapse rate (p. 26) geosphere (p. 13)
hydrosphere (p. 14)
hypothesis (p. 9)
ionosphere (p. 29) mesopause (p. 27) mesosphere (p. 27) meteorology (p. 4) ozone (p. 21)
PROBLEMS
radiosonde (p. 26) stratopause (p. 27) stratosphere (p. 27) system (p. 16) theory (p. 10) thermosphere (p.
27) tropopause (p. 27) troposphere (p. 26) weather (p. 5)
VOCABULARY REVIEW
8. a.
On a spring day a middle-latitude city (about 40°N latitude) has a surface (sea-level) temperature of 10°C.
If vertical soundings reveal a nearly constant environmental lapse rate of 6.5°C per kilometer and a
temperature
at the tropopause of –55°C, what is the height of the tropopause?
Chapter 1 Introduction to the Atmosphere 33
10. Refer to the newspaper-type weather map in Figure 1–3 to answer the following:
a. Estimate the predicted high temperatures in central New York State and the
northwest corner of Arizona.
b. Where is the coldest area on the weather map? Where is the warmest?
c. On this weather map, H stands for the center of a region of high pressure. Does it
appear as though high pressure is associated with precipitation or fair weather?
d. Which is warmer—central Texas or central Maine? Would you normally expect this to
be the case?
11. Refer to the graph in Figure 1–5 to answer the following questions about temperatures in New
York City:
a. What is the approximate average daily high temperature in January? In July?
b. Approximately what are the highest and lowest temperatures ever recorded?
12. Refer to the graph in Figure 1–7. Which year had the greatest number of billion-dollar weather
disasters? How many events occurred that year? In which year was the damage amount
greatest?
13. Refer to the graph in Figure 1–21 to answer the following:
a. Approximately how much does the air pressure drop (in
b. millibars) between the surface and 4 kilometers? (Use a
c. surface pressure of 1000 millibars.)
d. How much does the pressure drop between 4 and 8 e. kilometers?
f. Based on your answers to parts a and b, answer the
g. following: With an increase in altitude, air pressure decreases at a(n) (constant,
increasing, decreasing) rate. Underline the correct answer.
5. If the temperature at sea level were 23°C, what would the air temperature be at a height of 2
kilometers, under average conditions?
6. Use the graph of the atmosphere’s thermal structure (Figure 1–23) to answer the following:
14. What are the approximate height and temperature of the stratopause?
15. At what altitude is the temperature lowest? What is the temperature at that height?
7. Answer the following questions by examining the graph in Figure 1–25:
16. In which one of the three regions (tropics, middle latitudes, poles) is the surface temperature
lowest?
17. In which region is the tropopause encountered at the lowest altitude? The highest? What are
the altitudes and temperatures of the tropopause in those regions?
b. On the same spring day a station near the equator
has a surface temperature of 25°C, 15°C higher than
the middle-latitude city mentioned in part a. Vertical soundings reveal an environmental lapse rate of
6.5°C per kilometer and indicate that the tropopause is encountered at 16 kilometers. What is the air
temperature at the tropopause?
Log in to www.mymeteorologylab.com for animations, videos, MapMaster interactive maps, GEODe
media, In the News RSS feeds, web links, glossary flashcards, self-study quizzes and a Pearson eText
version of this book to enhance your study of Introduction to the Atmosphere.
theory.
 List and describe Earth’s four major spheres.
 Define system and explain why Earth can be thought of as a system.
List the major gases composing Earth’s atmosphere and identify those components that are most
important meteorologically.
Explain why ozone depletion is a significant global issue.
Interpret a graph that shows changes in air pressure from Earth’s surface to the top of the atmosphere.
Sketch and label a graph showing the thermal structure of the atmosphere.
Distinguish between homosphere and heterosphere.
3
4 The Atmosphere: An Introduction to Meteorology Focus on the Atmosphere
everywhere on our planet. The United States likely has the greatest variety of weather of any country in
the world. Severe weather events, such as tornadoes, flash floods, and intense thunderstorms, as well as
hurricanes and bliz-zards, are collectively more frequent and more damaging in the United States than
in any other nation. Beyond its direct impact on the lives of individuals, the weather has a strong effect
on the world economy, by influencing agri- culture, energy use, water resources, transportation, and
industry.
Weather clearly influences our lives a great deal. Yet it is also important to realize that people influence
the atmo-sphere and its behavior as well (Figure 1–2). There are, and will continue to be, significant
political and scientific deci-sions to make involving these impacts. Answers to ques-tions regarding air
pollution and its control and the effects of various emissions on global climate are important exam- ples.
So there is a need for increased awareness and under-standing of our atmosphere and its behavior.
Meteorology, Weather, and Climate
The subtitle of this book includes the word meteorology. Meteorology is the scientific study of the
atmosphere and the phenomena that we usually refer to as weather. Along with geology, oceanography,
and astronomy, meteorology is considered one of the Earth sciences—the sciences that seek to
understand our planet. It is important to point out that there are not strict boundaries among the Earth sciences; in many situations, these sciences overlap. Moreover, all of the Earth sciences involve an
understanding and applica-tion of knowledge and principles from physics, chemistry, and biology. You
will see many examples of this fact in your study of meteorology.
Acted on by the combined effects of Earth’s motions and energy from the Sun, our planet’s formless and
invis- ible envelope of air reacts by producing an infinite variety of weather, which in turn creates the
basic pattern of global climates. Although not identical, weather and climate have much in common.
Weather is constantly changing, sometimes from hour to hour and at other times from day to day. It is a
term that refers to the state of the atmosphere at a given time and place. Whereas changes in the
weather are continuous and sometimes seemingly erratic, it is nevertheless possible to arrive at a
generalization of these variations. Such a descrip-tion of aggregate weather conditions is termed
climate. It is based on observations that have been accumulated over many decades. Climate is often
defined simply as “average weather,” but this is an inadequate definition. In order to accurately portray
the character of an area, variations and extremes must also be included, as well as the probabili-ties
that such departures will take place. For example, it is necessary for farmers to know the average rainfall
during the growing season, and it is also important to know the frequency of extremely wet and
extremely dry years. Thus, climate is the sum of all statistical weather information that helps describe a
place or region.
ATMOSPHERE
Introduction to the Atmosphere ▸Weather and Climate
Weather influences our everyday activities, our jobs, and our health and comfort. Many of us pay little
attention to the weather unless we are inconvenienced by it or when it adds to our enjoyment of
outdoor activities. Nevertheless, there are few other aspects of our physical environment that affect our
lives more than the phenomena we collectively call the weather.
Weather in the United States
The United States occupies an area that stretches from the tropics to the Arctic Circle. It has thousands
of miles of coast- line and extensive regions that are far from the influence of the ocean. Some
landscapes are mountainous, and others are dominated by plains. It is a place where Pacific storms
strike the West Coast, while the East is sometimes influenced by events in the Atlantic and the Gulf of
Mexico. For those in the center of the country, it is common to experience weather events triggered
when frigid southward-bound Canadian air masses clash with northward-moving tropical ones from the
Gulf of Mexico.
Stories about weather are a routine part of the daily news. Articles and items about the effects of heat,
cold, floods, drought, fog, snow, ice, and strong winds are com-monplace (Figure 1–1). Memorable
weather events occur Figure1–1 Fewaspectsofourphysicalenvironmentinfluence our daily lives more than the weather.
Tornadoes are intense and destructive local storms of short duration that cause an average of about 55
deaths each year. (Photo by Wave RF/Photolibrary)
Chapter 1 Introduction to the Atmosphere 5
(a) (b)
Figure 1–2 These examples remind us that people influence the atmosphere and its behavior.
(a) Motor vehicles are a significant contributor to air pollution. This traffic jam was in Kuala Lumpur,
Malaysia. (Photo by Ron Yue/Alamy) (b) Smoke bellows from a coal-fired electricity-generating plant in
New Delhi, India, in June 2008. (AP Photo/Gurindes Osan)
Maps similar to the one in Figure 1–3 are familiar to everyone who checks the weather report in the
morning newspaper or on a television station. In addition to showing predicted high temperatures for
the day, this map shows other basic weather information about cloud cover, precipi-tation, and fronts.
Suppose you were planning a vacation trip to an unfa- miliar place. You would probably want to know
what kind of weather to expect. Such information would help as you selected clothes to pack and could
influence decisions regarding activities you might engage in during your stay. Unfortunately, weather
forecasts that go beyond a few days are not very dependable. Thus, it would not be possible to get a
reliable weather report about the conditions you are likely to encounter during your vacation.
Instead, you might ask someone who is familiar with the area about what kind of weather to expect.
“Are
thunderstorms common?” “Does it get cold at night?” “Are the afternoons sunny?” What you are
seeking is information about the climate, the conditions that are typical for that
Students Sometimes Ask …
Does meteorology have anything to do with meteors?
Yes, there is a connection. Most people use the word meteor when referring to solid particles
(meteoroids) that enter Earth’s atmosphere from space and “burn up” due to friction (“shooting stars”).
The term meteorology was coined in 340 BC, when the Greek philosopher Aristotle wrote a book titled
Meteorlogica, which included explanations of atmospheric and astronomical phenomena. In Aristotle’s
day anything that fell from or was seen in the sky was called a meteor. Today we distinguish between
particles of ice or water in the atmosphere (called hydrometeors) and extraterrestrial objects called
meteoroids, or meteors.
6
The Atmosphere: An Introduction to Meteorology
30s 20s H
10s 40s
50s
–0s
50s
cannot predict the weather. Although the place may usually (climatically) be warm, sunny, and dry
during the time of your planned vacation, you may actually experience cool, over- cast, and rainy
weather. There is a well-known saying that summarizes this idea: “Climate is what you expect, but
weather is what you get.”
The nature of both weather and cli-mate is expressed in terms of the same basic elements—those
quantities or properties that are measured regu- larly. The most important are (1) the temperature of
the air, (2) the humid- ity of the air, (3) the type and amount of cloudiness, (4) the type and amount of
precipitation, (5) the pressure exert- ed by the air, and (6) the speed and direction of the wind. These
elements constitute the variables by which weather patterns and climate types are depicted. Although
you will study these elements separately at first, keep in mind that they are very much inter-
0s
L
0s 20s
H
20s 0s
10s
50s
60s
–10s
Rain T-storm Snow Ice
place. Another useful source of such information is the great variety of climate tables, maps, and graphs
that are available. For example, the map in Figure 1–4 shows the average per- centage of possible
sunshine in the United States for the month of November, and the graph in Figure 1–5 shows average
daily high and low temperatures for each month, as well as extremes, for New York City.
Such information could, no doubt, help as you planned your trip. But it is important to realize that
climate data –0s
30s
40s 10s 70sH
20s
40s
A typical newspaper weather map for a day in late December. The color bands show the high
temperatures forecast for the day.
Figure 1–3
30 40
50 60
70
80 90
30
30 40
30 40
50
60
90
80
70 60
Figure 1–4 Mean percentage of possible sunshine for November. Southern Arizona is clearly the
sunniest area. By contrast, parts of the Pacific Northwest receive a much smaller percentage of the
possible sunshine. Climate maps such as this one are based on many years of data.
30s
50s
80s
Mostly cloudy
40 Mostly sunny
Partly cloudy
60
related. A change in one of the elements often produces changes in the others.
Concept Check 1.1
1 Distinguish among meteorology, weather, and climate.
2 List the basic elements of weather and climate.
48
44
40
36
32 90 28
ger price tag.
Between 1980 and 2010 the United States experienced
99 weather-related disasters in which overall damages
Chapter 1 Introduction to the Atmosphere 7
by all other weather events combined. Moreover, although
severe storms and floods usually generate more attention, 110 droughts can be just as devastating and
carry an even bigRecord
daily
Av
dail
highs
erage
y highs
Average
dai
ly lows Record daily lows
100
24 20
and costs reached or exceeded $1 billion (Figure 1–7). The 80 combined costs of these events exceeded
$725 billion (nor-
70
malized to 2007 dollars)! During the decade 1999–2008, an average of 629 direct weather fatalities
occurred per year in the United States. During this span, the annual economic impacts of adverse
weather on the national highway system alone exceeded $40 billion, and weather-related air traffic
delays caused $4.2 billion in annual losses.
16 60
12 8 4 0
50
40
At appropriate places throughout this book, you will Two entire chapters (Chapter 10 and Chapter 11)
focus
This is a scene on a day in late April in southern Arizona’s Organ Pipe Cactus National Monument. (Photo
by Michael Collier)
Question 1 Write two brief statements about the locale in this image—one that relates to weather and
one that relates to climate.
30 have an opportunity to learn about atmospheric hazards.
–4
–8
–12 10 –16
–20
– 24 –28 –32
20
0 –10 –20
JFMAMJJASOND Month Figure 1–5 Graph showing daily temperature data for New York City. In addition to the average daily
maximum and minimum temperatures for each month, extremes are also shown. As this graph shows,
there can be significant departures from the average.
Atmospheric Hazards: Assault by the Elements
Natural hazards are a part of living on Earth. Every day they adversely affect literally millions of people
worldwide and are responsible for staggering damages. Some, such as earthquakes and volcanic
eruptions, are geological. Many others are related to the atmosphere.
Occurrences of severe weather are far more fascinating than ordinary weather phenomena. A
spectacular light- ning display generated by a severe thunderstorm can elicit both awe and fear ( Figure
1–6a). Of course, hurricanes and tornadoes attract a great deal of much-deserved attention. A single
tornado outbreak or hurricane can cause billions of dollars in property damage, much human suffering,
and many deaths.
Of course, other atmospheric hazards adversely affect us. Some are storm related, such as blizzards, hail,
and freezing rain. Others are not direct results of storms. Heat waves, cold waves, fog, wildfires, and
drought are impor-tant examples (Figure 1–6b). In some years the loss of human life due to excessive
heat or bitter cold exceeds that caused
Temperature ( ̊C)
Temperature ( ̊F)
8 The Atmosphere: An Introduction to Meteorology
(a)
(b)
Figure 1–6 (a) Many people have incorrect perceptions of weather dangers and are unaware of the
relative differences of weather threats to human life. For example, they are awed by
the threat of hurricanes and tornadoes and plan accordingly on how to respond (for example, “Tornado
Awareness Week” each spring) but fail to realize that lightning and winter storms can be greater threats.
(Photo by Mark Newman/Superstock) (b) During the summer, dry weather coupled with lightning and
strong winds contribute to wildfire danger. Millions of acres are burned each year, especially in the West.
The loss of anchoring vegetation sets the stage for accelerated erosion when heavy rains subsequently
occur. Near Boulder, Colorado, October 10, 2010. (AP Photo/ The Daily Camera, Paul Aiken)
The Nature
of Scientific Inquiry
As members of a modern society, we are constantly reminded of the benefits derived from science. But
what exactly is the nature of scientific inquiry? Developing an understanding of how science is done and
how scientists work is an impor-tant theme in this book. You will explore the difficulties of gathering data and some of the ingenious methods that have been developed to overcome these difficulties. You
will also
almost entirely on hazardous weather. In addition, a number of the book’s special-interest boxes are
devoted to a broad variety of severe and hazardous weather, including heat waves, winter storms,
floods, dust storms, drought, mudflows, and lightning.
Every day our planet experiences an incredible assault by the atmosphere, so it is important to develop
an aware- ness and understanding of these significant weather events.
Concept Check 1.2
1 List at least five storm-related atmospheric hazards.
2 What are three atmospheric hazards that are not directly storm related?
916 892
Chapter 1 Introduction to the Atmosphere 9 Hypothesis
Once facts have been gathered and principles have been formulated to describe a natural phenomenon,
investigators try to explain
2
1
1
1
1
9
7
4
2
768howorwhythingshappeninthemanner observed. They often do this by construct-
644ingatentative(oruntested)explanation, which is called a scientific hypothesis. It is
520bestifaninvestigatorcanformulatemore than one hypothesis to explain a given set of
46observations.Ifanindividualscientistisun- able to devise multiple hypotheses, others in the scientific
community will almost always develop alternative explanations. A spirited debate frequently ensues. As
a result, exten-sive research is conducted by proponents of opposing hypotheses, and the results are
made available to the wider scientific com-
32 28 14 00
munity in scientific journals.
Before a hypothesis can become an
accepted part of scientific knowledge, it must pass objective testing and analysis. If a hypothesis cannot
be tested, it is not scientifically useful, no matter how in-teresting it might seem. The verification process requires that predictions be made based on the hypothesis being considered and the predictions
be tested by being compared against objective observations
Year
Between 1980 and 2010 the United States experienced 99 weather-related disasters in which overall
damages and costs reached or exceeded $1 billion. This bar graph shows the number of events that
occurred each year and the damage amounts in billions of dollars (normalized to 2007 dollars). The total
losses for the
99 events exceeded $725 billion! For more about these extraordinary events see
www.ncdc.noaa.gov/oa/reports/billionz.html. (After NOAA)
Figure 1–7
see examples of how hypotheses are formulated and tested, as well as learn about the development of
some significant scientific theories.
All science is based on the assumption that the natu-ral world behaves in a consistent and predictable
manner that is comprehensible through careful, systematic study. The overall goal of science is to
discover the underly- ing patterns in nature and then to use this knowledge to make predictions about
what should or should not be expected, given certain facts or circumstances. For example, by
understanding the processes and condi-tions that produce certain cloud types, meteorologists are often
able to predict the approximate time and place of their formation.
The development of new scientific knowledge involves some basic logical processes that are universally
accepted. To determine what is occurring in the natural world, sci- entists collect scientific facts through
observation and measurement. The types of facts that are collected often seek to answer a well-defined
question about the natural world, such as “Why does fog frequently develop in this place?” or “What
causes rain to form in this cloud type?” Because some error is inevitable, the accuracy of a particu- lar
measurement or observation is always open to question. Nevertheless, these data are essential to
science and serve as a springboard for the development of scientific theories (Box 1–1).
of nature. Put another way, hypotheses must fit observa-tions other than those used to formulate them
in the first place. Hypotheses that fail rigorous testing are ultimately discarded. The history of science is
littered with discarded hypotheses. One of the best known is the Earth-centered model of the
universe—a proposal that was supported by the apparent daily motion of the Sun, Moon, and stars
around Earth.
Theory
When a hypothesis has survived extensive scrutiny and when competing ones have been eliminated, a
hypothesis may be elevated to the status of a scientific theory. In ev- eryday language we may say,
“That’s only a theory.” But a scientific theory is a well-tested and widely accepted view that the scientific
community agrees best explains certain observable facts. Some theories that are extensively documented and extremely well supported are comprehensive in
scope. An example from the Earth sciences is the theory of plate tec-tonics, which provides the
framework for understanding the origin of mountains, earthquakes, and volcanic activity. It also explains
the evolution of continents and ocean basins through time. As you will see in Chapter 14, this theory
also helps us understand some important aspects of climate change through long spans of geologic time.
1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
Number of events
Damage amounts in billions of dollars
10 The Atmosphere: An Introduction to Meteorology
Box 1–1 Monitoring Earth from Space
Scientific facts are gathered in many ways, including through laboratory experiments and field
observations and measurements. Satellites provide another very important source of data. Satellite
images give us perspectives that are difficult to gain from more traditional sources (Figure 1–A).
Moreover, the high-tech instruments aboard many satellites enable scientists to gather information
from remote regions where data are otherwise scarce.
The image in Figure 1–B is from NASA’s Tropical Rainfall Measuring Mission (TRMM). TRMM is a
research satellite designed to expand our understanding of Earth’s water (hydrologic) cycle and its role
in our climate system. By covering the region between
the latitudes 35° north and 35° south, it provides much-needed data on rainfall and the heat release
associated with rainfall. Many types of measurements and images are possible. Instruments aboard the
TRMM satellite have greatly expanded our ability to collect precipitation data. In addition to recording
data for land areas, this satellite provides extremely precise measurements of rainfall over the oceans
where conventional land-based instruments cannot see. This
is especially important because much of Earth’s rain falls in ocean-covered tropical areas, and a great
deal of the globe’s weather-producing energy comes from
heat exchanges involved in the rainfall process. Until the TRMM, information on
the intensity and amount of rainfall over the tropics was scanty. Such data are crucial to understanding
and predicting global climate change.
FIGURE 1–B This map of rainfall for December 7–13, 2004, in Malaysia was constructed using TRMM
data. Over 800 millimeters (32 inches) of rain fell along the east coast of the peninsula (darkest red area).
The extraordinary rains caused extensive flooding and triggered many mudflows. (NASA/TRMM image)
Scientific Methods The processes just described, in which scientists gather facts through observations and formulate
scientific hypotheses and theories, is called the scientific method. Contrary to popu- lar belief, the
scientific method is not a standard recipe that scientists apply in a routine manner to unravel the secrets
of our natural world. Rather, it is an endeavor that involves creativity and insight. Rutherford and
Ahlgren put it this
FIGURE 1–A Satellite image of a massive winter storm on February 1, 2011. During a winter marked by
several crippling storms, this one stands out. Heavy snow, ice, freezing rain, and frigid winds battered
nearly two-thirds of the contiguous United States. In this image, the storm measures about 2000
kilometers (1240 miles) across. Satellites allow us to monitor the development and movement of major
weather systems. (NASA)
Sumatra
7.9 200
Malaysia
15.7 23.6 31.5 Inches 400 600 800 mm
way: “Inventing hypotheses or theories to imagine how the world works and then figuring out how they
can be put to the test of reality is as creative as writing poetry, composing music, or designing
skyscrapers.”*
*F. James Rutherford and Andrew Ahlgren, Science for All Americans (New York: Oxford University Press,
1990), p. 7.
Singapore
There is not a fixed path that scientists always follow that leads unerringly to scientific knowledge.
Nevertheless, many scientific investigations involve the following steps: (1) A question is raised about
the natural world; (2) scientific data are collected that relate to the question (Figure 1–8); (3) questions
are posed that relate to the data, and one or more working hypotheses are developed that may answer
these questions; (4) observations and experiments are devel- oped to test the hypotheses; (5) the
hypotheses are accepted, modified, or rejected, based on extensive testing; (6) data and results are
shared with the scientific community for critical and further testing.
Other scientific discoveries may result from purely theoretical ideas that stand up to extensive
examination. Some researchers use high-speed computers to simulate what is happening in the “real”
world. These models are useful when dealing with natural processes that occur on very long time scales
or take place in extreme or inacces-sible locations. Still other scientific advancements have been made
when a totally unexpected happening occurred during an experiment. These serendipitous discoveries
are more than pure luck; as Louis Pasteur stated, “In the field of observation, chance favors only the
prepared mind.” Scientific knowledge is acquired through several ave- nues, so it might be best to describe the nature of
scientific
Chapter 1 Introduction to the Atmosphere 11 Students Sometimes Ask…
In class you compared a hypothesis to a theory. How is each one different from a scientific law?
A scientific law is a basic principle that describes a particular behavior of nature that is generally narrow
in scope and can be stated briefly—often as a simple mathematical equation. Because scientific laws
have been shown time and time again to be consistent with observations and measurements, they are
rarely discarded. Laws may, however, require modifications to fit new findings. For example, Newton’s
laws of motion are still useful
for everyday applications (NASA uses them to calculate satellite trajectories), but they do not work at
velocities approaching the speed of light. For these circumstances, they have been supplanted by
Einstein’s theory of relativity.
inquiry as the methods of science rather than the scientific method. In addition, it should always be
remembered that even the most compelling scientific theories are still simpli- fied explanations of the
natural world.
Concept Check 1.3
1 How is a scientific hypothesis different from a scientific
theory?
2 List the basic steps followed in many scientific investigations.
Figure 1–8 Gathering data and making careful observations
are a basic part of scientific inquiry. (a) This Automated Surface Observing System (ASOS) installation is
one of nearly 900 in use for data gathering as part of the U.S. primary surface observing network. (Photo
by Bobbé Christopherson) (b) These scientists are working with a sediment core recovered from the
ocean floor. Such cores often contain useful data about Earth’s climate history. (Photo by Science
Source/Photo Researchers, Inc.)
(a)
(b)
12 The Atmosphere: An Introduction to Meteorology Students Sometimes Ask…
Who provides all the data needed to prepare
a weather forecast?
Data from every part of the globe are needed to produce accurate weather forecasts. The World
Meteorological Organization (WMO) was established by the United Nations to coordinate scientific
activity related to weather and climate. It consists of 187 member states and territories, representing all parts of the globe. Its World Weather Watch provides up-to-the-minute standardized observations
through member-operated observation systems. This global system involves more than 15 satellites,
10,000 land- observation and 7300 ship stations, hundreds of automated data buoys, and thousands of
aircraft.
Earth’s Spheres
The images in Figure 1–9 are considered to be classics be- cause they let humanity see Earth differently
than ever be- fore. Figure 1–9a, known as “Earthrise,” was taken when the Apollo 8 astronauts orbited
the Moon for the first time in December 1968. As the spacecraft rounded the Moon, Earth appeared to
rise above the lunar surface. Figure 1–9b, referred to as “The Blue Marble,” is perhaps the most widely
reproduced image of Earth; it was taken in December 1972 by the crew of Apollo 17 during the last
manned lunar mis-sion. These early views profoundly altered our conceptual- izations of Earth and
remain powerful images decades after they were first viewed. Seen from space, Earth is breathtak- ing
in its beauty and startling in its solitude. The photos remind us that our home is, after all, a planet—
small, self- contained, and in some ways even fragile. Bill Anders, the
Apollo 8 astronaut who took the “Earthrise” photo, expressed it this way: “We came all this way to
explore the Moon, and the most important thing is that we discovered the Earth.”
As we look closely at our planet from space, it becomes apparent that Earth is much more than rock and
soil. In fact, the most conspicuous features in Figure 1–9a are not continents but swirling clouds
suspended above the sur- face of the vast global ocean. These features emphasize the importance of
water on our planet.
The closer view of Earth from space shown in Figure 1–9b helps us appreciate why the physical
environment is tradi-tionally divided into three major parts: the solid Earth, the water portion of our
planet, and Earth’s gaseous envelope.
It should be emphasized that our environment is highly integrated and is not dominated by rock, water,
or air alone. It is instead characterized by continuous interactions as air comes in contact with rock, rock
with water, and water with air. Moreover, the biosphere, the totality of life forms on our planet, extends
into each of the three physical realms and is an equally integral part of the planet.
The interactions among Earth’s four spheres are incal- culable. Figure 1–10 provides us with one easy-tovisualize
example. The shoreline is an obvious meeting place for rock, water, and air. In this scene, ocean
waves that were created by the drag of air moving across the water are breaking against the rocky shore.
The force of the water can be powerful, and the erosional work that is accomplished can be great.
On a human scale Earth is huge. Its surface area occu- pies 500,000,000 square kilometers (193 million
square miles). We divide this vast planet into four independent parts. Because each part loosely
occupies a shell around Earth, we call them spheres. The four spheres include the geosphere (solid
Earth), the atmosphere (gaseous envelope), the hydrosphere (water portion), and the biosphere (life). Figure 1–9 (a) View, called “Earthrise,” that greeted the Apollo 8 astronauts as their spacecraft emerged
from behind the Moon. (NASA) (b) Africa and Arabia are prominent in this classic image called “The Blue
Marble” taken from Apollo 17. The tan cloud-free zones over the land coincide with major desert
regions. The band of clouds across central Africa is associated with a much wetter climate that in places
sustains tropical rain forests. The dark blue of the oceans and the swirling cloud patterns remind us of
the importance of the oceans and the atmosphere. Antarctica, a continent covered by glacial ice, is
visible at the South Pole. (NASA)
(a) (b)
Figure 1–10 The shoreline is one obvious example of an interface—a common boundary where different
parts of a system interact. In this scene, ocean waves (hydrosphere) that were created by the force of
moving air (atmosphere) break against a rocky shore (geosphere). (Photo by Radius Images/
photolibrary.com)
It is important to remember that these spheres are not separated by well-defined boundaries; rather,
each sphere is intertwined with all of the others. In addition, each of Earth’s four major spheres can be
thought of as being com- posed of numerous interrelated parts.
The Geosphere
Beneath the atmosphere and the ocean is the solid Earth, or geosphere. The geosphere extends from
the surface to the center of the planet, a depth of about 6400 kilometers (nearly 4000 miles), making it
by far the largest of Earth’s four spheres.
Based on compositional differences, the geosphere is divided into three principal regions: the dense
inner sphere, called the core; the less dense mantle; and the crust, which is the light and very thin outer
skin of Earth.
Soil, the thin veneer of material at Earth’s surface that supports the growth of plants, may be thought of
as part of all four spheres. The solid portion is a mixture of weathered rock debris (geosphere) and
organic matter from decayed plant and animal life (biosphere). The decomposed and dis- integrated
rock debris is the product of weathering process-es that require air (atmosphere) and water
(hydrosphere). Air and water also occupy the open spaces between the solid particles.
The Atmosphere
Earth is surrounded by a life-giving gaseous envelope called the atmosphere (Figure 1–11). When we
watch a high-flying jet plane cross the sky, it seems that the atmosphere extends upward for a great
distance. However, when compared to the thickness (radius) of the solid Earth (about 6400 kilome -ters
[4000 miles]), the atmosphere is a very shallow layer. More than 99 percent of the atmosphere is within
30 kilome-ters (20 miles) of Earth’s surface. This thin blanket of air is nevertheless an integral part of
the planet. It not only pro- vides the air that we breathe but also acts to protect us from the dangerous
radiation emitted by the Sun. The energy exchanges that continually occur between the atmosphere and
Earth’s surface and between the atmosphere and space produce the effects we call weather. If, like the Moon, Earth had no atmosphere, our planet would not only be lifeless, but many of the processes and
interactions that make the surface such a dynamic place could not operate.
The Hydrosphere
Earth is sometimes called the blue planet. More than any-thing else, water makes Earth unique. The
hydrosphere is a dynamic mass that is continually on the move, evapo-rating from the oceans to the
atmosphere, precipitating to
Chapter 1 Introduction to the Atmosphere 13
14
The Atmosphere: An Introduction to Meteorology
160 140 120 100
80 60 40 20
Noctilucent clouds
Top of troposphere
Figure 1–11 This unique image of Earth’s atmosphere merging with the emptiness
of space resembles an abstract painting.
It was taken in June 2007 by a Space Shuttle crew member. The silvery streaks (called noctilucent clouds)
high in the blue area are at a height of about 80 kilometers (50 miles). Air pressure at this height is less
than one-thousandth of that at sea level.
The reddish zone in the lower portion of the image is the densest part of the atmosphere. It is here, in a
layer called the troposphere, that practically all weather phenomena occur. Ninety percent of Earth’s
atmosphere occurs within just 16 kilometers (10 miles) of the surface. (NASA)
(2.5 miles) and in boiling hot springs. Moreover, air currents can carry microorganisms many kilometers
into the atmo- sphere. But even when we consider these extremes, life still must be thought of as being
confined to a narrow band very near Earth’s surface.
Plants and animals depend on the physical environ- ment for the basics of life. However, organisms do
more than just respond to their physical environment. Through
Earth’s surface
the land, and running back to the ocean again. The global ocean is certainly the most prominent feature
of the hydro-sphere, blanketing nearly 71 percent of Earth’s surface to an average depth of about 3800
meters (12,500 feet). It accounts for about 97 percent of Earth’s water (Figure 1–12). How- ever, the hydrosphere also includes the fresh water found in clouds, streams, lakes, and glaciers, as we ll as that
found underground.
Although these latter sources consti-tute just a tiny fraction of the total, they are much more important
than their meager percentage indicates. Clouds, of course, play a vital role in many weath- er and
climate processes. In addition to providing the fresh water that is so vital to life on land, streams,
glaciers, and groundwater are responsible for sculpt- ing and creating many of our planet’s varied
landforms.
The Biosphere
The biosphere includes all life on Earth (Figure 1–13). Ocean life is concentrated in the sunlit surface
waters of the sea. Most life on land is also concentrated near the surface, with tree roots and burrowing
animals reaching a few me-ters underground and flying insects and birds reaching a kilometer or so
above the surface. A surprising variety of life forms are also adapted to extreme en- vironments. For
example, on the ocean floor, where pressures are extreme and no light penetrates, there are places
where vents spew hot, mineral-rich fluids that support communities of ex- otic life-forms. On land, some
bacteria thrive in rocks as deep as 4 kilometers
Oceans 97.2%
Hydrosphere
2.8%
Glaciers 2.15%
Freshwater lakes 0.009% Saline lakes and inland seas 0.008%
Soil moisture 0.005% Atmosphere 0.001% Stream channels 0.0001%
Groundwater 0.62%
Stream channel
Glaciers
Groundwater (spring)
Nonocean Component (% of total hydrosphere)
Figure1–12 DistributionofEarth’swater.Obviously,mostofEarth’swaterisintheoceans. Glacial ice
represents about 85 percent of all the water outside the oceans. When only liquid freshwater is
considered, more than 90 percent is groundwater. (Glacier photo by Bernhard Edmaier/Photo
Researchers, Inc.; stream photo by E.J. Tarbuck; and groundwater photo by Michael Collier)
Altitude in kilometers (km)
Chapter 1 Introduction to the Atmosphere 15 (a)
countless interactions, life forms help maintain and alter their physical environment. Without life, the
makeup and nature of the geosphere, hydrosphere, and atmosphere would be very different.
Concept Check 1.4
 1 Compare the height of the atmosphere to the
 thickness of the geosphere.
 2 How much of Earth’s surface do oceans cover?
 3 How much of the planet’s total water supply do the oceans represent?
 4 List and briefly define the four spheres that constitute our environment.
Earth as a System
Anyone who studies Earth soon learns that our planet is a dynamic body with many separate but highly
interactive parts, or spheres. The atmo-sphere, hydrosphere, biosphere, and geosphere and all of their
components can be studied sepa-rately. However, the parts are not isolated. Each is related in many
ways to the others, producing a complex and continuously interacting whole that we call the Earth
system.
Earth System Science
A simple example of the interactions among dif-ferent parts of the Earth system occurs every winter as
moisture evaporates from the Pacific Ocean and subsequently falls as rain in the hills of southern
California, triggering destructive de- bris flows (Figure 1–14). The processes that move water from the
hydrosphere to the atmosphere and then to the geosphere have a profound impact on the physical
environment and on the plants and animals (including humans) that inhabit the affected regions.
Scientists have recognized that in order to more fully understand our planet, they must learn how its
individual components (land, water, air, and life-forms) are interconnected. This endeavor, called Earth
system science, aims to
study Earth as a system composed of numerous interacting parts, or subsystems. Using an
interdisciplinary approach, those who practice Earth system science attempt to achieve the level of
understanding necessary to comprehend and solve many of our global environmental problems.
A system is a group of interacting, or interdependent, parts that form a complex whole. Most of us hear
and use the term system frequently. We may service our car’s cooling system, make use of the city’s
transportation system,
(b) Figure 1–13 (a) The ocean contains a significant portion
of Earth’s biosphere. Modern coral reefs are unique and complex examples and are home to about 25
percent of all marine species. Because of this diversity, they are sometimes referred to as the ocean
equivalent of tropical rain forests. (Photo by Darryl Leniuk/agefotostock) (b) Tropical rain forests are
characterized by hundreds of different species per square kilometer. Climate has a strong influence on
the nature of the biosphere. Life, in turn, influences the atmosphere. (Photo by
agefotostock/SuperStock)
16 The Atmosphere: An Introduction to Meteorology
Figure 1–14 This image provides an example of interactions among different parts of the Earth system.
On January 10, 2005, extraordinary rains triggered this debris flow (popularly called a mudslide) in the
coastal community of La Conchita, California. (AP Wideworld Photo)
and be a participant in the political system. A news report might inform us of an approaching weather
system. Further, we know that Earth is just a small part of a largersystem known as the solar system,
which in turn is a subsystem of an even larger system called the Milky Way Galaxy.
The Earth System
The Earth system has a nearly endless array of subsystems in which matter is recycled over and over
again. One example that is described in Box 1–2 traces the movements of carbon among Earth’s four
spheres. It shows us, for example, that
the carbon dioxide in the air and the carbon in living things and in certain rocks is all part of a subsystem
described by the carbon cycle.
The parts of the Earth system are linked so that a change in one part can produce changes in any or all of
the other parts. For example, when a volcano erupts, lava from Earth’s interior may flow out at the
surface and block a nearby valley. This new obstruction influences the region’s drainage system by
creating a lake or causing streams to change course. The large quantities of volcanic ash and gases that
can be emitted during an eruption might be blown high into the atmosphere and influence the amount
of solar energy that can reach Earth’s surface. The result could be a drop in air temperatures over the
entire hemisphere.
Where the surface is covered by lava flows or a thick layer of volcanic ash, existing soils are buried. This
causes the soil-forming processes to begin anew to transform the new surface material into soil ( Figure
1–15). The soil that eventually forms will reflect the interactions among many parts of the Earth
system—the volcanic parent material, the climate, and the impact of biological activity. Of course, there
would also be significant changes in the biosphere. Some organisms and their habitats would be
eliminated by the lava and ash, whereas new settings for life, such as the lake, would be created. The
potential climate change could also impact sensitive life-forms.
The Earth system is characterized by processes that vary on spatial scales from fractions of mil limeters
to thousands of kilometers. Time scales for Earth’s processes range from milliseconds to billions of years. As we learn about Earth, it becomes increasingly clear that despite significant separa-tions in distance
or time, many processes are connected, and a change in one component can influence the entire system.
The Earth system is powered by energy from two sourc- es. The Sun drives external processes that occur
in the atmo-sphere, hydrosphere, and at Earth’s surface. Weather and climate, ocean circulation, and
erosional processes are driv- en by energy from the Sun. Earth’s interior is the second source of energy.
Heat remaining from when our planet formed and heat that is continuously generated by radioac-tive
decay power the internal processes that produce volca- noes, earthquakes, and mountains.
Humans are part of the Earth system, a system in which the living and nonliving components are
entwined and interconnected. Therefore, our actions produce changes in all the other parts. When we
burn gasoline and coal, dispose of our wastes, and clear the land, we cause other parts of the system to
respond, often in unforeseen ways. Throughout this book you will learn about some of Earth’s
subsystems, including the hydrologic system and the climate system. Remember that these components
and we humans are all part of the complex interacting whole we call the Earth system.
Concept Check 1.5
1 What is a system? List three examples.
2 What are the two sources of energy for the Earth system?
Figure 1–15 When Mount St. Helens erupted in May 1980, the area shown here was buried by a volcanic
mudflow. Now, plants are reestablished and new soil is forming. (Photo by Terry Donnelly/ Alamy)
Composition of the Atmosphere
Introduction to the Atmosphere ATMOSPHERE ▸Composition of the Atmosphere
In the days of Aristotle, air was thought to be one of four fundamental substances that could not be
further divided into constituent components. The other three substances were fire, earth (soil), and
water. Even today the term air is sometimes used as if it were a specific gas, which of course it is not.
The envelope of air that surrounds our planet is a mixture of many discrete gases, each with its own
physical properties, in which varying quantities of tiny solid and liq- uid particles are suspended.
Major Components
The composition of air is not constant; it varies from time to time and from place to place (see Box 1–3).
If the water vapor, dust, and other variable components were removed
from the atmosphere, we would find that its makeup is very stable up to an altitude of about 80
kilometers (50 miles).
As you can see in Figure 1–16, two gases—nitrogen and oxygen—make up 99 percent of the volume of
clean, dry air. Although these gases are the most plentiful components of the atmosphere and are of
great significance to life on Earth, they are of little or no importance in affecting weather phenomena. The remaining 1 percent of dry air is mostly the inert gas argon (0.93 percent) plus tiny quantities of a
number of other gases.
Carbon Dioxide
Carbon dioxide, although present in only minute amounts (0.0391 percent, or 391 parts per million), is
nevertheless a meteorologically important constituent of air. Carbon dioxide is of great interest to
meteorologists because it is an efficient absorber of energy emitted by Earth and thus influences the
heating of the atmosphere. Although the proportion of carbon dioxide in the atmosphere is relatively
Chapter 1 Introduction to the Atmosphere 17
18 The Atmosphere: An Introduction to Meteorology
Box 1–2 The Carbon Cycle: One of Earth’s Subsystems
To illustrate the movement of material and energy in the Earth system, let us take a brief look at the
carbon cycle (Figure 1–C). Pure carbon is relatively rare in nature. It
is found predominantly in two minerals: diamond and graphite. Most carbon is bonded chemically to
other elements to
form compounds such as carbon dioxide, calcium carbonate, and the hydrocarbons found in coal and
petroleum. Carbon is also the basic building block of life as it readily combines with hydrogen and
oxygen to form the fundamental organic compounds that compose living things.
In the atmosphere, carbon is found mainly as carbon dioxide (CO2). Atmospheric carbon dioxide is
significant because it is a greenhouse gas, which means it is an efficient absorber of energy emitted by
Earth and thus influences the heating of the atmosphere. Because
many of the processes that operate on
Earth involve carbon dioxide, this gas
is constantly moving into and out of the atmosphere. For example, through the process of
photosynthesis, plants absorb carbon dioxide from the atmosphere to produce the essential organic
compounds needed for growth. Animals that consume these plants (or consume other animals that eat
plants) use these organic compounds as a source of energy and, through the process
FIGURE 1–C Simplified diagram of the carbon cycle, with emphasis on the flow of carbon between the
atmosphere and the hydrosphere, geosphere, and biosphere. The colored arrows show whether the
flow of carbon is into or out of the atmosphere.
Burning and decay of biomass
Photosynthesis by vegetation
Burial of biomass
Photosynthesis and respiration of marine organisms Deposition of carbonate sediments
CO2 dissolves in seawater
Weathering of carbonate rock
Volcanic activity
Weathering of granite
Respiration by land organisms
Burning of fossil fuels
Lithosphere
Sediment and sedimentary rock
CO2 entering the atmosphere
CO2 leaving the atmosphere
Carbon dioxide (0.0391% or 391 ppm)
Nitrogen (78.084%)
1.5 Krypton (Kr) 1.14
of respiration, return carbon dioxide to the atmosphere. (Plants also return some CO2 to the
atmosphere via respiration.) Further,
when plants die and decay or are burned, this biomass is oxidized, and carbon dioxide is returned to the
atmosphere.
Methane (CH4)
Concentration in parts per million (ppm)
uniform, its percentage has been rising steadily for more than a century. Figure 1–17 is a graph showing
the growth in atmospheric CO2 since 1958. Much of this rise is attributed to the burning of everincreasing
quantities of fossil fuels, such as coal and oil. Some of this additional carbon dioxide is
absorbed by the waters of the ocean or is used by plants, but more than 40 percent remains in the air.
Estimates pro- ject that by sometime in the second half of the twenty- first century, carbon dioxide
levels will be twice as high as pre-industrial levels.
Most atmospheric scientists agree that increased carbon dioxide concentrations have contributed to a
warming of Earth’s atmosphere over the past several decades and will continue to do so in the decades
to come. The magnitude of such temperature changes is uncertain and depends partly on the quantities of CO2 contributed by human activities in the years ahead. The role of carbon dioxide in the atmosphere
and its possible effects on climate are examined in more detail in Chapters 2 and 14.
Argon (0.934%)
All others
Oxygen (20.946%)
18.2
Neon (Ne)
Helium (He) 5.24
Hydrogen (H ) 0.5 2
Figure 1–16 Proportional volume of gases composing dry air. Nitrogen and oxygen obviously dominate.
Chapter 1 Introduction to the Atmosphere 19
Not all dead plant material decays immediately back to carbon dioxide. A small percentage is deposited
as sediment. Over long spans of geologic time, considerable biomass is buried with sediment. Under the
right conditions, some of these carbon-rich deposits are converted to fossil fuels—coal, petroleum, or
natural gas. Eventually some
of the fuels are recovered (mined or pumped from a well) and burned to run factories and fuel our
transportation system. One result of fossil-fuel combustion is the release of huge quantities of CO2 into
the atmosphere. Certainly one of the most active parts of the carbon cycle is the movement of CO2 from
the atmosphere to the biosphere and back again.
Carbon also moves from the geosphere and hydrosphere to the atmosphere and back again. For
example, volcanic activity early in Earth’s history is thought to be
the source of much of the carbon dioxide found in the atmosphere. One way that carbon dioxide makes
its way back to the hydrosphere and then to the solid Earth
is by first combining with water to form carbonic acid (H2CO3), which then attacks the rocks that
compose the geosphere. One product of this chemical weathering
of solid rock is the soluble bicarbonate
ion (2HCO3–), which is carried by groundwater and streams to the ocean. Here water-dwelling
organisms extract this dissolved material to produce hard parts (shells) of calcium carbonate (CaCO3).
When the organisms die, these skeletal
remains settle to the ocean floor as biochemical sediment and become sedimentary rock. In fact, the
geosphere is by far Earth’s largest depository of carbon, where it is a constituent of a variety of rocks,
the most abundant being limestone (Figure 1–D). Eventually the limestone
may be exposed at Earth’s surface, where chemical weathering will cause the carbon stored in the rock
to be released to the atmosphere as CO2. 390 380 370 360 350 340 330 320
In summary, carbon moves among all four of Earth’s major spheres. It is essential to every living thing in
the biosphere. In the atmosphere carbon dioxide is an important greenhouse gas. In the hydrosphere,
carbon dioxide is dissolved in lakes, rivers, and the ocean. In the geosphere, carbon is contained in
carbonate-rich sediments and sedimentary rocks and is stored as organic matter dispersed through
sedimentary rocks and as deposits of coal and petroleum.
FIGURE 1–D
A great deal of carbon is
locked up in Earth’s geosphere.
England’s White Chalk Cliffs are an example.
Chalk is a soft, porous type of limestone (CaCO3) consisting mainly of the hard parts of microscopic
organisms called coccoliths (inset). (Photo by Prisma/SuperStock; inset by Steve Gschmeissner/Photo
Researchers, Inc.)
Variable Components
Air includes many gases and particles that vary significantly from time to time and place to place.
Important examples include water vapor, aerosols, and ozone. Although usually present in small
percentages, they can have significant ef- fects on weather and climate.
Water Vapor The amount of water vapor in the air var- ies considerably, from practically none at all up
to about 4 percent by volume. Why is such a small fraction of the
Figure 1–17 Changes in the atmosphere’s carbon dioxide (CO2) as measured at Hawaii’s Mauna Loa
Observatory. The oscillations reflect the seasonal variations in plant growth and decay in the Northern
Hemisphere. During the first 10 years of this record (1958–1967), the average yearly CO2 increase was
0.81 ppm. During the last 10 years (2001–2010) the average yearly increase was 2.04 ppm. (Data from
NOAA)
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
CO2 concentration (ppm)
20 The Atmosphere: An Introduction to Meteorology
Box 1–3 Origin and Evolution of Earth’s Atmosphere
The air we breathe is a stable mixture of 78 percent nitrogen, 21 percent oxygen, nearly 1 percent argon,
and small amounts of gases such as carbon dioxide and water vapor. However, our planet’s original
atmosphere 4.6 billion years ago was substantially different. Earth’s Primitive Atmosphere
Early in Earth’s formation, its atmosphere likely consisted of gases most common in the early solar
system: hydrogen, helium, methane, ammonia, carbon dioxide, and water vapor. The lightest of these
gases, hydrogen and helium, escaped into space because Earth’s gravity was too weak to hold them.
Most of the remaining gases were probably scattered into space by strong solar winds (vast streams of
particles) from a young active Sun. (All stars, including the Sun, apparently experience a highly active
stage early in their evolution, during which solar winds are very intense.)
Earth’s first enduring atmosphere was generated by a process called outgassing, through which gases
trapped in the planet’s interior are released. Outgassing from hundreds of active volcanoes still remains
an important planetary function worldwide (Figure 1–E). However, early in Earth’s history, when
massive heating and fluid-like motion occurred in the planet’s interior, the
gas output must have been immense. Based on our understanding of modern volcanic eruptions, Earth’s
primitive atmosphere probably consisted of mostly water vapor,
carbon dioxide, and sulfur dioxide, with minor amounts of other gases and minimal nitrogen. Most
importantly, free oxygen was not present.
atmosphere so significant? The fact that water vapor is the source of all clouds and precipitation would
be enough to ex- plain its importance. However, water vapor has other roles. Like carbon dioxide, it has
the ability to absorb heat given off by Earth, as well as some solar energy. It is therefore impor-tant
when we examine the heating of the atmosphere.
When water changes from one state to another, such as from a gas to a liquid or a liquid to a solid (see
Figure 4–3,
Students Sometimes Ask…
Could you explain a little more about why the graph in
Figure 1–17 has so many ups and downs?
Sure. Carbon dioxide is removed from the air by photosynthesis, the process by which green plants
convert sunlight into chemical energy. In spring and summer, vigorous plant growth in the extensive
land areas of the Northern Hemisphere removes carbon dioxide from the atmosphere, so the graph
takes a dip. As winter approaches, many plants die or shed leaves. The decay of organic matter returns
carbon dioxide to the air, causing the graph to spike upward.
p. 99), it absorbs or releases heat. This energy is termed latent heat, which means hidden heat. As you
will see in later chapters, water vapor in the atmosphere transports this latent heat from one region to
another, and it is the energy source that drives many storms.
Aerosols The movements of the atmosphere are sufficient to keep a large quantity of solid and liquid
particles sus- pended within it. Although visible dust sometimes clouds the sky, these relatively large particles are too heavy to stay in the air very long. Still, many particles are microscopic and remain
suspended for considerable periods of time. They may originate from many sources, both natural and
human made, and include sea salts from breaking waves, fine soil blown into the air, smoke and soot
from fires, pollen and mi- croorganisms lifted by the wind, ash and dust from volcanic eruptions, and
more (Figure 1–18a). Collectively, these tiny solid and liquid particles are called aerosols.
Aerosols are most numerous in the lower atmosphere near their primary source, Earth’s surface.
Nevertheless, the upper atmosphere is not free of them, because some dust is
FIGURE 1–E Earth’s first enduring atmosphere was formed by a process called outgassing, which
continues today, from hundreds of active volcanoes worldwide. (Photo by Greg Vaughn/Alamy)
Oxygen in the Atmosphere
As Earth cooled, water vapor condensed
to form clouds, and torrential rains began
to fill low-lying areas, which became the oceans. In those oceans, nearly 3.5 billion years ago,
photosynthesizing bacteria began to release oxygen into the water. During photosynthesis, organisms
use the Sun’s energy to produce organic material (energetic molecules of sugar containing hydrogen and
carbon) from carbon dioxide (CO2) and water (H2O). The first bacteria probably used hydrogen sulfide
(H2S) as the source of hydrogen rather than water. One of the earliest bacteria, cyanobacteria (once
called blue-green algae), began to produce oxygen as a by-product of photosynthesis.
Initially, the newly released oxygen was readily consumed by chemical reactions with other atoms and
molecules (particularly iron) in the ocean (Figure 1–F). Once the available iron satisfied its need for
oxygen and as the number of oxygen-generating organisms increased, oxygen began to build in the
atmosphere. Chemical analyses of rocks suggest that a significant amount
of oxygen appeared in the atmosphere as early as 2.2 billion years ago and increased steadily until it
reached stable levels about 1.5 billion years ago. Obviously, the availability of free oxygen had a major
impact on the development of life and vice versa. Earth’s atmosphere evolved together with its lifeforms
from an oxygen-free envelope to an oxygen-rich environment.
FIGURE 1–F These ancient layered, iron-rich rocks, called banded iron formations, were deposited during
a geologic span known as the Precambrian. Much of the oxygen generated as a by-product of
photosynthesis was readily consumed by chemical reactions with iron to produce these rocks. (Photo by
John Cancalosi/Photolibrary)
Chapter 1 Introduction to the Atmosphere 21
carried to great heights by rising currents of air, and other particles are contributed by meteoroids that
disintegrate as they pass through the atmosphere.
From a meteorological standpoint, these tiny, often invisible particles can be significant. First, many act
as sur- faces on which water vapor may condense, an important function in the formation of clouds and fog. Second, aero-sols can absorb or reflect incoming solar radiation. Thus, when an air-pollution
episode is occurring or when ash fills the sky following a volcanic eruption, the amount of sun- light
reaching Earth’s surface can be measurably reduced. Finally, aerosols contribute to an optical
phenomenon we have all observed—the varied hues of red and orange at sunrise and sunset (Figure 1–
18b).
Ozone Another important component of the atmosphere is ozone. It is a form of oxygen that combines
three oxygen atoms into each molecule (O3). Ozone is not the same as the oxygen we breathe, which
has two atoms per molecule (O2). There is very little ozone in the atmosphere. Overall, it rep-resents
just 3 out of every 10 million molecules. Moreover,
its distribution is not uniform. In the lowest portion of the atmosphere, ozone represents less than 1
part in 100 million. It is concentrated well above the surface in a layer called the stratosphere, between
10 and 50 kilometers (6 and 31 miles).
In this altitude range, oxygen molecules (O2) are split into single atoms of oxygen (O) when they absorb
ultraviolet radiation emitted by the Sun. Ozone is then created when a single atom of oxygen (O) and a
molecule of oxygen (O2) collide. This must happen in the presence of a third, neu-tral molecule that
acts as a catalyst by allowing the reaction to take place without itself being consumed in the process.
Ozone is concentrated in the 10- to 50-kilometer height range because a crucial balance exists there:
The ultraviolet radia-tion from the Sun is sufficient to produce single atoms of oxygen, and there are
enough gas molecules to bring about the required collisions.
The presence of the ozone layer in our atmosphere is crucial to those of us who are land dwellers. The
reason is that ozone absorbs the potentially harmful ultraviolet (UV) radiation from the Sun. If ozone did
not filter a great deal of the ultraviolet radiation, and if the Sun’s UV rays reached
Another significant benefit of the “oxygen explosion” is that oxygen molecules (O2) readily absorb
ultraviolet radiation and rearrange themselves to form ozone (O3). Today, ozone is concentrated above
the surface in a layer called the stratosphere, where it absorbs much of the ultraviolet radiation that
strikes the upper atmosphere.
For the first time, Earth’s surface was protected from this type of solar radiation, which is particularly
harmful to DNA. Marine organisms had always been shielded from ultraviolet radiation by
the oceans, but the development of the atmosphere’s protective ozone layer made the continents
more hospitable.
22
The Atmosphere: An Introduction to Meteorology
(a)
(b)
Dust storm Air pollution
(a) This satellite image from November 11, 2002, shows two examples of aerosols. First, a large dust
storm is blowing across northeastern China toward the Korean Peninsula. Second, a dense haze toward
the south (bottom center) is human-generated air pollution. (b) Dust in the air can cause sunsets to be
especially colorful. (Satellite image courtesy of NASA; photo by elwynn/ Shutterstock)
Figure 1–18
the surface of Earth undiminished, land areas on our planet would be uninhabitable for most life as we
know it. Thus, anything that reduces the amount of ozone in the atmo-sphere could affect the wellbeing
of life on Earth. Just such a problem is described in the next section.
Concept Check 1.6
 1 Is air a specific gas? Explain.
 2 What are the two major components of clean, dry air? What proportion does each represent?
 3 Why are water vapor and aerosols important constituents of Earth’s atmosphere?
 4 What is ozone? Why is ozone important to life on Earth?
Ozone Depletion—
A Global Issue
The loss of ozone high in the atmosphere as a consequence of human activities is a serious global-scale
environmental problem. For nearly a billion years Earth’s ozone layer has
protected life on the planet. However, over the past half cen-tury, people have unintentionally placed
the ozone layer in jeopardy by polluting the atmosphere. The most significant of the offending chemicals
are known as chlorofluorocarbons (CFCs). They are versatile compounds that are chemically stable,
odorless, nontoxic, noncorrosive, and inexpensive to produce. Over several decades many uses were
developed for CFCs, including as coolants for air-conditioning and refrigeration equipment, as cleaning
solvents for electronic components, as propellants for aerosol sprays, and in the production of certain
plastic foams.
Students Sometimes Ask…
Isn’t ozone some sort of pollutant?
Yes, you’re right. Although the naturally occurring ozone in the stratosphere is critical to life on Earth, it
is regarded as a pollutant when produced at ground level because it can damage vegetation and be
harmful to human health. Ozone is a major component
in a noxious mixture of gases and particles called photochemical smog. It forms as a result of reactions
triggered by sunlight that occur among pollutants emitted by motor vehicles and industries. Chapter 13
provides more information about this. No one worried about how CFCs might affect the atmo-sphere until three scientists, Paul Crutzen, F.
Sherwood Rowland, and Mario Molina, studied the relationship. In 1974 they alerted the world when
they reported that CFCs were probably reducing the average concentration of ozone in the stratosphere.
In 1995 these scientists were awarded the Nobel Prize in chemistry for their pioneering work.
They discovered that because CFCs are practically inert (that is, not chemically active) in the lower
atmosphere, a portion of these gases gradually makes its way to the ozone layer, where sunlight
separates the chemicals into their constituent atoms. The chlorine atoms released this way, through a
complicated series of reactions, have the net effect of removing some of the ozone.
The Antarctic Ozone Hole
Although ozone depletion by CFCs occurs worldwide, mea-surements have shown that ozone
concentrations take an especially sharp drop over Antarctica during the Southern Hemisphere spring
(September and October). Later, during November and December, the ozone concentration recovers to
more normal levels (Figure 1–19). Between 1980, when it was discovered, and the early 2000s, this wellpublicized
ozone hole intensified and grew larger until it covered an area roughly the size of North
America (Figure 1–20).
The hole is caused in part by the relatively abundant ice particles in the south polar stratosphere. The ice
boosts the effectiveness of CFCs in destroying ozone, thus caus- ing a greater decline than would
otherwise occur. The zone
of maximum depletion is confined to the Antarctic region by a swirling upper-level wind pattern. When
this vortex weakens during the late spring, the ozone-depleted air is no longer restricted and mixes
freely with air from other lati-tudes where ozone levels are higher.
A few years after the Antarctic ozone hole was discov- ered, scientists detected a similar but smaller
ozone thin- ning in the vicinity of the North Pole during spring and early summer. When this pool breaks
up, parcels of ozone- depleted air move southward over North America, Europe, and Asia.
Effects of Ozone Depletion
Because ozone filters out most of the damaging UV radia-tion in sunlight, a decrease in its
concentration permits more of these harmful wavelengths to reach Earth’s surface. What are the effects
of the increased ultraviolet radiation? Each 1 percent decrease in the concentration of stratospheric
ozone increases the amount of UV radiation that reaches Earth’s surface by about 2 percent. Therefore,
because ul-traviolet radiation is known to induce skin cancer, ozone depletion seriously affects human
health, especially among fair-skinned people and those who spend considerable time in the sun.
The fact that up to a half million cases of these cancers occur in the United States annually means that
ozone deple-tion could ultimately lead to many thousands more cases each year.* In addition to raising
the risk of skin cancer, an increase in damaging UV radiation can negatively impact the human immune
system, as well as promote cataracts, a clouding of the eye lens that reduces vision and may cause
blindness if not treated. The effects of additional UV radiation on animal and plant life are also important. There is serious
concern that crop yields and quality will be adversely affected. Some scientists also fear that increased
UV radiation in the Ant- arctic will penetrate the waters surrounding the continent and impair or destroy
the microscopic plants, called phy-toplankton, that represent the base of the food chain. A decrease in
phytoplankton, in turn, could reduce the popu- lation of copepods and krill that sustain fish, whales,
pen- guins, and other marine life in the high latitudes of the Southern Hemisphere.
Montreal Protocol
What has been done to protect the atmosphere’s ozone layer? Realizing that the risks of not curbing
CFC emissions were difficult to ignore, an international agreement known as the Montreal Protocol on
Substances That Deplete the Ozone Layer was concluded under the auspices of the United Nations in
late 1987. The protocol established legally binding controls
* For more on this, see Severe and Hazardous Weather: “The Ultraviolet Index,” p. 49.
Chapter 1 Introduction to the Atmosphere 23
30
25
20
15
10
5
Area of North
America
Extent of 2006
ozone hole
Extent 2010 ozone
h
of ole
Aug Sep
Oct Nov Dec
Figure 1-19 Changes in the size of the Antarctic ozone hole during 2006 and 2010. The ozone hole in
both years began
to form in August and was well developed in September and October. As is typical, each year the ozone hole persisted through November and disappeared in December. At its maximum, the area of the ozone
hole was about 22 million square kilometers in 2010, an area nearly as large as all of North America.
Million square kilometers
24 The Atmosphere: An Introduction to Meteorology
Area of North Americ
Extent
Area of Antarctica
ozone hole
of
1979
Ozone (Dobson Units) 110 220 330 440 550
30 25a 20
15
10
5
1980 1985 1990 1995 2000 2005 2010 2015
2010 Year
The two satellite images show ozone distribution in the Southern Hemisphere on the days in September
1979 and 2010 when the ozone hole was largest. The dark blue shades over Antarctica correspond to
the region with the sparsest ozone. The ozone hole is not technically a “hole” where no ozone is present
but is actually a region of exceptionally depteted ozone in
the stratosphere over the Antarctic that occurs in the spring. The small graph traces changes in the
maximum size of the ozone hole, 1980–2010. (NOAA)
Figure 1–20
on the production and consumption of gases known to cause ozone depletion. As the scientific
understanding of ozone depletion improved after 1987 and substitutes and alternatives became
available for the offending chemicals, the Montreal Protocol was strengthened several times. More than
190 nations eventually ratified the treaty.
The Montreal Protocol represents a positive international response to a global environment problem. As
a result of the action, the total abundance of ozone-depleting gases in the atmosphere has started to decrease in recent years. Accord- ing to the U.S. Environmental Protection Agency (U.S. EPA), the ozone
layer has not grown thinner since 1998 over most of the world.* If the nations of the world continue to
follow the provisions of the protocol, the decreases are expected to continue throughout the twenty –
first century. Some offend- ing chemicals are still increasing but will begin to decrease in coming
decades. Between 2060 and 2075, the abundance of ozone-depleting gases is projected to fall to values
that exist- ed before the Antarctic ozone hole began to form in the 1980s.
Concept Check 1.7
 1 What are CFCs, and what is their connection to the ozone
 problem?
 2 During what time of year is the Antarctic ozone hole well developed?
 3 Describe three effects of ozone depletion.
 4 What is the Montreal Protocol?
* U.S. EPA, Achievements in Stratospheric Ozone Protection, Progress Report. EPA-430-R-07-001, April
2007, p. 5.
Vertical Structure of the Atmosphere
ATMOSPHERE
Introduction to the Atmosphere
▸Extent of the Atmosphere/Thermal Structure of the Atmosphere
To say that the atmosphere begins at Earth’s surface and ex-tends upward is obvious. However, where
does the atmo-sphere end and where does outer space begin? There is no sharp boundary; the
atmosphere rapidly thins as you travel away from Earth, until there are too few gas molecules to detect.
Pressure Changes
To understand the vertical extent of the atmosphere, let us examine the changes in atmospheric
pressure with height. Atmospheric pressure is simply the weight of the air above. At sea level the
average pressure is slightly more than 1000 millibars. This corresponds to a weight of slightly more than
1 kilogram per square centimeter (14.7 pounds per square inch). Obviously, the pressure at higher
altitudes is less (Figure 1–21).
One-half of the atmosphere lies below an altitude of 5.6 kilometers (3.5 miles). At about 16 kilometers
(10 miles), 90 percent of the atmosphere has been traversed, and above 100 kilometers (62 miles) only
0.00003 percent of all the gases composing the atmosphere remain.
At an altitude of 100 kilometers the atmosphere is so thin that the density of air is less than could be
found in the most perfect artificial vacuum at the surface. Nevertheless, the atmosphere continues to
even greater heights. The truly Million square kilometers
Chapter 1 Introduction to the Atmosphere 25
Kathy Orr, Broadcast Meteorologist
KATHY ORR is an award-winning broadcast meteorologist in Philadelphia. (Photo courtesy of Kathy Orr)
not the ‘rip and read’ of years gone by. We take data from the supercomputers in Wash- ington or
models by the Navy and make our own forecasts. There are some services that provide forecasts locally
and nationally, but they’re not located where we are. I can look out the window and tell whether those
fore- casts are going to be accurate or not.”
As a weathercaster, Orr has worked to promote education in science and math. For three years, she led
a community program called Kidcasters. By offering children a chance to present the weather on TV, Orr
hoped to interest elementary school children in science and math. For the past nine sum- mers, she has
conducted a similar program called Orr at the Shore. Each program highlights environmental issues
along the New Jersey coast.
My job is to explain complicated ideas to people in an uncomplicated way.
Orr continues to promote science literacy by volunteering for the American Meteoro- logical Society’s
DataStreme Atmosphere Project. As a DataStreme mentor, she has vis- ited dozens of schools to train
teachers in the science of meteorology. The teachers then promote the use of weather lessons in their
districts to pique student interest in science, mathematics, and technology. Orr considers her forecasts
educational as well. “My job is to explain complicated ideas to people in an uncomplicated way.”
Being a weathercaster, Orr says, is demanding but also exhilarating. “In TV,
the hours are crazy. If you work mornings, you’re up at 2 AM; if nights, you’re up until midnight. So you
really have to love it. But if you do, you’ll find a way. And I feel blessed to have done this for so long.”
Kathy Orr is a trusted and familiar face
on the airwaves of Philadelphia. As chief meteorologist for CBS3, Orr has kept the City of Brotherly Love
abreast of the weather for 18 years and earned 10 regional Emmy awards in the process.
Orr calls being a television weathercaster a dream come true.
Orr calls being a television weather- caster a dream come true. Growing up in Syracuse, New York, Orr
operated her own miniature weather station and marveled at the snow squalls that howled across Lake
Ontario. “It could be a sunny afternoon, then the wind would blow over the lake. All of
a sudden there was a blinding blizzard,” she says.
When not watching the skies, Orr stayed glued to her family’s TV set. At the time, she couldn’t see how to combine her two major interests. “There weren’t any women doing the weather on
television back then. There were also not a lot of meteorologists on TV; it was less about the science and
more for comic relief,” she says.
She majored in broadcasting at Syracuse University and went on to earn a second degree in
meteorology at the State University of New York at Oswego. There she learned the basis for the snow
squalls that transfixed her as a girl. “These kinds of phenomena are associated with being on the
downwind side of a Great Lake. When wind comes along, the lake acts like a snowmaking machine.”
While still in school, Orr landed a job as
the weathercaster on a Syracuse station’s brand-new morning show. She’s remained a television
meteorologist ever since.
Today, Orr says, being a trained meteorol- ogist “is definitely a competitive advantage. It’s
rarefied nature of the outer atmosphere is described very well by Richard Craig:
The earth’s outermost atmosphere, the part above a few hundred kilometers, is a region of extremely
low density. Near sea level, the number of atoms and molecules in a cubic centimeter of air is about 2 3
1019; near 600 km, it is only about 2 3 107, which is the sea-level value divided by a million million. At
sea level, an atom or molecule can be expected, on the average, to move about 7 3 1026 cm before
colliding with another particle; at the 600-km level, this distance, called the “mean free path,” is about
10 km. Near
sea level, an atom or molecule, on the average, undergoes about 7 3 109 such collisions each second;
near 600 km, this number is reduced to about 1 each minute.*
The graphic portrayal of pressure data (Figure 1–21) shows that the rate of pressure decrease is not
constant. Rather, pressure decreases at a decreasing rate with an increase in altitude until, beyond an
altitude of about 35 kilometers (22 miles), the decrease is negligible.
*Richard Craig, The Edge of Space: Exploring the Upper Atmosphere (New York: Doubleday & Company,
Inc., 1968), p. 130.
26
The Atmosphere: An Introduction to Meteorology
36 32 28 24 20 16 12
8 4
lies below
22 20 18 16 14 12 10 8 6 4 2
Cap t. Kittinger, USAF
1961 31. (102,800
Air press
Air pressure at top of Mt. Evere
(29,035 ft) is
314 m
b
3 km ft)
ure = 9.6
st
atm this
50% of
osphere altitude
mb
200
400
Pressure (mb)
1000
This jet is cruising at an altitude of 10 kilometers (6.2 miles). (Photo by inter- light/Shutterstock)
Question 1 Refer to the graph in Figure 1–21. What is the approximate air pressure where the jet is
flying?
Question 2 About what percentage of the atmosphere is below the jet (assuming that the pressure at
the surface is 1000 millibars)?
Although measurements had not been taken above a height of about 10 kilometers (6 miles), scientists
believed that the temperature continued to decline with height to a value of absolute zero (–273°C) at
the outer edge of the atmo-sphere. In 1902, however, the French scientist Leon Philippe Teisserenc de
Bort refuted the notion that temperature Figure 1–22 Temperatures drop with an increase in altitude in the troposphere. Therefore, it is possible
to have snow on a mountaintop and warmer, snow-free lowlands below. (Photo by David Wall/Alamy)
600 800
Figure 1–21 Atmospheric pressure changes with altitude.
The rate of pressure decrease with an increase in altitude is not constant. Rather, pressure decreases
rapidly near Earth’s surface and more gradually at greater heights.
Put another way, data illustrate that air is highly compressible—that is, it expands with decreasing
pressure and becomes compressed with increasing pressure. Conse- quently, traces of our atmosphere
extend for thousands of kilometers beyond Earth’s surface. Thus, to say where the atmosphere ends
and outer space begins is arbitrary and, to a large extent, depends on what phenomenon one is study –
ing. It is apparent that there is no sharp boundary.
In summary, data on vertical pressure changes show that the vast bulk of the gases making up the
atmosphere is very near Earth’s surface and that the gases gradually merge with the emptiness of space.
When compared with the size of the solid Earth, the envelope of air surrounding our planet is indeed
very shallow.
Temperature Changes
By the early twentieth century much had been learned about the lower atmosphere. The upper
atmosphere was partly known from indirect methods. Data from balloons and kites had revealed that
the air temperature dropped with increas- ing height above Earth’s surface. This phenomenon is felt by
anyone who has climbed a high mountain and is obvious in pictures of snow-capped mountaintops rising
above snow- free lowlands (Figure 1–22).
Altitude (km)
Altitude (miles)
decreases continuously with an increase in altitude. In studying the results of more than 200 balloon
launchings, Teisserenc de Bort found that the temperature stopped decreas- ing and leveled off at an
altitude between 8 and 12 kilometers (5 and 7.5 miles). This sur- prising discovery was at first doubted,
but subsequent data-gathering confirmed his findings. Later, through the use of balloons and rocketsounding
techniques, the temper- ature structure of the atmosphere up to great heights became clear.
Today the atmosphere is divided vertically into four layers on the basis of temperature (Figure 1–23).
Troposphere The bottom layer in which we live, where temperature decreases with an increase in
altitude, is the troposphere. The term was coined in 1908 by Teisserrenc de Bort and literally means the
region where air “turns over,” a reference to the apprecia- ble vertical mixing of air in this lowermost
zone.
140 130 120 110 100 90 80 70 60 50 40 30 20 10
Aurora
Meteor
THERMOSPHERE
Mesopause
MESOSPHERE
Stratopause
STRATOSPHERE
Tropopause
TROPOSPHERE
10 20 30 30
90
80
70
60
50
40
30
20
10
50 ̊C
Chapter 1 Introduction to the Atmosphere
27
Maximum ozone
The temperature decrease in the troposphere
is called the environmental lapse
rate. Its average value is 6.5°C per kilome-ter (3.5°F per 1000 feet), a figure known as
the normal lapse rate. It should be emphasized,
however, that the environmental
lapse rate is not a constant but rather can be
highly variable and must be regularly measured.
To determine the actual environmental
lapse rate as well as gather information
about vertical changes in air pressure, wind,
and humidity, radiosondes are used. A radiosonde is an instrument package that is attached to a
balloon and trans- mits data by radio as it ascends through the atmosphere (Figure 1–24). The
environmental lapse rate can vary dur- ing the course of a day with fluctuations of the weather, as well
as seasonally and from place to place. Sometimes shallow layers where temperatures actually increase
with height are observed in the troposphere. When such a rever-sal occurs, a temperature inversion is
said to exist.*
The temperature decrease continues to an average height of about 12 kilometers (7.5 miles). Yet the
thick- ness of the troposphere is not the same everywhere. It reaches heights in excess of 16 kilometers
(10 miles) in the tropics, but in polar regions it is more subdued, extend- ing to 9 kilometers (5.5 miles)
or less (Figure 1–25). Warm surface temperatures and highly developed thermal mix- ing are responsible
for the greater vertical extent of the tro- posphere near the equator. As a result, the environmental
lapse rate extends to great heights; and despite relatively high surface temperatures below, the lowest
tropospheric temperatures are found aloft in the tropics and not at the poles.
*Temperature inversions are described in greater detail in Chapter 13.
Mt. Everest
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10
–140 –120 –100 –80 –60 –40 –20 0 20 40 60 80 100 120 ̊F 32
Temperature
Figure 1–23 Thermal structure of the atmosphere.
The troposphere is the chief focus of meteorologists because it is in this layer that essentially all
important weather phenomena occur. Almost all clouds and certainly all precipitation, as well as all our
violent storms, are born in this lowermost layer of the atmosphere. This is why the troposphere is often
called the “weather sphere.”
Stratosphere Beyond the troposphere lies the stratosphere; the boundary between the troposphere
and the stratosphere is known as the tropopause. Below the tropopause, atmospheric properties are
readily transferred by large-scale turbulence and mixing, but above it, in the stratosphere, they are not. In the stratosphere, the tempera-ture at first remains nearly constant to a height of about 20 kilometers
(12 miles) before it begins a sharp increase that continues until the stratopause is encountered at a
height of about 50 kilometers (30 miles) above Earth’s surface. Higher temperatures occur in the
stratosphere because it is in this layer that the atmosphere’s ozone is concentrated. Recall that ozone
absorbs ultraviolet radiation from the Sun. Con-sequently, the stratosphere is heated by the Sun.
Although the maximum ozone concentration exists between 15 and 30 kilometers (9 and 19 miles), the
smaller amounts of ozone above this height range absorb enough UV energy to cause the higher
observed temperatures.
Height (km)
Height (miles)
Temperature
28 The Atmosphere: An Introduction to Meteorology
Pole
Tropopause
Tropical tropopause
Middle latitude
tropopause
Polar tropopause
Equator
30 27 24 21 18 15 12
9 6 3 0
–70 –60 –50 –40 –30 –20 –10 Temperature ( ̊C)
0 10 20
Figure 1–24 A lightweight instrument package, the radiosonde, is suspended below a 2-meter-wide
weather balloon. As
the radiosonde is carried aloft, sensors measure pressure, temperature, and relative humidity. A radio
transmitter sends the measurements to a ground receiver. By tracking the radiosonde
in flight, information on wind speed and direction aloft is also obtained. Observations where winds aloft
are obtained are called “rawinsonde” observations. Worldwide, there are about 900 upper-air
observation stations. Through international agreements, data are exchanged among countries. (Photo
by Mark Burnett/ Photo Researchers, Inc.) Mesosphere In the third layer, the mesosphere, temper- atures again decrease with height until at the
mesopause, some 80 kilometers (50 miles) above the surface, the aver- age temperature approaches
290°C (2130°F). The coldest temperatures anywhere in the atmosphere occur at the me-sopause. The
pressure at the base of the mesosphere is only about one-thousandth that at sea level. At the
mesopause, the atmospheric pressure drops to just one-millionth that at sea level. Because accessibility
is difficult, the mesosphere is one of the least explored regions of the atmosphere. The reason is that it
cannot be reached by the highest-flying airplanes and research balloons, nor is it accessible to the
Figure 1–25 Differences in the height of the tropopause. The variation in the height of the tropopause,
as shown on the small inset diagram, is greatly exaggerated.
lowest-orbiting satellites. Recent technical developments are just beginning to fill this knowledge gap.
Thermosphere The fourth layer extends outward from the mesopause and has no well-defined upper
limit. It is the thermosphere, a layer that contains only a tiny frac- tion of the atmosphere’s mass. In the
extremely rarified air of this outermost layer, temperatures again increase, due to the absorption of very
shortwave, high-energy solar radia-tion by atoms of oxygen and nitrogen.
Temperatures rise to extremely high values of more than 1000°C (1800°F) in the thermosphere. But such
temperatures are not comparable to those experienced near Earth’s sur- face. Temperature is defined in
terms of the average speed at which molecules move. Because the gases of the thermo-sphere are
moving at very high speeds, the temperature is very high. But the gases are so sparse that collectively
they possess only an insignificant quantity of heat. For this reason, the temperature of a satellite
orbiting Earth in the thermosphere is determined chiefly by the amount of solar
Altitude (km)
Chapter 1 Introduction to the Atmosphere 29
radiation it absorbs and not by the high temperature of the almost nonexistent surrounding air. If an
astronaut inside were to expose his or her hand, the air in this layer would not feel hot.
Concept Check 1.8
 1 Does air pressure increase or decrease with an increase in
 altitude? Is the rate of change constant or variable? Explain.
 2 Is the outer edge of the atmosphere clearly defined? Explain.
 3 The atmosphere is divided vertically into four layers on the basis of temperature. List these
layers in order from lowest to highest. In which layer does practically all of our weather occur?
 4 Why does temperature increase in the stratosphere?
 5 Why are temperatures in the thermosphere not strictly
 comparable to those experienced near Earth’s surface? Vertical Variations in Composition
In addition to the layers defined by vertical variations in temperature, other layers, or zones, are also
recognized in the atmosphere. Based on composition, the atmosphere is often divided into two layers:
the homosphere and the heterosphere. From Earth’s surface to an altitude of about 80 kilometers (50
miles), the makeup of the air is uniform in terms of the proportions of its component gases. That is, the
composition is the same as that shown earlier, in Figure 1–16. This lower uniform layer is termed the
homosphere, the zone of homogeneous composition.
In contrast, the very thin atmosphere above 80 kilometers is not uniform. Because it has a
heterogeneous composition, the term heterosphere is used. Here the gases are arranged into four
roughly spherical shells, each with a distinctive composition. The lowermost layer is dominated by
molec- ular nitrogen (N2), next, a layer of atomic oxygen (O) is encountered, followed by a layer
dominated by helium (He) atoms, and finally a region consisting largely of hydrogen (H) atoms. The
stratified nature of the gases making up the heterosphere varies according to their weights. Molecular
nitrogen is the heaviest, and so it is lowest. The lightest gas, hydrogen, is outermost.
Ionosphere
Located in the altitude range between 80 to 400 kilometers (50 to 250 miles), and thus coinciding with
the lower portions of the thermosphere and heterosphere, is an electrically charged layer known as the
ionosphere. Here molecules of nitrogen and atoms of oxygen are readily ionized as they
When this weather balloon was launched, the surface temperature was 17°C. It is now at an altitude of 1
kilometer. (Photo by David R. Frazier/ Photo Researchers, Inc.)
Question 1 What term is applied to the instrument package being car-ried aloft by the balloon?
Question 2 In what layer of the atmosphere is the balloon? Question 3 If average conditions prevail,
what air temperature is the
instrument package recording? How did you figure this out?
Question 4 How will the size of the balloon change, if at all, as it rises through the atmosphere? Explain.
absorb high-energy shortwave solar energy. In this process, each affected molecule or atom loses one or
more electrons and becomes a positively charged ion, and the electrons are set free to travel as electric
currents.
Although ionization occurs at heights as great as 1000 kilometers (620 miles) and extends as low as
perhaps 50 kilometers (30 miles), positively charged ions and nega-tive electrons are most dense in the
range of 80 to 400 kilo- meters (50 to 250 miles). The concentration of ions is not great below this zone
because much of the short-wavelength radiation needed for ionization has already been depleted.
30 The Atmosphere: An Introduction to Meteorology In addition, the atmospheric density at this level results in a large percentage of free electrons being
swiftly cap-tured by positively charged ions. Beyond the 400-kilometer (250-mile) upward limit of the
ionosphere, the concentra-tion of ions is low because of the extremely low density of the air. Because
so few molecules and atoms are present, relatively few ions and free electrons can be produced.
The electrical structure of the ionosphere is not uni- form. It consists of three layers of varying ion
density. From bottom to top, these layers are called the D, E, and F lay- ers, respectively. Because the
production of ions requires direct solar radiation, the concentration of charged parti- cles changes from
day to night, particularly in the D and E zones. That is, these layers weaken and disappear at night and
reappear during the day. The uppermost layer, or F layer, on the other hand, is present both day and
night. The density of the atmosphere in this layer is very low, and positive ions and electrons do not
meet and recombine as rapidly as they do at lesser heights, where density is higher. Consequently, the
concentration of ions and electrons in the F layer does not change rapidly, and the layer, although weak,
remains through the night.
The Auroras
As best we can tell, the ionosphere has little impact on our daily weather. But this layer of the
atmosphere is the site of one of nature’s most interesting spectacles, the auroras (Figure 1–26). The
aurora borealis (northern lights) and
its Southern Hemisphere counterpart, the aurora australis (southern lights), appear in a wide variety of
forms. Some-times the displays consist of vertical streamers in which there can be considerable
movement. At other times the auroras appear as a series of luminous expanding arcs or as a quiet glow
that has an almost foglike quality.
The occurrence of auroral displays is closely correlated in time with solar-flare activity and, in geographic
location, with Earth’s magnetic poles. Solar flares are massive mag- netic storms on the Sun that emit
enormous amounts of energy and great quantities of fast-moving atomic particles. As the clouds of
protons and electrons from the solar storm approach Earth, they are captured by its magnetic field,
which in turn guides them toward the magnetic poles. Then, as the ions impinge on the ionosphere,
they energize the atoms of oxygen and molecules of nitrogen and cause them to emit light—the glow of
the auroras. Because the occur-rence of solar flares is closely correlated with sunspot activ- ity, auroral
displays increase conspicuously at times when sunspots are most numerous.
Concept Check 1.9
1 Distinguish between the homosphere and the heterosphere. 2 What is the ionosphere? Where in the
atmosphere is it located? 3 What is the primary cause of the auroras?
Figure 1–26 Aurora borealis (northern lights) as seen from Alaska. The same phenomenon occurs
toward the South Pole, where it is called the aurora australis (southern lights). (Photo by agefotostock/
SuperStock)
Give It Some Thought 1. Determine which statements refer to weather and which refer to climate. (Note: One
statement includes aspects of both weather and climate.)
2. a. The baseball game was rained out today.
a. January is Omaha’s coldest month.
b. North Africa is a desert.
c. The high this afternoon was 25°C.
d. Last evening a tornado ripped through central Oklahoma.
e. I am moving to southern Arizona because it is warm and sunny.
f. Thursday’s low of –20°C is the coldest temperature ever recorded for that city.
g. It is partly cloudy.
3. After entering a dark room, you turn on a wall switch,
4. but the light does not come on. Suggest at least three hypotheses that might explain this
observation.
5. Making accurate measurements and observations is
a basic part of scientific inquiry. The accompanying radar image, showing the distribution and
intensity
of precipitation associated with a storm, provides
one example. Identify three additional images in this chapter that illustrate ways in which
scientific data are gathered. Suggest advantages that might be associated with each example.
greenhouse gases have increased global average
temperatures.
b. One or two studies suggest that hurricance intensity is increasing.
5. Refer to Figure 1–21 to answer the following questions.
6. If you were to climb to the top of Mount Everest,
7. how many breaths of air would you have to take at
8. that altitude to equal one breath at sea level?
9. If you are flying in a commercial jet at an altitude of 12 kilometers, about what
percentage of the atmosphere’s mass is below you?
6. If you were ascending from the surface of Earth to the top of the atmosphere, which one of the
following would be most useful for determining the layer of the atmosphere you were in? Explain.
a. Doppler radar

  1. click here for more information on this paper

b. Hygrometer (humidity)
c. Weather satellited. Barometer (air pressure)
e. Thermometer (temperature)
7. The accompanying photo provides an example of interactions among different parts of the Earth
system. It is a view of a mudflow that was triggered by extraordinary rains. Which of Earth’s four
“spheres” were involved in this natural disaster that buried a small town on the Philippine island of
Leyte? Describe how each contributed to the mudflow.
(Photo by AP Photo/Pat Roque)
8. Where would you expect the thickness of the troposphere (that is, the distance between Earth’s
surface and the tropopause) to be greater: over Hawaii or Alaska? Why? Do you think it is likely that the
thickness of the troposphere over Alaska is different in January than in July? If so, why?
Chapter 1 Introduction to the Atmosphere 31
(Image by National Weather Service)
4. During a conversation with your meteorology professor, she makes the two statements listed below.
Which can be considered a hypothesis? Which is more likely a theory?
a. After several decades, the science community has determined that human-generated
32 The Atmosphere: An Introduction to Meteorology
INTRODUCTION TO THE ATMOSPHERE IN REVIEW
 ● Meteorology is the scientific study of the atmosphere. Weather refers to the state of the
atmosphere at a given time and place. It is constantly changing, sometimes from hour to hour
and other times from day to day. Climate is an aggregate
 of weather conditions, the sum of all statistical weather information that helps describe a place
or region. The
nature of both weather and climate is expressed in terms
of the same basic elements, those quantities or properties measured regularly. The most
important elements are (1) air temperature, (2) humidity, (3) type and amount of cloudiness, (4)
type and amount of precipitation, (5) air pressure, and
 (6) the speed and direction of the wind.
 ● All science is based on the assumption that the natural world
 behaves in a consistent and predictable manner. The process by which scientists gather facts
through observation and careful measurement and formulate scientific hypotheses and theories
is often referred to as the scientific method.  ● Earth’s four spheres include the atmosphere (gaseous envelope), the geosphere (solid Earth),
the hydrosphere (water portion),
and the biosphere (life). Each sphere is composed of many interrelated parts and is intertwined
with all the other spheres.
 ● Although each of Earth’s four spheres can be studied separately, they are all related in a
complex and continuously interacting whole that we call the Earth system. Earth system science
uses an interdisciplinary approach to integrate the knowledge of several academic fields in the
study of our planet and its global environmental problems.
 ● A system is a group of interacting parts that form a complex whole. The two sources of energy
that power the Earth system are (1) the Sun, which drives the external processes that occur in
the atmosphere, hydrosphere, and at Earth’s surface, and (2) heat from Earth’s interior that
powers the internal processes that produce volcanoes, earthquakes, and mountains.
 ● Air is a mixture of many discrete gases, and its composition varies from time to time and
place to place. After water vapor, dust, and other variable components are removed, two gases,
nitrogen and oxygen, make up 99 percent of the volume of the remaining clean, dry air. Carbon
dioxide, although present
 in only minute amounts (0.0391 percent, or 391 ppm), is an efficient absorber of energy emitted
by Earth and thus influences the heating of the atmosphere.
 ● The variable components of air include water vapor, dust particles, and ozone. Like carbon
dioxide, water vapor can absorb heat given off by Earth as well as some solar energy. When
water vapor changes from one state to another, it absorbs or releases heat. In the atmosphere,
water vapor transports this latent (“hidden”) heat from one place
 to another, and it is the energy source that helps drive
many storms. Aerosols (tiny solid and liquid particles) are meteorologically important because
these often-invisible particles act as surfaces on which water can condense and are also
absorbers and reflectors of incoming solar radiation. Ozone, a form of oxygen that combines
three oxygen atoms into each molecule (O3), is a gas concentrated in the 10- to 50-kilometer
height range in the atmosphere that absorbs the potentially harmful ultraviolet (UV) radiation
from the Sun.
● Over the past half century, people have placed Earth’s
ozone layer in jeopardy by polluting the atmosphere with chlorofluorocarbons (CFCs), which remove
some of the gas. Ozone concentrations take an especially sharp drop over Antarctica duri ng the
Southern Hemisphere spring (September and October). Ozone depletion seriously affects human health,
especially among fair-skinned people and those who spend considerable time in the Sun. The Montreal
Protocol, concluded under the auspices of the United Nations, represents a positive international
response to the ozone problem. ● No sharp boundary to the upper atmosphere exists. The atmosphere simply thins as you travel away
from Earth, until there are too few gas molecules to detect. Traces of atmosphere extend for thousands
of kilometers beyond Earth’s surface.
● Using temperature as the basis, the atmosphere is divided into four layers. The temperature decrease
in the troposphere, the bottom layer in which we live, is called the environmental lapse rate. Its average
value is 6.5°C per kilometer, a figure known
as the normal lapse rate. The environmental lapse rate is not a constant and must be regularly
measured using radiosondes. The thickness of the troposphere is generally greater in the tropics than in
polar regions. Essentially all important weather phenomena occur in the troposphere. Beyond the
troposphere lies the stratosphere; the boundary between the troposphere and stratosphere is known as
the tropopause. In the stratosphere, the temperature at first remains constant to a height of about 20
kilometers (12 miles) before it begins a sharp increase due to the absorption of ultraviolet radiation
from the Sun by ozone. The temperatures continue to increase until the stratopause is encountered at a
height of about 50 kilometers (30 miles). In the mesosphere, the third layer, temperatures again
decrease with height until the mesopause, some 80 kilometers (50 miles) above the surface. The fourth
layer, the thermosphere, with no well-defined upper limit, consists of extremely rarefied air.
Temperatures here increase with an increase in altitude.
● The atmosphere is often divided into two layers, based
on composition. The homosphere (zone of homogeneous composition), from Earth’s surface to an
altitude of about
80 kilometers (50 miles), consists of air that is uniform in terms of the proportions of its component
gases. Above 80 kilometers, the heterosphere (zone of heterogenous composition) consists of gases
arranged into four roughly spherical shells, each with a distinctive composition. The stratified nature of
the gases in the heterosphere varies according to their weights.
● Occurring in the altitude range between 80 and 400 kilometers (50 and 250 miles) is an electri cally
charged layer known as the ionosphere. Here molecules of nitrogen and atoms of oxygen are readily
ionized as they absorb high-energy, shortwave solar energy. Three layers of varying ion density make up
the ionosphere. Auroras (the aurora borealis, northern lights, and its Southern Hemisphere counterpart
the aurora australis, southern lights) occur within the ionosphere. Auroras form as clouds of protons
and electrons ejected from the Sun during solar-flare activity enter the atmosphere near Earth’s
magnetic poles and energize the atoms of oxygen and molecules of nitrogen, causing them to emit
light—the glow of the auroras.
aerosols (p. 21)
air (p. 17)
atmosphere (p. 13) aurora australis (p. 29) aurora borealis (p. 29) biosphere (p. 15) climate (p. 5)
elements of weather and climate (p. 7) environmental lapse rate (p. 26) geosphere (p. 13)
hydrosphere (p. 14)
hypothesis (p. 9)
ionosphere (p. 29) mesopause (p. 27) mesosphere (p. 27) meteorology (p. 4) ozone (p. 21)
PROBLEMS
radiosonde (p. 26) stratopause (p. 27) stratosphere (p. 27) system (p. 16) theory (p. 10) thermosphere (p.
27) tropopause (p. 27) troposphere (p. 26) weather (p. 5)
VOCABULARY REVIEW
8. a.
On a spring day a middle-latitude city (about 40°N latitude) has a surface (sea-level) temperature of 10°C.
If vertical soundings reveal a nearly constant environmental lapse rate of 6.5°C per kilometer and a
temperature
at the tropopause of –55°C, what is the height of the tropopause?
Chapter 1 Introduction to the Atmosphere 33
10. Refer to the newspaper-type weather map in Figure 1–3 to answer the following:
a. Estimate the predicted high temperatures in central New York State and the
northwest corner of Arizona.
b. Where is the coldest area on the weather map? Where is the warmest?
c. On this weather map, H stands for the center of a region of high pressure. Does it
appear as though high pressure is associated with precipitation or fair weather?
d. Which is warmer—central Texas or central Maine? Would you normally expect this to
be the case?
11. Refer to the graph in Figure 1–5 to answer the following questions about temperatures in New
York City:
a. What is the approximate average daily high temperature in January? In July?
b. Approximately what are the highest and lowest temperatures ever recorded?
12. Refer to the graph in Figure 1–7. Which year had the greatest number of billion-dollar weather
disasters? How many events occurred that year? In which year was the damage amount
greatest?
13. Refer to the graph in Figure 1–21 to answer the following:
a. Approximately how much does the air pressure drop (in
b. millibars) between the surface and 4 kilometers? (Use a
c. surface pressure of 1000 millibars.)
d. How much does the pressure drop between 4 and 8 e. kilometers?
f. Based on your answers to parts a and b, answer the
g. following: With an increase in altitude, air pressure decreases at a(n) (constant,
increasing, decreasing) rate. Underline the correct answer.
5. If the temperature at sea level were 23°C, what would the air temperature be at a height of 2
kilometers, under average conditions?
6. Use the graph of the atmosphere’s thermal structure (Figure 1–23) to answer the following:
14. What are the approximate height and temperature of the stratopause?
15. At what altitude is the temperature lowest? What is the temperature at that height?
7. Answer the following questions by examining the graph in Figure 1–25:
16. In which one of the three regions (tropics, middle latitudes, poles) is the surface temperature
lowest?
17. In which region is the tropopause encountered at the lowest altitude? The highest? What are
the altitudes and temperatures of the tropopause in those regions?
b. On the same spring day a station near the equator
has a surface temperature of 25°C, 15°C higher than
the middle-latitude city mentioned in part a. Vertical soundings reveal an environmental lapse rate of
6.5°C per kilometer and indicate that the tropopause is encountered at 16 kilometers. What is the air
temperature at the tropopause?
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version of this book to enhance your study of Introduction to the Atmosphere.Heating Earth’s Surface and Atmosphere
From our everyday experiences, we know that the Sun’s rays feel warmer and paved roads become
much hotter on clear, sunny days compared to overcast days. Pictures of snowcapped mountains
remind us that temperatures decrease with altitude. And we know that the fury of winter is always
replaced by the newness of spring. What you may not know is that these are manifestations of the same
phenomenon that causes the blue color of the sky and the red color of a brilliant sunset. All these are a
result of the interaction of solar radiation with Earth’s atmosphere and its land–sea surface.
This power plant in Andalucia, Spain, produces clean thermoelectric power from the Sun. (Photo by
Kevin Foy/Alamy)
After completing this chapter, you should be able to:
 Explain what causes the Sun angle and length of daylight to change during the year and
describe how these changes produce the seasons.
 Calculate the noon Sun angle for any latitude on the equinoxes and the solstices.
 Define temperature and explain how it is different from the total kinetic energy contained in a
substance.
 Contrast the concepts of latent heat and sensible heat.
 List and describe the three mechanisms of heat transfer.
Sketch and label a diagram that shows the fate of incoming solar radiation.
Explain what causes blue skies and red sunsets. Explain what is meant by the statement “The
atmosphere is heated from the ground up.”
Describe the role of water vapor and carbon dioxide in producing the greenhouse effect.
Sketch and label a diagram illustrating Earth’s heat budget.
35
36 The Atmosphere: An Introduction to Meteorology Earth–Sun Relationships
Heating Earth’s Surface and Atmosphere ATMOSPHERE ▸Understanding Seasons
The amount of solar energy received at any location varies with latitude, time of day, and season of the
year. Contrasting images of polar bears and perpetual ice and palm trees along a tropical beach serve to
illustrate the extremes (Figure 2–1). The unequal heating of Earth’s land–sea surface creates
winds and drives the ocean’s currents, which in turn trans- port heat from the tropics toward the poles
in an unending attempt to balance energy inequalities.
The consequences of these processes are the phenomena we call weather. If the Sun were “turned off,”
global winds and ocean currents would quickly cease. Yet as long as the Sun shines, winds will blow and weather will persist. So to understand how the dynamic weather machine works, we must know why
different latitudes receive different quan-tities of solar energy and why the amount of solar energy
received changes during the course of a year to produce the seasons.
Earth’s Motions
Earth has two principal motions—rotation and revolution. Rotation is the spinning of Earth on its axis
that produces the daily cycle of day and night.
The other motion, revolution, refers to Earth’s move- ment in a slightly elliptical orbit around the Sun.
The dis-tance between Earth and Sun averages about 150 million kilometers (93 million miles). Because
Earth’s orbit is not perfectly circular, however, the distance varies during the course of a year. Each year,
on about January 3, our planet is about 147.3 million kilometers (91.5 million miles) from the Sun, closer
than at any other time—a position called perihe- lion. About six months later, on July 4, Earth is about
152.1 million kilometers (94.5 million miles) from the Sun, farther away than at any other time—a
position called aphelion. Although Earth is closest to the Sun and receives up to 7 percent more energy
in January than in July, this difference plays only a minor role in producing seasonal temperature
variations, as evidenced by the fact that Earth is closest to the Sun during the Northern Hemisphere
winter.
What Causes the Seasons?
If variations in the distance between the Sun and Earth do not cause seasonal temperature changes,
what does? The gradual but significant change in day length certainly accounts for some of the
difference we notice between summer and winter. Furthermore, a gradual change in the angle (altitude)
of the Sun above the horizon is also a major contributing fac-tor (Figure 2–2). For example, someone
living in Chicago, Illi-nois, experiences the noon Sun highest in the sky in late June. But as summer gives
way to autumn, the noon Sun appears lower in the sky, and sunset occurs earlier each evening.
The seasonal variation in the angle of the Sun above the horizon affects the amount of energy received
at Earth’s sur- face in two ways. First, when the Sun is directly overhead (at a 90° angle), the solar rays
are most concentrated and thus most intense. At lower Sun angles, the rays become more spread out
and less intense (Figure 2–3). You have probably experienced this when using a flashlight. If the beam
strikes a surface perpendicularly, a small intense spot is produced. By contrast, if the flashlight beam
strikes at any other angle, the area illuminated is larger—but noticeably dimmer.
Second, but of less significance, the angle of the Sun de-termines the path solar rays take as they pass
through the
(a)
(b)
Figure 2–1 An understanding of Earth-Sun relationships is
basic to an understanding of weather and climate. (a) In tropical latitudes, temperature contrasts during the year are modest. (Photo by Maria Skaldina/Shutterstock) (b) In polar regions, seasonal temperature
contrasts can be dramatic. (Photo by Michael Collier)
June 21-22
Longest day
March 21-22 September 22-23
ESun E angle
Day and night equal
73 1/2° NSNS
Chapter 2 Heating Earth’s Surface and Atmosphere 37
Sun angle 50°
(a) Summer solstice at 40°N latitude
(b) Spring or fall equinox at 40°N latitude
June 21-22
24 hours of daylight
December 21-22
Shortest day
WW
Noon Sun
EE Midnight
Sun
N 261/2° S N 331/2° S
WW
(c) Winter solstice at 40°N latitude (d) Summer solstice at 80°N latitude
Figure 2–2 Daily paths of the Sun for a place located at 40° north latitude for the (a) summer solstice; (b)
spring or fall equinox, and (c) winter solstice and for a place located at 80° north latitude at the (d)
summer solstice.
Sun angle
Sun angle atmosphere (Figure 2–4). When the Sun is directly overhead, the rays strike the atmosphere at a 90°
angle and travel the shortest possible route to the surface. This distance is re- ferred to as 1 atmosphere.
However, rays entering the atmos- phere at a 30° angle musttravel twice this distance before reaching
the surface, while rays at a 5° angle travel through
a distance roughly equal to the thickness of 11 atmospheres (Table 2–1). The longer the path, the
greater the chance that sunlight will be dispersed by the atmosphere, which re- duces the intensity at
the surface. These conditions account for the fact that we cannot look directly at the midday Sun but we
enjoy gazing at a sunset.
1 unit
1 unit
90 ̊
45 ̊
1.4 units
30 ̊
2 units
Figure 2–3 Changes in the Sun’s angle cause variations in the amount of solar energy reaching Earth’s
surface. The higher the angle, the more intense the solar radiation.
1 unit
1 unit
38
The Atmosphere: An Introduction to Meteorology
1 23/2 ̊N
In summary, themost important reasons for variations in the amount of solar energy reaching a
particular location are the seasonal changes in the angle at which the Sun’s rays strike the surface and
changes in the length of daylight.
Earth’s Orientation
What causes fluctuations in Sun angle and length of day- light during the course of a year? Variations
occur because Earth’s orientation to the Sun continually changes. Earth’s axis (the imaginary line through
the poles around which Earth rotates) is not perpendicular to the plane of its orbit around the Sun—
called the plane of the ecliptic. Instead, it is tilted 23 1/2° from the perpendicular, called the inclination
of the axis. If the axis were not inclined, Earth would lack seasons. Because the axis remains pointed in the same direction (toward the North Star), the orienta-tion of Earth’s axis to the Sun’s rays is
constantly chang- ing (Figure 2–5).
For example, on one day in June each year, Earth’s position in orbit is such that the Northern
Hemisphere is “leaning” 23 1/2° toward the Sun (left in Figure 2–5). Six months later, in December,
when Earth has moved to the opposite side of its orbit, the Northern Hemisphere “leans” 23 1/2° away
from the Sun (Figure 2–5, right). On days be-tween these extremes, Earth’s axis is leaning at amounts
less than 23 1/2° to the rays of the Sun. This change in orientation causes the spot where the Sun’s rays
are ver-tical to make an annual migration from 23 1/2° north of the equator to 23 1/2° south of the
equator. In turn, this migration causes the angle of the noon Sun to vary by up
Atmosphere
Sun’s rays
90 ̊
661/2 ̊
0 ̊23/2 ̊
30 ̊
1
S
Figure 2–4 Rays striking Earth at a low angle (near the poles) must traverse more of the atmosphere
than rays striking at a high angle (around the equator) and thus are subject to greater depletion by
reflection and absorption.
It is important to remember that Earth’s shape is spheri- cal. Hence, on any given day, the only places
that will re- ceive vertical (90°) rays from the Sun are located along one particular line of latitude. As we
move either north or south of this location, the Sun’s rays strike at decreasing angles. Thus, the nearer a
place is situated to the latitude receiving the vertical rays of the Sun, the higher will be its noon Sun, and
the more concentrated will be the radiation it receives.
Arctic Circle Tropic of Cancer Equator
Tropic of Capricorn
Equinox
March 21-22
Sun vertical at equator
Sun
231/2 ̊Solstice December 21-22 Sun vertical at Latitude 231/2 ̊ S
Solstice
June 21-22
Sun vertical at Latitude 231/2 ̊N
Figure 2–5 Earth–Sun relationships.
Orbit
Equinox
September 22-23
Sun vertical at equator
TABLE 2–1 Distance Radiation Must Travel Through the Atmosphere
Chapter 2 Heating Earth’s Surface and Atmosphere 39 Students Sometimes Ask . . .
Is the Sun ever directly overhead anywhere in the
United States?
Yes, but only in the state of Hawaii. Honolulu, located on the island of Oahu at about 21° north latitude,
experiences a 90° Sun angle twice each year—once at noon on about May 27 and again at noon on
about July 20. All of the other states are located north of the Tropic of Cancer and therefore never
experience the vertical rays of the Sun.
Solstices and Equinoxes
Based on the annual migration of the direct rays of the Sun, four days each year are especially significant.
On June 21 or 22, the vertical rays of the Sun strike 23 1/2° north latitude (23 1/2° north of the equator),
a line of latitude known as the Tropic of Cancer (Figure 2–5). For people living in the Northern
Hemisphere, June 21 or 22 is known as the summer solstice, the first “official” day of summer (see Box
2–1).
Six months later, on December 21 or 22, Earth is in an opposite position, with the Sun’s vertical rays
striking at 23 1/2° south latitude. This line is known as the Tropic of Capricorn. For those in the Northern
Hemisphere, December 21 or 22 is the winter solstice, the first day of winter. However,
N
Angle of Sun Above Horizon
Equivalent Number of Atmospheres Sunlight Must Pass Through
90° (directly overhead) 1.00
80° 1.02
70° 1.06 60° 1.15
50° 1.31
40° 1.56
30° 2.00
20° 2.92
10° 5.70
5° 10.80
0° (at horizon) 45.00
to 47° 123 1/2 1 23 1/22 for many locations during a year. A midlatitude city such as New York, for
instance, has a maximum noon Sun angle of 73 1/2° when the Sun’s verti- cal rays have reached their
farthest northward location in June and a minimum noon Sun angle of 26 1/2° six months later ( Figure
2–6).
Data:
Location: 40° N
Date: December 22 Location of 90° Sun: 231/2° S
Calculations:
Step 1:
Distance in degrees between 231/2° S and 40° N = 631/2°
Step 2:
90
–631/2°
261/2° = Noon Sun angle at 40° N
on December 22
Sun’s rays
Sun’s rays
90 ̊
261/2 ̊ 631/2°
Figure 2–6 Calculating the noon Sun angle. Recall that on any given day, only one latitude receives
vertical (90°) rays of the Sun. A place located 1° away (either north or south) receives an 89° angle; a
place 2° away, an 88° angle; and so forth. To calculate the noon Sun angle, simply find the number of
degrees of latitude separating the location you want to know about from the latitude that is receiving
the vertical rays of the Sun. Then subtract that value from 90°. The example in this figure illustrates how
to calculate the noon Sun angle for a city located at 40° north latitude on December 22 (winter solstice).
S Location: 40° N Tropic of Cancer (231/2 ̊N)
Equator (0°)
Tropic of Capricorn (231/2 ̊ S)
40 The Atmosphere: An Introduction to Meteorology
Box 2-1 When Are the Seasons?
Have you ever been caught in a snowstorm around Thanksgiving, even though winter does not begin
until December 21? Or per- haps you have endured several consecutive days of 100° temperatures
although sum- mer has not “officially” started? The idea of dividing the year into four seasons originated
from the Earth–Sun relationships discussed
in this chapter (Table 2–A). This astronomi- cal definition of the seasons defines winter (Northern
Hemisphere) as the period from the winter solstice (December 21–22) to the spring equinox (March 21–
22) and so forth. This is also the definition used most widely by the news media, yet it is not unusual for
portions of the United States and Canada to have significant snowfalls weeks before the “official” start
of winter (Table 2–A).
Because the weather phenomena we normally associate with each season do not coincide well with the
astronomical seasons, meteorologists prefer to divide the year into four three-month periods based
primarily on temperature. Thus, winter is defined as December, January, and Febru- ary, the three
coldest months of the year
in the Northern Hemisphere. Summer is defined as the three warmest months, June, July, and August.
Spring and autumn are
the transition periods between these two seasons (Figure 2–A). Inasmuch as these four three-month
periods better reflect the temperatures and weather that we associate with the respective seasons, this
definition
of the seasons is more useful for meteoro- logical discussions.
TABLE 2–A
Occurrence of the Seasons in the Northern Hemisphere
Season Astronomical Season
Spring March 21 or 22 to June 21 or 22
Summer June 21 or 22 to September 22 or 23 Autumn September 22 or 23 to December 21 or 22
Winter December 21 or 22 to March 21 or 22
Climatological Season March, April, May
June, July, August
September, October, November December, January, February
on this same day people in the Southern Hemisphere are experiencing their summer solstice.
The equinoxes occur midway between the solstices. September 22 or 23 is the date of the autumnal (fall)
equi- nox in the Northern Hemisphere, and March 21 or 22 is the date of the spring equinox (also called
the vernal equinox). On these dates the vertical rays of the Sun strike the equator (0° latitude) because
Earth’s position is such that its axis is tilted neither toward nor away from the Sun.
The length of daylight versus darkness is also deter- mined by the position of Earth relative to the Sun’s
rays. The length of daylight on June 21, the summer solstice in the Northern Hemisphere, is greater than
the length of night.
This fact can be established by examining Figure 2–7, which illustrates the circle of illumination—that is,
the boundary separating the dark half of Earth from the lighted half. The length of daylight is established
by comparing the fraction of a line of latitude that is on the “day” side of the circle of illumination with
the fraction on the “night” side. Notice that on June 21 all locations in the Northern Hemisphere experience
longer periods of daylight than darkness (Figure 2–7). By contrast, during the December
solstice the length of darkness exceeds the length of daylight at all locations in the Northern Hemisphere.
For example, consider New York City (about 40° north latitude), which has about 15 hours of daylight on
June 21 and only 9 hours on December 21.
Trees turning bright colors before losing their leaves is a common fall scene in the middle latitudes.
(Photo by Corbis/SuperStock).
FIGURE 2–A
Chapter 2 Heating Earth’s Surface and Atmosphere 41
24 hrs.
(a) June Solstice (Northern Hemisphere summer)
Sun’s rays
Sun’s rays
N
661/2 ̊
(b) December Solstice (Northern Hemisphere winter)
Also note from Table 2–2 that the farther north a loca-tion is from the equator on June 21, the longer
the period of daylight. When you reach the Arctic Circle (66 1/2° north latitude), the length of daylight is 24 hours. Places located at or north of the Arctic Circle experience the “midnight Sun,” which does not
set for a period that ranges from one day to about six months (Figure 2–8).
As a review of the characteristics of the summer sol-stice for the Northern Hemisphere, examine Figure
2–7 and Table 2–2 and consider the following:
1. The date of occurrence is June 21 or 22.
2. The vertical rays of the Sun are striking the Tropic of
3. Cancer (23 1/2° north latitude).
4. Locations in the Northern Hemisphere are experiencing their longest length of daylight and
highest Sun angle. (The opposite is true for the Southern Hemisphere.)
5. The farther north a location is from the equator, the longer the period of daylight, until the
Arctic Circle is reached, where the length of daylight becomes 24 hours. (The opposite is true
for the Southern Hemisphere.)
6. The winter solstice facts are the reverse. It should now
be apparent why a midlatitude location is warmest in the summer—when the days are longest and the
angle of the Sun is highest.
During an equinox (meaning “equal night”), the length of daylight is 12 hours everywhere on Earth
because the circle
of illumination passes directly through the poles, thus dividing the lines of latitude in half.
These seasonal changes, in turn, cause the month-to- month variations in temperature observed at most
locations outside the tropics. Figure 2–9 shows mean monthly temper- atures for selected cities at
different latitudes. Notice that the cities located at more poleward latitudes experience larger
temperature differences from summer to winter than do cit- ieslocated nearer the equator. Also notice
that temperature minimums for Southern Hemisphere locations occur in July,
S
40 ̊231/2 ̊
0 ̊
231/2 ̊ 40 ̊
(c) Spring/Fall Equinox
Figure 2-7 Characteristics of the solstices and equinoxes.
TABLE 2–2 Length of Daylight
Latitude (degrees) Summer Solstice
Winter Solstice
Equinoxes
0 12 hr 12 hr 12 hr
10 12 hr 35 min 11 hr 25 min 12 hr
20 13 hr 12 min 10 hr 48 min 12 hr
30 13 hr 56 min 10 hr 04 min 12 hr
40 14 hr 52 min 9 hr 08 min 12 hr
50 16 hr 18 min 7 hr 42 min 12 hr
60 18 hr 27 min 5 hr 33 min 12 hr
70 2 mo 0 hr 00 min 12 hr
80 4 mo 0 hr 00 min 12 hr
90 6 mo 0 hr 00 min 12 hr
40 ̊231/2 ̊
15 hrs. 131/2 hrs.
S
0 ̊
12 hrs.
231/2 ̊ 40 ̊
101/2 hrs. 9 hrs.
661/2 ̊
24 hrs.
661/2 ̊
661/2 ̊
S
N
131/2 hrs. 15 hrs.
231/2 ̊ 40 ̊
9 hrs. 101/2 hrs.
40 ̊231/2 ̊
12 hrs. 0 ̊
N
661/2 ̊
e
l
c
r
i
C
A
r
t
i
c
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2
h
r
.
1
2
h
r
c
n
r
r a r
s
f
C
a
o
e
T
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o
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i
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o
1
2
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r
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.
o
t
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E
q u
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2
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s
n
h
c
i
r
p
r
.
T
r
o
p
i
c
o
f
1
2
h
r
s .
Figure 2–8 Multiple exposures of the midnight Sun representative of midsummer in the high latitudes.
This example shows the midnight Sun in Norway. (Photo by Martin Woike/agephotostock)
whereas they occur in January for most places in the North- ern Hemisphere.
40
36
All locations situated at the same latitude have identical
Sun angles and lengths of daylight. If the Earth–Sun relationships
previously described were the only controls of
temperature, we would expect these places to have identical
temperatures as well. Obviously, such is not the case. 12 Although the angle of the Sun above the
horizon and the
length of daylight are the primary controls of temperature,
other factors must be considered—a topic that will be addressed
in Chapter 3. 0
100 itos, Per
St. Louis, Missouri 39 ̊N
Capetown South Afric
34 ̊
Wi
S
nnip
Manitoba 50° N
Point Barrow,
Alaska 71 ̊N
, a
Iqu
eg,
4 ̊S
u In summary, seasonal fluctuations in the amount of solar energy
reaching various places on Earth’s surface are caused by the 32 migrating vertical rays of the Sun
and the resulting variations in
Sun angle and length of daylight. 28
90 80 70 60 50 40 30 20 10 0 –10 –20
N D
Concept Check 2.1
 1 Do the annual variations in Earth–Sun distance adequately
 account for seasonal temperature changes? Explain.
 2 Use a simple sketch to show why the intensity of solar radiation striking Earth’s surface
changes when the Sun angle changes.
24 20 16
8 4
–4
–8 –12 –16 –20 –24 –28
 3 Briefly explain the primary cause of the seasons. –32 J
 4 What is the significance of the Tropic of Cancer and the
 Tropic of Capricorn?
 5 After examining Table 2–2, write a general statement that relates the season, latitude, and
the length of daylight.
F
M
A
M
J Month
A
S
O 42
Figure 2–9 Mean monthly temperatures for five cities located at different latitudes. Note that Cape
Town, South Africa, experiences winter in June, July, and August.
J
Temperature ( ̊C)
Temperature ( ̊F)
Chapter 2 Heating Earth’s Surface and Atmosphere 43
Students Sometimes Ask . . .
Where Is the Land of the Midnight Sun?
Any place located north of the Arctic Circle (66 1/2° north latitude) or south of the Antarctic Circle (66
1/2° south latitude) experiences 24 hours of continuous daylight (or darkness) at least one day each year.
The closer a place is to a pole, the longer the period of continuous daylight (or darkness). Someone
stationed
at either pole will experience six months of continuous daylight followed by six months of darkness.
Thus, the Land of the Midnight Sun refers to any location where the latitude is greater than 66 1/2°,
such as the northern portions of Alaska, Canada, Russia, and Scandinavia, as well as most of Antarctica.
Energy, Temperature, and Heat
The universe is made up of a combination of matter and energy. The concept of matter is easy to grasp
because it is the “stuff” we can see, smell, and touch. Energy, on the other hand, is abstract and
therefore more difficult to describe and understand. Energy comes to Earth from the Sun in the form of
electromagnetic radiation, which we see as light and feel as heat. There are countless places and
situations where energy is present—in the food we eat, the water located at the top of a waterfall, and
the waves that break along the shore.
Forms of Energy
Energy can be defined simply as the capacity to do work. Work is done whenever matter moves.
Common examples include the chemical energy from gasoline that powers
This image, which shows the first sunrise of 2008
at the South Pole, was taken at the U.S. Amundsen–Scott Station. At the moment the Sun cleared the
horizon, the weathered American flag was seen whipping in the wind above a sign marking the location
of the geographic South Pole. (NASA)
Question 1 What was the approximate date that this photograph was taken?
Question 2 How long after this photo was taken did the Sun set at the South Pole? Question 3 Over the course of one year, what is the highest position the Sun can reach (measured in
degrees) at the South Pole? On what date does this occur?
automobiles, the heat energy from stoves that excites water molecules (boils water), and the
gravitational energy that has the capacity to move snow down a mountain slope in the form of an
avalanche. These examples illustrate that energy takes many forms and can also change from one form
to another. For example, the chemical energy in gaso- line is first converted to heat in the engine of an
automobile, which is then converted to mechanical energy that moves the automobile along.
You are undoubtedly familiar with some of the com- mon forms of energy, such as heat, chemical,
nuclear, radi- ant (light), and gravitational energy. Energy is also placed into one of two major categories:
kinetic energy and potential energy.
Kinetic Energy Energy associated with an object by virtue of its motion is described as kinetic energy. A
simple ex- ample of kinetic energy is the motion of a hammer when driving a nail. Because of its motion,
the hammer is able to move another object (do work). The faster the hammer is swung, the greater its
kinetic energy (energy of motion). Similarly, a larger (more massive) hammer possesses more kinetic
energy than a smaller one, provided that both are swung at the same velocity. Likewise, the winds
associated with a hurricane possess much more kinetic energy than do light, localized breezes because
they are both larger in scale (cover a larger area) and travel at higher velocities.
Kinetic energy is also significant at the atomic level. All matter is composed of atoms and molecules that
are con-tinually vibrating, and by virtue of this motion have kinetic energy. For example, when a pan of
water is placed over a fire, the water becomes warmer because the fire causes the water molecules to
vibrate faster. Thus, when a solid, liq- uid, or gas is heated, its atoms or molecules move faster and
possess more kinetic energy.
44 The Atmosphere: An Introduction to Meteorology
Potential Energy As the termimplies, potential energy has the capability to do work. For example, large
hailstones suspended by an updraft in a towering cloud have potential energy. Should the updraft
subside, these hailstones may fall to Earth and do destructive work on roofs and vehicles. Many
substances, including wood, gasoline, and the food you eat, contain potential energy, which is capable
of doing work given the right circumstances.
Temperature
Humans think of temperature as how warm or cold an object is with respect to some standard measure.
However, our senses are often poor judges of warm and cold (see Students Sometimes Ask, p. 46).
Temperature is a measure of the average kinetic energy of the atoms or molecules in a sub-stance.
When a substance gains energy, its particles move faster and its temperature rises. By contrast, when
energy is lost, the atoms and molecules vibrate more slowly and its temperature drops. In the United
States the Fahrenheit scale is used most often for everyday expressions of tem- perature. However, scientists and the majority of other countries use the Celsius and Kelvin temperature scales. A discussion
of these scales is provided in Chapter 3.
It is important to note that temperature is not a meas- ure of the total kinetic energy of an object. For
example, a cup of boiling water has a much higher temperature than a bathtub of lukewarm water.
However, the quantity of water in the cup is small, so it contains far less kinetic en- ergy than the water
in the tub. Much more ice would melt in the tub of lukewarm water than in the cup of boiling water. The
temperature of the water in the cup is higher because the atoms and molecules are vibrating faster, but
the total amount of kinetic energy (also called thermal en- ergy) is much smaller because there are
fewer particles.
Students Sometimes Ask . . .
What would the seasons be like if Earth were not tilted
on its axis?
The most obvious change would be that all locations on the globe would experience 12 hours of daylight
every day of the year. Moreover, for any latitude, the Sun would always follow the path it does during
an equinox. There would be no seasonal temperature changes, and daily temperatures would be
roughly equivalent to the “average” for that location.
Heat
We define heat as energy transferred into or out of an object because of temperature differences
between that object and its sur-roundings. If you hold a hot mug of coffee, your hand will begin to feel
warm or even hot. By contrast, when you hold an ice cube, heat is transferred from your hand to the ice
cube. Heat flows from a region of higher temperature to one
of lower temperature. Once the temperatures become equal, heat flow stops.
Meteorologists further subdivide heat into two catego-ries, latent heat and sensible heat. Latent heat is
the energy involved when water changes from one state of matter to another—when liquid water
evaporates and becomes water vapor, for example. During evaporation heat is required to break the
hydrogen bonds between water molecules that occurs when water vapor escapes a water body.
Because the most energetic water molecules escape, the average kinetic energy (temperature) of the
water body drops. Therefore, evaporation is a cooling process, something you may have experienced
upon stepping out, dripping wet, from a swim- ming pool or bathtub. The energy absorbed by the
escaping water vapor molecules is termed latent heat (meaning “hid- den”) because it does not result in
a temperature increase. The latent heat stored in water vapor is eventually released in the atmosphere
during condensation—when water vapor returns to the liquid state during cloud formation. There- fore,
latent heat is responsible for transporting consider- able amounts of energy from Earth’s land–sea
surface to the atmosphere.By contrast, sensible heat is the heat we can feel and measure with a thermometer. It is called sensible
heat be- cause it can be “sensed.” Warm air that originates over the Gulf of Mexico and flows into the
Great Plains in the winter is an example of the transfer of sensible heat.
Concept Check 2.2
1 Distinguish between heat and temperature.
2 Describe how latent heat is transferred from Earth’s land–sea surface to the atmosphere.
3 Compare latent heat and sensible heat.
Mechanisms of Heat Transfer
Heating Earth’s Surface and Atmosphere ATMOSPHERE ▸Solar Radiation
The flow of energy can occur in three ways: conduction, convection, and radiation (Figure 2–10).
Although they are presented separately, all three mechanisms of heat transfer can operate
simultaneously. In addition, these processes may transfer heat between the Sun and Earth and between
Earth’s surface, the atmosphere, and outer space.
Conduction
Anyone who attempts to pick up a metal spoon left in a boiling pot of soup realizes that heat is
transmitted along the entire length of the spoon. The transfer of heat in this manner is called conduction.
The hot soup causes the mol- ecules at the lower end of the spoon to vibrate more rapidly.
Conduction
tains numerous air spaces that impair the flow of heat. This is why wild animals may burrow into a
snowbank to escape the “cold.” The snow, like a down-filled comforter, does not supply heat; it simply
retards the loss of the animal’s own body heat.
Convection
Much of the heat transport in Earth’s atmosphere and oceans occurs by convection. Convection is heat
transfer that involves the actual movement or circulation of a sub-stance. It takes place in fluids (liquids
such as water and gases such as air) where the material is able to flow.
The pan of water being heated over a campfire in Figure 2–10 illustrates the nature of a simple
convective circula-tion. The fire warms the bottom of the pan, which conducts heat to the water inside.
Because water is a relatively poor conductor, only the water in close proximity to the bottom of the pan
is heated by conduction. Heating causes water to expand and become less dense. Thus, the hot, buoyant
water near the bottom of the pan rises, while the cooler, denser water above sinks. As long as the water
is heated from the bottom and cools near the top, it will continue to “turn over,” producing a convective
circulation. In a similar manner, some of the air in the lowest layer of the atmosphere that was heated by radiation
and conduc-tion is transported by convection to higher layers of the at- mosphere. For example, on a
hot, sunny day the air above a plowed field will be heated more than the air above the surroundi ng
woodlands. As warm, less dense air above the plowed field buoys upward, it is replaced by the cooler air
above the woodlands (Figure 2–11). In this way a convec-tive flow is established. The warm parcels of
rising air are called thermals and are what hang-glider pilots use to keep their crafts soaring. Convection
of this type not only trans- fers heat but also transports moisture aloft. The result is an increase in
cloudiness that frequently can be observed on warm summer afternoons.
Figure 2–11 (a) Heating of Earth’s surface produces thermals of rising air that transport heat and
moisture aloft. (b) The rising air cools, and
if it reaches the condensation level, clouds form. Rising warmer air and descending cooler air are an
example of convective circulation.
Chapter 2 Heating Earth’s Surface and Atmosphere 45
Convection
Figure 2–10 The three mechanisms of heat transfer: conduction, convection, and radiation.
These molecules and free electrons collide more vigorously with their neighbors and so on up the
handle of the spoon. Thus, conduction is the transfer of heat through electron and molecular collisions
from one molecule to another. The ability of substances to conduct heat varies considerably. Metals are
good conductors, as those of us who have touched a hot spoon have quickly learned. Air, in contrast, is a
very poor conductor of heat. Consequently, conduction is impor-tant only between Earth’s surface and
the air immediately in contact with the surface. As a means of heat transfer for the atmosphere as a
whole, conduction is the least signifi- cant and can be disregarded when considering most meteorological
phenomena.
Objects that are poor conductors, such as air, are called insulators. Most objects that are good insulators,
such as cork, plastic foam, or goose down, contain many small air spaces. The poor conductivity of the
trapped air gives these materials their insulating value. Snow is also a poor conductor (good insulator),
and like other insulators, it conSolar
heating
Radiation
Condensation level
(a)
(b)
Rising thermal Convection
Convection
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46 The Atmosphere: An Introduction to Meteorology
On a much larger scale is the global convective circu- lation of the atmosphere, which is driven by the
unequal heating of Earth’s surface. These complex movements are responsible for the redistribution of
heat between hot equa-torial regions and frigid polar latitudes and will be dis- cussed in detail in
Chapter 7.
Students Sometimes Ask . . .
In the morning when I get out of bed, why does the tile flooring in the bathroom feel much colder than
the carpeted area, even though both materials are the same temperature? The difference you feel is
due mainly to the fact that floor tile
is a much better conductor of heat than carpet. Hence, heat is more rapidly conducted from your bare
feet to the tile floor than from your bare feet to the carpeted floor. Even at room tempera-ture (20°C
[68°F]), objects that are good conductors can feel chilly to the touch. (Remember, body temperature is
about 37°C [98.6°F].)
Atmospheric circulation consists of vertical as well as horizontal components, so both vertical and
horizontal heat transfer occurs. Meteorologists often use the term convection to describe the part of the
atmospheric circulation that in- volves upward and downward heat transfer. By contrast, the term
advection is used to denote the primarily horizontal component of convective flow. (The common term
for ad- vection is “wind,” a phenomenon we will examine closely in later chapters.) Residents of the
midlatitudes often expe-rience the effects of heat transfer by advection. For example, when frigid
Canadian air invades the Midwest in January, it brings bitterly cold winter weather.
Micrometers
Radiation
The third mechanism of heat transfer is radiation. Unlike conduction and convection, radiation is the
only mecha- nism of heat transfer that can travel through the vacuum of space and thus is responsible
for solar energy reaching Earth.
Solar Radiation The Sun is the ultimate source of en- ergy that drives the weather machine. We know
that the Sun emits light and heat energy as well as the rays that darken skin pigmentation. Although
these forms of energy constitute a major portion of the total energy that radiates from the Sun, they are
only a part of a large array of energy called radiation, or electromagnetic radiation. This array or
spectrum of electromagnetic energy is shown in Figure 2–12. All types of radiation, whether X-rays, radio waves, or heat waves, travel through the vacuum of space
at 300,000 kilometers (186,000 miles) per second, a value known as the speed of light. To help visualize
radiant energy, imagine rip- ples made in a calm pond when a pebble is tossed in. Like the waves
produced in the pond, electromagnetic waves come in various sizes, or wavelengths—the distance from
one crest to the next (Figure 2–12). Radio waves have the longest wavelengths, up to tens of kilometers
in length. Gamma waves are the shortest, at less than one-billionth of a centimeter long. Visible light is
roughly in the middle of this range.
Radiation is often identified by the effect that it pro- duces when it interacts with an object. The retinas
of our eyes, for instance, are sensitive to a range of wavelengths called visible light. We often refer to
visible light as white light because it appears “white” in color. It is easy to show, however, that white
light is really an array of colors, each color corresponding to a specific range of wavelengths. By using a
prism, white light can be divided into the colors
Microwave FM UHF
VHF AM VLF
Radio
0.4 0.5
0.6
0.7
Infrared Near Far
1 100 Micrometers
100 GHz
1 GHz
Visible
“Hard”
“Soft”
X rays
Gamma rays
Wavelength
(meters) 10–14
10–12 10–10 10–8
10–6 10–4 10–2
1
102 104
Figure 2–12 The electromagnetic spectrum, illustrating the wavelengths and names of various types of
radiation.
Ultraviolet Near Far
Figure 2–13 Visible light consists of an array of colors we commonly call the “colors of the rainbow.”
Rainbows are relatively common phenomena produced by the bending and reflection of light by drops
of water. There is more about rainbows in Chapter 16. (Photo by David Robertson/Alamy)
of the rainbow, from violet with the shortest wavelength, 0.4 micrometer (μm) (1 micrometer is one –
millionth of a meter), to red with the longest wavelength, 0.7 micrometer (Figure 2–13).
Located adjacent to the color red, and having a longer wavelength, is infrared radiation, which cannot
be seen by the human eye but is detected as heat. Only the infrared en- ergy that is nearest the visible
part of the spectrum is intense
It is important to note that the Sun emits all forms of ra- diation, as shown in Figure 2–12, but in varying
quantities. Over 95 percent of all solar radiation is emitted in wave-lengths between 0.1 and 2.5
micrometers, with much of this energy concentrated in the visible and near-infrared parts of the
electromagnetic spectrum (Figure 2–14). The narrow band of visible light, between 0.4 and 0.7
micrometer, represents over 43 percent of the total energy emitted. The bulk of the remainder lies in
the infrared zone (49 percent) and ultravio- let (UV) section (7 percent). Less than 1 percent of solar radiation
is emitted as X-rays, gamma rays, and radio waves.
Laws of Radiation
To obtain a better appreciation of how the Sun’s radiant energy interacts with Earth’s atmosphere and
land–sea surface, it is helpful to have a general understanding of the basic radiation laws. Although the
mathematics of these laws is beyond the scope of this text, the concepts are fun- damental to
understanding radiation:
1. All objects continually emit radiant energy over a range of wavelengths.* Thus, not only do hot
objects such as the Sun continually emit energy, but Earth does as well, even the pol ar ice caps.
*The temperature of the object must be above a theoretical value called absolute zero (–273°C) in order
to emit radiant energy. The letter K is used for values on the Kelvin temperature scale. For more
explanation, see the section on “Temperature Scales” in Chapter 3.
Chapter 2 Heating Earth’s Surface and Atmosphere 47 enough to be felt as heat and is referred to On the opposite side of the visible range, located next to
violet, the energy emitted is called ultraviolet radiation and consists of wavelengths that may cause
sunburned skin.
Although we divide radiant energy into categories based on our ability to perceive them, all wavelengths
of radiation behave similarly. When an object absorbs any form of electromagnetic energy, the waves
ex- cite subatomic particles (electrons). This results in an increase in molecular motion and a
corresponding increase in tempera-ture. Thus, electromagnetic waves from the Sun travel through
space and, upon being absorbed, increase the molecular motion of other molecules—including those
that make up the atmosphere, Earth’s land–sea surfaces, and human bodies.
One important difference among the various wavelengths of radiant energy is that shorter wavelengths
are more energetic. This accounts for the fact that relatively short (high-energy) ultraviolet waves can
damage human tissue more readily than can similar exposures to longer-wavelength radiation. The
damage can result in skin cancer and cataracts.
as near infrared.
43%
0.5
Radiation from Sun (10,000°F)
49%
1.0
Shortwave
Radiation emitted from Earth (59°F)
10 20 30 40 50
Longwave
7%
0.1
Ultra- Visible violet
1.5
Wavelength in micrometers
2.0 Infrared
Figure 2–14 Comparison of the intensity of solar radiation and radiation emitted by Earth. Because of
the Sun’s high surface temperature, most of its energy is radiated at wavelengths shorter than 4 micrometers, with the greatest intensity in the visible range of the electromagnetic spectrum. Earth, in
contrast, radiates most of its energy in wavelengths longer than 4 micrometers, primarily in the infrared
band. Thus, we call the Sun’s radiation shortwave and Earth’s radiation longwave. (From PHYSICAL
GEOGRAPHY: A LANDSCAPE APPRECIATION, 9th Edition, by Tom L. McKnight and Darrell Hess, © 2008.
Reprinted by permission of Pearson Education, Inc., Upper Saddle River, NJ.)
Radiation intensity
48 The Atmosphere: An Introduction to Meteorology
Box 2-2 Radiation Laws Gregory J. Carbone*
All bodies radiate energy. Both the rate and the wavelength of radiation emitted depend on the
temperature of the radiating body.
Stefan–Boltzmann Law
This law mathematically expresses the rate of radiation emitted per unit area:
E 5 sT4
E, the rate of radiation emitted by a body, is proportional to the fourth power
of the body’s temperature (T). The Stefan–Boltzmann constant 1s2 is equal to
5.67 3 1028 W/m2 K4. Compare the dif- ference between the radiation emission from the Sun and Earth.
The Sun, with an average temperature of 6000 K, emits 73,483,200 watts per square meter 1Wm222:
E 5 15.67 3 1028W/m2K4216000K24 5 73,483,200W/m2
By contrast, Earth has an average temper- ature of only 288 K. If we round the value to 300 K, we have:
E 5 15.67 3 1028W/m2K421300K24 5 459W/m2
The Sun has a temperature that is approximately 20 times higher than that of Earth and thus it emits
approximately 160,000 times more radiation per unit area. This makes sense because
204 5 160,000.
Wien’s Displacement Law
Wien’s displacement law describes mathematically the relationship between the temperature (T) of a
radiating body and its wavelength of maximum emission 1lmax2:
Wien’s constant (C) is equal to 2898 mmK. If we use the Sun and Earth as examples, we find:
2898 mmK
lmax1Sun2 5 6000K 5 0.483mm
and: l 1Earth2 5 2898mmK 5 9.66mm max 300 K
Note that the Sun radiates its maximum energy within the visible portion of the electromagnetic
spectrum. The cooler Earth radiates its maximum energy in the infrared portion of the electromagnetic
spectrum.
*Professor Carbone is a faculty member in the Department of Geography at the University of South
Carolina.
emitters of radiation. For some wavelengths the atmo-sphere is nearly transparent (little radiation
absorbed). For others, however, it is nearly opaque (absorbs most of the radiation that strikes it).
Experience tells us that the atmosphere is quite transparent to visible light emit-ted by the Sun because
it readily reaches Earth’s surface.
To summarize, although the Sun is the ultimate source of ra- diant energy, all objects continually radiate
energy over a range of wavelengths. Hot objects, such as the Sun, emit mostly shortwave (high-energy)
radiation. By contrast, most objects at everyday temperatures (Earth’s surface and atmosphere) emit
longwave (low-energy) radiation. Objects that are good absorbers of radia-tion, such as Earth’s surface,
are also good emitters. By contrast, most gases are good absorbers (emitters) only in certain wavelengths
but poor absorbers in other wavelengths.
Concept Check 2.3
 1 Describe the three basic mechanisms of energy transfer.
 Which mechanism is least important meteorologically?
 2 What is the difference between convection and advection?
 3 Compare visible, infrared, and ultraviolet radiation. For each, indicate whether it is considered
shortwave or longwave radiation.
 4 In what part of the electromagnetic spectrum does the Sun radiate maximum energy? How
does this compare to Earth?
 5 Describe the relationship between the temperature of a radiating body and the wavelengths
it emits.
7. Hotter objects radiate more total energy per unit area than do colder objects. The Sun, which
has a surface temperature of 6000 K (10,000°F), emits about 160,000 times more energy per
unit area than does Earth, which has an average surface temperature of 288 K (59°F). (This
concept is called the Stefan–Boltzmann law and is expressed mathematically in Box 2–2.)
8. Hotter objects radiate more energy in the form of short-wavelength radiation than do cooler
objects. We can visualize this law by imagining a piece of metal that, when heated sufficiently
(as occurs in a blacksmith’s shop), produces a white glow. As it cools, the metal emits more of
its energy in longer wavelengths and glows a reddish color. Eventually, no light is given off,
but if you place your hand near the metal, the still lon- ger infrared radiation will be
detectable as heat. The Sun radiates maximum energy at 0.5 micrometer, which is in the visible range (Figure 2–14). The maximum radiation emitted from Earth occurs at a
wavelength of 10 microm- eters, well within the infrared (heat) range. Because the maximum
Earth radiation is roughly 20 times longer than the maximum solar radiation, it is often
referred to as longwave radiation, whereas solar radiation is called shortwave radiation. (This
concept, known as Wien’s dis- placement law, is expressed mathematically in Box 2–2.)
9. Objects that are good absorbers of radiation are also good emitters. Earth’s surface and the
Sun are nearly perfect radiators because they absorb and radiate with nearly 100 percent
efficiency. By contrast, the gases that compose our atmosphere are selective absorbers and
lmax 5 C/T
Most people welcome sunny weather. On warm days, when the sky is cloudless and bright, many spend
a great deal of time outdoors “soaking up” the sunshine (Figure 2–B). For many, the goal is to develop a
dark tan, one that sunbathers often describe as “healthy looking.” Ironically, there is strong evidence
that too much sunshine (specifically, too much ultraviolet radiation) can lead to seri- ous health
problems, mainly skin cancer and cataracts of the eyes.
Since June 1994 the National Weather Service (NWS) has issued the next-day ultraviolet index (UVI) for
the United States to warn the public of potential health risks of exposure to sunlight ( Figure 2–C). The
UV index is determined by taking into account the predicted cloud cover and reflectivity of the surface,
as well as the
Sun angle and atmospheric depth for each forecast location. Because atmospheric ozone strongly
absorbs ultraviolet radiation, the extent of the ozone layer is also con-sidered. The UVI values lie on a
scale from 0 to 15, with larger values representing greatest risk.
The U.S. Environmental Protection Agency has established five exposure categories
FIGURE 2–B Exposing sensitive skin to too much solar ultraviolet radiation has potential health risks.
(Photo by Eddie Gerald/Rough Guides)
based on UVI values— Low, Moderate, High, Very High, and Extreme (Table 2–B). Precau-tionary
measures have been developed for each category. The public is advised to minimize outdoor activities
when the
The Ultraviolet Index*
UV Index
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
UVI is Very High or
Extreme. Sunscreen
with a sun-protection
factor (SPF) of 15 or
higher is recommended
for all exposedskin. This is especially
important after swimming
or while sunbathing, even
on cloudy days with the UVI in the Low category.
The public is advised to minimize outdoor activities when the UVI is Very High or Extreme.
Table 2–B shows the range of minutes
to burn for the most susceptible skin type (pale or milky white) for each exposure cat- egory. Note that
the exposure that results in sunburn varies from over 60 minutes for the Low category to less than 10
minutes for the Extreme category. It takes approximately five
June 8, 2008
Chapter 2 Heating Earth’s Surface and Atmosphere 49
TABLE2–B TheUVIndex:MinutestoBurnfortheMostSusceptibleSkinType Exposure
Minutes to Burn
. 60 40–60 25–40 10–25 , 10
UVI Value
0–2 3–5 6–7 8–10 11–15
Category
Low Moderate High Very High Extreme
Description
Low danger from the Sun’s UV rays for the average person.
Moderate risk from unprotected Sun exposure. Take precautions during the midday, when Sun is
strongest.
Protection against sunburn is needed. Cover up, wear a hat and sunglasses, and use sunscreen.
Try to avoid the Sun between 11 am and 4 pm. Otherwise, cover up and use sunscreen.
Take all precautions. Unprotected skin will burn in minutes. Do not pursue outdoor activities if possible.
If outdoors, apply sunscreen liberally every 2 hours.
FIGURE 2–C UV index forecast for June 8, 2008. To view the current UVI forecast, go to
www.epa.gov/sunwise/uvindex.html. times longer to cause sunburn of the least susceptible skin type, brown to dark. The most susceptible
skin type develops red sun- burn, painful swelling, and skin peeling when exposed to excessive sunlight.
By contrast, the least susceptible skin type rarely burns and shows very rapid tanning response.
*Based on material prepared by Professor Gong-Yuh Lin, a faculty member in the Department of
Geography at California State University, Northridge.
50 The Atmosphere: An Introduction to Meteorology What Happens to Incoming
Solar Radiation?
Heating Earth’s Surface and Atmosphere ATMOSPHERE ▸What Happens to Incoming Solar Radiation?
When radiation strikes an object, three different things may occur simultaneously. First, some of the
energy may be absorbed. Recall that when radiant energy is absorbed, the molecules begin to vibrate
faster, which causes an increase in temperature. The amount of energy absorbed by an object depends
on the intensity of the radiation and the object’s absorptivity. In the visible range, the degree of
absorptivity is largely responsible for the brightness of an object. Surfaces that are good absorbers of all
wavelengths of visible light appear black in color, whereas light-colored surfaces have a much lower
absorptivity. That is why wearing light-colored clothing on a sunny summer day may help keep you
cooler. Second,substances such as water and air, which are transpar- ent to certain wavelengths of
radiation, may simply transmit energy—allowing it to pass through without being absorbed. Third, some
radiation may “bounce off” the object without being absorbed or transmitted. In summary, radiation
may be absorbed, transmitted, or redirected (reflected or scattered).
Figure 2–15 shows the fate of incoming solar radiation averaged for the entire globe. On average, about
50 percent of incoming solar energy is absorbed at Earth’s surface. An- other 30 percent is reflected and
scattered back to space by the atmosphere, clouds, and reflective surfaces such as snow and water, and
about 20 percent is absorbed by clouds and atmospheric gases.
(Figure 2–16b). Whether solar radiation is reflected or scat-tered depends largely on the size of the
intervening particles and the wavelength of the light.
Reflection and Earth’s Albedo About 30 percent of the solar energy that reaches our planet is reflected
back to space (Figure 2–15). Included in this figure is the amount sent skyward by backscattering. This
energy is lost to Earth and does not play a role in heating the atmosphere or Earth’s surface.
The fraction of radiation that is reflected by an object is called its albedo. The albedo for Earth as a
whole (planetary albedo) is 30 percent. The amount of light reflected from Earth’s land–sea surface
represents only about 5 percent of the total planetary albedo (Figure 2–15). Not surprisingly, clouds are
largely responsible for most of Earth’s “bright- ness” as seen from space. The high reflectivity of clouds is
experienced when looking down on a cloud during an air- line flight. In comparison to Earth, the Moon, which has neither clouds nor an atmosphere, has an average albedo
of only 7 percent. Although a full Moon appears bright, the much brighter and larger Earth would, by
comparison, provide far more light for an astronaut’s “Earth-lit” Moon walk at night.
Figure 2–17 gives the albedos for various surfaces. Fresh snow and thick clouds have high albedos (good
reflectors). By contrast, dark soils and parking lots have low albedos and thus absorb much of the
radiation they receive. In the case of a lake or the ocean, note that the angle at which the Sun’s rays
strike the water surface greatly affects its albedo.
What determines whether solar radiation will be transmitted to the surface, scattered, reflected back to
space, or absorbed by the gases and parti- cles in the atmosphere? As you will see, it depends greatly
upon the wavelength of the radiation, as well as the size and nature of the intervening material.
Reflection and Scattering
Reflection is the process whereby light bounces back from an object at the same angle and inten-sity
(Figure 2–16a). By contrast, scattering pro- duces a larger number of weaker rays, traveling in different
directions. Scattering disperses light both forward and backward (backscattering)
Figure 2–15 Average distribution of incoming solar radiation, by percentage. More solar energy is
absorbed by Earth’s surface than by the atmosphere.
Solar radiation 100%
30% lost to space by reflection and scattering
5% backscattered to space by the atmosphere
20% reflected from clouds
20% of radiation absorbed by atmosphere and clouds
50% of direct and diffused radiation absorbed by land and sea
5% reflected from land–sea surface
(a) (b)
Figure 2–16 Reflection and scattering. (a) Reflected light bounces back from a surface at the same angle
at which it strikes that surface and with the same intensity. (b) When a beam of light is scattered, it
results in a larger number of weaker rays, traveling in different directions. Usually more energy is
scattered in the forward direction than is backscattered.
Scattering and Diffused Light Although incoming solar radiation travels in a straight line, small dust
particles and gas molecules in the atmosphere scatter some of this energy in different directions. The
result, called diffused light, explains how light reaches the area under the limbs of a tree and how a
room is lit in the absence of direct sun- light. Further, on clear days scattering accounts for the brightness and the blue color of the daytime sky. In con-trast, bodies like the Moon and Mercury, which
are with- out atmospheres, have dark skies and “pitch-black” shadows, even during daylight hours.
Overall, about one-half of solar radiation that is absorbed at Earth’s surface arrives as diffused
(scattered) light.
Blue Skies and Red Sunsets Recall that sunlight ap- pears white, but it is composed of
all colors. Gas molecules more effectively
scatter blue and violet light
that have shorter wavelengths than they scatter red and orange. This ac- counts for the blue color of the
sky and the orange and red colors seen at sunrise and sunset (Figure 2–18). On clear days, you can look
in any direction away from the direct Sun and see a blue sky, the wavelength of light more readily
scattered by the atmosphere.
Conversely, the Sun appears to have an orange-to-reddish hue when viewed near the horizon (Figure 2–
19). This is the result of the great distance solar radiation must travel through the atmosphere before it
reaches your eyes (see Table 2–1). During its travel, most of the blue and violet
Light roof 35–50%
Asphalt 5–10%
Dark roof 10–15%
Wet plowed field 15–25%
Sandy beach 20–40%
Scattering
Reflection
Grass
Chapter 2 Heating Earth’s Surface and Atmosphere 51
Thick clouds 70–80%
Forest 5–25% 5–10%
Water
5–80%
(varies with sun angle)
Figure 2–17 Albedo (reflectivity) of various surfaces. In general, light-colored surfaces tend to be more
reflective than dark-colored surfaces and thus have higher albedos. wavelengths are scattered out. Consequently, the light that reaches your eyes consists mostly of reds
and oranges. The reddish appearance of clouds during sunrise and sunset also results because the
clouds are illuminated by light from which the blue color has been removed by scattering.
Figure 2–18 At sunset, clouds often appear red because they are illuminated by sunlight in which most
of the blue light has been lost due to scattering. (Photo by Michael Collier)
Thin clouds 25–30%
Snow 50–90%
52
The Atmosphere: An Introduction to Meteorology
Midday sun
Absorption of Solar Radiation
Although Earth’s surface is a relatively good absorber (effectively absorbing most wave -lengths of solar
radiation), the atmosphere is not. As a result, only 20 percent of the solar radi- ation that reaches Earth
is absorbed by gases in the atmosphere (see Figure 2–15). Much of the remaining incoming solar
radiation transmits through the atmosphere and is absorbed by the Earth’s land–sea surface. The
atmosphere is a less effective absorber because gases are selecMidday–
observer sees whitish sun, blue sky
Sunset– observer sees reddish sunset
Sun at sunset
tive absorbers (and emitters) of radiation.
Freshly fallen snow is another example of a selective absorber. Snow is a poor absorber of visible light
(reflecting up to 85 percent) and, as a result, the temperature directly above a snow-covered sur- face is
colder than it would otherFigure
2–19 Short wavelengths (blue and violet) of visible light are scattered more effectively than are
longer wavelengths
(red and orange). Therefore, when the Sun is overhead, an observer can look in any direction and see
predominantly blue light that was selectively scattered by the gases in the atmosphere. By contrast, at
sunset, the path that light must take through the atmosphere is much longer. Consequently, most of the
blue light
is scattered before it reaches an observer. Thus, the Sun appears reddish in color.
The most spectacular sunsets occur when large quan-tities of fine dust or smoke particles penetrate the
strato-sphere. For three years after the great eruption of the Indonesian volcano Krakatau in 1883, brilliant sunsets oc- curred worldwide. In addition, the European summer that followed this colossal
explosion was cooler than normal, which has been attributed to the loss of incoming solar ra- diation
due to an increase in backscattering.
Large particles associated with haze, fog, and smog scat-ter light more equally in all wavelengths.
Because no color is predominant over any other, the sky appears white or gray on days when large
particles are abundant. Scattering of sunlight by haze, water droplets, or dust particles makes it possible
for us to observe bands (or rays) of sunlight called crepuscular rays. These bright fan-shaped bands are
most commonly seen when the Sun shines through a break in the clouds, as shown in Figure 2–20.
Crepuscular rays can also be observed around twilight, when towering clouds cause alter- nating lighter
and darker bands (light rays and shadows) to streak across the sky.
In summary, the color of the sky gives an indication of the number of large or small particles present.
Numerous small par-ticles produce red sunsets, whereas large particles produce white (gray) skies. Thus,
the bluer the sky, the less polluted, or dryer, the air.
wise be because much of the incoming radiation is reflected away. By contrast, snow is a very good
absorber (absorbing up to 95 percent) of
the infrared (heat) radiation that is emitted from Earth’s sur- face. As the ground radiates heat upward,
the lowest layer of snow absorbs this energy and, in turn, radiates most of the energy downward. Thus,
the depth at which a winter’s frost can penetrate into the ground is much less when the ground is snow
covered than in an equally cold region with- out snow—giving credence to the statement “The ground is
blanketed with snow.” Farmers who plant winter wheat de-sire a deep snow cover because it insulates
their crops from bitter winter temperatures.
Figure 2–20 Crepuscular rays are produced when haze scatters light. Crepuscular rays are most
commonly seen when the Sun shines through a break in the clouds. (Photo by Tetra Images/ Jupiter
Images)
Chapter 2 Heating Earth’s Surface and Atmosphere 53
Concept Check 2.4
 1 Prepare and label a simple sketch that shows what happens
 to incoming solar radiation.
 2 Why does the daytime sky usually appear blue?
 3 Why may the sky have a red or orange hue near sunrise or sunset?
 4 What is the primary factor that causes the albedo of
some materials to vary depending on their location or time of day?
Eye on the Atmosphere This image was taken by astronauts aboard the International Space Station
as it traveled over the west coast of South America. On average, these astro- nauts experience 16
sunrises and sunsets during a 24-hour orbital period. The separation between day and night is marked
by a line called the terminator (NASA).
Question 1 Locate the terminator in this image. Would you describe it as a sharp line? Explain.
Question 2 Are the astronauts looking at a sunrise or a sunset?
The Role of Gases in the Atmosphere
Earth’s surface is emitted at wavelengths between 2.5 and 30 micrometers, placing it in the long end of
the infra-red band of the electromagnetic spectrum. Heating of the atmosphere requires an
understanding of how gases interact with the short wavelength incoming solar radia-tion and the long
wavelength outgoing radiation emitted by Earth (Figure 2–21, top).
Heating the Atmosphere
When a gas molecule absorbs radiation, this energy is transformed into internal molecular motion,
which is detectable as a rise in temperature (sensible heat). The lower part of Figure 2–21 gives the
absorptivity of the principal atmospheric gases. Note that nitrogen, the most
Radiation emitted by Earth
100%
0% 100%
0% 100%
0%
Nitrogen N2
Carbon dioxide CO2
Solar radiation
100%
Oxygen and
Water vapor H2O
0% 0.1
ozone O2 and O3
0.2 0.3 0.4 0.6 0.8 1 1.5 2 Visible radiation
Ultra- Visible violet
Shortwave radiation
3 4 5 6 8 10 20 30
Atmospheric window
Infrared
Longwave radiation
ATMOSPHERE
Heating Earth’s Surface and Atmosphere ▸The Greenhouse Effect
Figure 2–21 The effectiveness of selected gases of the atmosphere in absorbing incoming shortwave
radiation (left side of graph) and outgoing longwave terrestrial radiation (right side). The blue areas
represent the percentage of radiation absorbed by the various gases. The atmosphere
as a whole is quite transparent to solar radiation between
0.3 and 0.7 micrometer, which includes the band of visible light. Most solar radiation falls in this range,
explaining why
a large amount of solar radiation penetrates the atmosphere and reaches Earth’s surface. Also, note
that longwave infrared radiation in the zone between 8 and 12 micrometers can escape the atmosphere
most readily. This zone is called the atmospheric window.
Figure 2–21 shows that the majority of solar radiation is emitted in wavelengths shorter than 2.5
micrometers— shortwave radiation. By contrast, most radiation from
Absorptivity
Radiation intensity
54 The Atmosphere: An Introduction to Meteorology
abundant constituent in the atmosphere (78 percent), is a relatively poor absorber of incoming solar
radiation. The only significant absorbers of incoming solar radiation are water vapor, oxygen, and ozone,
which account for most of the solar energy absorbed directly by the atmosphere. Oxygen and ozone are
efficient absorbers of high-energy, shortwave radiation. Oxygen removes most of the shorterwavelength
UV radiation high in the atmosphere, and ozone absorbs UV rays in the stratosphere
between 10 and 50 kilometers (6 and 30 miles). The absorption of UV energy in the stratosphere
accounts for the high tempera-tures experienced there. More importantly, without the removal of most
UV radiation, human life would not be possible because UV energy disrupts our genetic code. Looking at the bottom of Figure 2–21, you can see that for the atmosphere as a whole, none of the
gases are ef- fective absorbers of radiation with wavelengths between 0.3 and 0.7 micrometer. This
region of the spectrum corre-sponds to the visible light band, which constitutes about 43 percent of the
energy radiated by the Sun. Because the atmosphere is a poor absorber of visible radiation, most of this
energy is transmitted to Earth’s surface. Thus, we say that the atmosphere is nearly transparent to
incoming solar ra- diation and that direct solar energy is not an effective “heater” of Earth’s atmosphere.
Students Sometimes Ask . . .
What causes leaves on deciduous trees to change color
each fall?
The leaves of all deciduous trees contain the pigment chlorophyll, which gives them a green color. The
leaves of some trees also contain the pigment carotene, which is yellow, and still others pro- duce a
class of pigments that appear red in color. During summer, leaves are factories that generate sugar from
carbon dioxide and water by the action of light on chlorophyll. As the dominant pig- ment, chlorophyll
causes the leaves of most trees to appear green. The shortening days and cool nights of autumn trigger
changes in deciduous trees. With a drop in chlorophyll production, the green color of the leaves fades,
allowing other pigments to be seen. If the leaves contain carotene, as do birch and hickory, they will
change to bright yellow. Other trees, such as red maple and sumac, display the brightest reds and
purples in the autumn landscape.
We can also see in Figure 2–21 that the atmosphere is generally a relatively efficient absorber of
longwave (infra-red) radiation emitted by Earth (see the bottom right of Figure 2–21). Water vapor and
carbon dioxide are the prin- cipal absorbing gases, with water vapor absorbing about 60 percent of the
radiation emitted by Earth’s surface. There- fore, water vapor, more than any other gas, accounts for
the warm temperatures of the lower troposphere, where it is most highly concentrated.
Although the atmosphere is an effective absorber of ra- diation emitted by Earth’s surface, it is
nevertheless quite
transparent to the band of radiation between 8 and 12 mi- crometers. Notice in Figure 2–21 (lower right)
that the gases in the atmosphere (N2, CO2, H2O) absorb minimal energy in these wavelengths. Because
the atmosphere is transparent to radiation between 8 and 12 micrometers, much as win- dow glass is
transparent to visible light, this band is called the atmospheric window. Although other “atmospheric
windows” exist, the one located between 8 and 12 micro- meters is the most significant because it is
located where Earth’s radiation is most intense.
By contrast, clouds that are composed of tiny liquid droplets (not water vapor) are excellent absorbers
of the en- ergy in the atmospheric window. Clouds absorb outgoing radiation and radiate much of this
energy back to Earth’s surface. Thus, clouds serve a purpose similar to window blinds because they
effectively block the atmospheric win- dow and lower the rate at which Earth’s surface cools. This
explains why nighttime temperatures remain higher on cloudy nights than on clear nights. Because the atmosphere is largely transparent to solar (shortwave) radiation but more absorptive of the
longwave radiation emitted by Earth, the atmosphere is heated from the ground up. This explains the
general drop in tempera- ture with increased altitude in the troposphere. The farther from the “radiator”
(Earth’s surface), the colder it gets. On average, the temperature drops 6.5°C for each kilometer (3.5°F
per 1000 feet) increase in altitude, a figure known as the normal lapse rate. The fact that the
atmosphere does not acquire the bulk of its energy directly from the Sun but is heated by Earth’s
surface is of utmost importance to the dy- namics of the weather machine.
The Greenhouse Effect
Research of “airless” planetary bodies such as the Moon have led scientists to determine that if Earth
had no atmo-sphere, it would have an average surface temperature below freezing. However, Earth’s
atmosphere “traps” some of the outgoing radiation, which makes our planet habitable. The extremely
important role the atmosphere plays in heating Earth’s surface has been named the green- house effect.
As discussed earlier, cloudless air is largely transparent to incoming shortwave solar radiation and,
hence, trans- mits it to Earth’s surface. By contrast, a significant frac-tion of the longwave radiation
emitted by Earth’s land–sea surface is absorbed by water vapor, carbon dioxide, and other trace gases in
the atmosphere. This energy heats the air and increases the rate at which it radiates energy, both out to
space and back toward Earth’s surface. Without this complicated game of “pass the hot potato,” Earth’s
average temperature would be –18°C (0°F) rather than the current temperature of 15°C (59°F) (Figure
2–22). These absorptive gases in our atmosphere make Earth habitable for humans and other life forms.
This natural phenomenon was named the greenhouse effect because greenhouses are heated in a
similar manner
Incoming shortwave solar radiation
Incoming shortwave solar radiation
All outgoing longwave energy
is reradiated directly back to space
Some outgoing longwave radiation absorbed by greenhouse gases
Greenhouse gases reradiate some energy Earthward
(a) Airless bodies like the Moon
Figure 2–22 The greenhouse effect. (a) All incoming solar radiation reaches the surface of airless bodies
such as the Moon. However, all of the energy that is absorbed by the surface is radiated directly back to
space. This causes the lunar surface
to have a much lower average surface temperature than Earth. Because the Moon experiences days
and nights that are about
2 weeks long, the lunar days are hot and the nights are frigid.
(b) On bodies with modest amounts of greenhouse gases, suchas Earth, much of the short-wavelength radiation from the Sun passes through the atmosphere and is
absorbed by the surface. This energy is then emitted from the surface as longer-wavelength radiation,
which is absorbed by greenhouse gases in the atmosphere. Some of the energy absorbed will be
radiated back to the surface and is responsible for keeping Earth’s surface
33°C (59°F) warmer than it would be otherwise. (c) Bodies
with abundant greenhouse gases, such as Venus, experience extraordinary greenhouse warming, which
is estimated to raise its surface temperature by 523°C (941°F).
(Figure 2–22). The glass in a greenhouse allows shortwave solar radiation to enter and be absorbed by
the objects in-side. These objects, in turn, radiate energy but at longer wavelengths, to which glass is
nearly opaque. The heat, therefore, is “trapped” in the greenhouse. Although this analogy is widely used,
it has been shown that air inside greenhouses attains higher temperatures than outside air in part due
to the restricted exchange of warmer air inside and cooler air outside. Nevertheless, the term
“greenhouse ef- fect” is still used to describe atmospheric heating.
Media reports frequently and erroneously identify the greenhouse effect as the “villain” in the global
warm- ing problem. However, the greenhouse effect and global warming are different concepts. Without
the greenhouse ef- fect, Earth would be uninhabitable. Scientists have mount- ing evidence that human
activities (particularly the release of carbon dioxide into the atmosphere) are responsible for a rise in
global temperatures (see Chapter 14). Thus, hu-
(b) Bodies with modest amounts of greenhouse gases like Earth
Chapter 2 Heating Earth’s Surface and Atmosphere 55
Incoming shortwave solar radiation
Most outgoing longwave radiation absorbed by greenhouse gases
Greenhouse gases reradiate considerable energy toward the Venusian surface
(c) Bodies with abundant greenhouse gases like Venus
mans are compounding the effects of an otherwise natural process (the greenhouse effect). It is
incorrect to equate the greenhouse phenomenon, which makes life possible, with global warming—
which involves undesirable changes to our atmosphere caused by human activities.
Concept Check 2.5
1 Explain why the atmosphere is heated chiefly by radiation
from Earth’s surface rather than by direct solar radiation.
2 Which gases are the primary heat absorbers in the lower atmosphere? Which gas is most influential in
weather? 3 What is the atmospheric window? How is it “closed”? 4 How does Earth’s atmosphere act as a
greenhouse? 5 What is the “villain” in the global warming problem?
56 The Atmosphere: An Introduction to Meteorology Students Sometimes Ask . . .
Is Venus so much hotter than Earth because it is closer to
the Sun?
Proximity to the Sun is actually not the primary factor. On Earth, water vapor and carbon dioxide are the
primary greenhouse gases and are responsible for elevating Earth’s average surface tempera-ture by
33°C (59°F). However, greenhouse gases make up less than 1 percent of Earth’s atmosphere. By contrast,
the Venusian atmosphere is much denser and consists of 97 percent carbon dioxide. Thus, the Venusian
atmosphere experiences extraordinary greenhouse warming, which is estimated to raise its surface temperature
by 523°C (941°F)—hot enough to melt lead.
Earth’s Heat Budget
Globally, Earth’s average temperature remains relatively constant, despite seasonal cold spells and heat
waves. This stability indicates that a balance exists between the amount of incoming solar radiation and
the amount of radiation emitted back to space; otherwise, Earth would be getting progressively colder
or progressively warmer. The annual balance of incoming and outgoing radiation is called Earth’s heat
budget.
Annual Energy Balance
Figure 2–23 illustrates Earth’s annual energy budget. For sim- plicity we will use 100 units to represent
the solar radiation intercepted at the outer edge of the atmosphere. You have already seen that, of the
total radiation that reaches Earth, roughly 30 units (30 percent) are reflected and scattered back to
space. The remaining 70 units are absorbed, 20 units within the atmosphere and 50 units by Earth’s
land–sea sur- face. How does Earth transfer this energy back to space?
If all of the energy absorbed by our planet were radi- ated directly and immediately back to space,
Earth’s heat budget would be simple—100 units of radiation received and 100 units returned to space.
In fact, this does happen over time (minus small quantities of energy that become locked up in biomass
that may eventually become fossil fuel). What complicates the heat budget is the behavior of certain
greenhouse gases, particularly water vapor and carbon dioxide. As you learned, these greenhouse gases
absorb a large share of outward-directed infrared radia-tion and radiate much of that energy back to
Earth. This “recycled” energy significantly increases the radiation re- ceived by Earth’s surface. In
addition to the 50 units re- ceived directly from the Sun, Earth’s surface receives long- wave radiation
emitted downward by the atmosphere (94 units).
Incoming Solar Radiation
+100 units Outgoing radiation lost to space
–100 units –58 units
emitted to space by the atmosphere
+23 units
released to the atmosphere by condensation (latent heat)
+20 units
absorbed by atmosphere and clouds
+7 units
absorbed by the atmosphere
+8 units
of longwave radiation absorbed by the atmosphere
+50 units
of solar radiation absorbed by Earth’s surface
–7 units
lost from Earth’s surface by conduction and convection
+
–23 units
lost by evaporation
+
–20 units
lost by longwave =
radiation
Longwave energy exchange between Earth’s surface and the atmosphere
–50 units
of energy lost by Earth’s surface
–30 units
of solar radiation reflected back and scattered –12 units
of longwave radiation to which the atmosphere is transparent
to space
94 units
114 units
Heat budget of Earth and the atmosphere. These estimates of the average global energy budget come
from satellite observations and radiation studies. As more data are accumulated, these numbers will be
modified. (Data from Kiehl, Trenberth, Liou, and others)
Figure 2–23
Chapter 2 Heating Earth’s Surface and Atmosphere 57
This infrared (IR) image produced by the GOES-14 satellite displays cold objects as bright white and hot
objects as black. The hottest (blackest) features shown are land surfaces, and the coldest (whitest)
features are the tops of towering storm clouds. Re- call that we cannot see infrared (thermal) radiation,
but we have developed artificial detectors capable of extending our vision into the long-wavelength
portion of the electromagnetic spectrum.
Question 1 Several areas of cloud develop- ment and potential storms are shown on this
IR image. One is a well-developed tropical storm named Hurricane Bill. Can you locate Hurricane Bill?
Question 2 What is an advantage of IR images over visible images?
A balance is maintained because all the energy absorbed by Earth’s surface is returned to the
atmosphere and even-tually radiated back to space. Earth’s surface loses energy through a variety of
processes: the emission of longwave radiation; conduction and convection; and energy loss to Earth’s
surface through the process of evaporation—latent heat (Figure 2–23). Most of the longwave radiation
emitted skyward is re-absorbed by the atmosphere. Conduction re-sults in the transfer of energy
between Earth’s surface to the air directly above, while convection carries the warm air located near the
surface upward as thermals (7 units).
Earth’s surface also loses a substantial amount of en- ergy (23 units) through evaporation. This occurs
because energy is required for liquid water molecules to leave the
surface of a body of water and change to its gaseous form, water vapor. The energy lost by a water body
is carried into the atmosphere by molecules of water vapor. Recall that the heat used to evaporate
water does not produce a temperature change and is referred to as latent heat (hidden heat). If the
water vapor condenses to form cloud droplets, the energy will be detectable as sensible heat (heat we can feel and measure with a thermometer). Thus through the process of evaporation, water molecules
carry latent heat into the atmosphere, where it is eventually released.
In summary, a careful examination of Figure 2–23 confirms that the quantity of incoming solar radiation
is, over time, bal- anced by the quantity of longwave radiation that is radiated back to space.
58 The Atmosphere: An Introduction to Meteorology
Box 2-3 Solar Power
Nearly 95 percent of the world’s energy needs are derived from fossil fuels, primarily oil, coal, and
natural gas. Current estimates indicate that, at the present rate of consump-tion, we have enough fossil
fuels to last about 150 years. However, with the rapid increase in demand by developing coun-tries, the
rate of consumption continues to climb. Thus, reserves will be in short supply sooner rather than later.
How can a growing demand for energy be met without radically altering the planet we inhabit?
Although no clear answer has yet emerged, we must con-sider greater use of alternate energy sources,
such as solar and wind power.
The term solar energy generally refers to the direct use of the Sun’s rays to sup- ply energy for the needs
of people. The simplest, and perhaps most widely used, passive solar collectors are south-facing
windows. As shortwave sunlight passes through the glass, its energy is absorbed by objects in the room
that, in turn, radi- ate longwave heat that warms the air in the room.
More elaborate systems used for home heating involve active solar collectors. These roof-mounted
devices are normally large blackened boxes that are covered with glass. The heat they collect can be
trans- ferred to where it is needed by circulating air or fluids through pipes. Solar collectors are also
used successfully to heat water for domestic and commercial needs. In Israel, for example, about 80
percent of all homes are equipped with solar collectors that pro- vide hot water.
Research is currently under way to improve the technologies for concentrat- ing sunlight. One method
uses parabolic troughs as solar energy collectors. Each collector resembles a large tube that has been
cut in half. Their highly polished surfaces reflect sunlight onto a collection pipe. A fluid (usually oil) runs
through the pipe and is heated by the concentrated sunlight. The fluid can reach temperatures of over
400°F and is typically used to make steam that drives a turbine to pro- duce electricity.
Another type of collector uses photovol-taic (solar) cells that convert the Sun’s energy
FIGURE 2–D Nearly cloudless deserts, such as California’s Mojave Desert, are prime sites for photovoltaic
cells that convert solar radiation directly into electricity. (Photo by Jim West/Alamy)
directly into electricity. Photovoltaic cells are usually connected together to create solar panels in which
sunlight knocks electrons into higher-energy states, to produce electricity (Figure 2–D). For many years,
solar cells were used mainly to power calculators and novelty devices. Today, however, large
photovoltaic power stations are connected to electric grids to supplement other power- generating facilities. The leading countries in photovoltaic
capacity are Germany, Japan, Spain, and the United States. The high cost of solar cells makes generating
solar electric- ity more expensive than electricity created by other sources. As the cost of fossil fuels
continues to increase, advances in photo- voltaic technology should narrow the price differential.
A new technology being developed, called the Stirling dish, converts thermal energy to electricity by
using a mirror array to focus the Sun’s rays on the receiver end of a Stirling engine ( Figure 2–E). The
internal side of a receiver then heats hydrogen gas, causing it to expand. The pressure created by the
expanding gas drives a piston, which turns a small electric generator.
FIGURE 2–E This Stirling dish is located near Phoenix, Arizona. (Photo by Brian Green/Alamy)
Latitudinal Heat Balance
Because incoming solar radiation is roughly equal to the amount of outgoing radiation, on average,
worldwide temperatures remain constant. However, the balance of
incoming and outgoing radiation that is applicable for the entire planet is not maintained at each
latitude. Averaged over the entire year, a zone around Earth that lies within 38° latitude of the equator
receives more solar radiation than is lost to space (Figure 2–24). The opposite is true for higher latitudes,
where more heat is lost through radiation emitted by Earth than is received from the Sun.
We might conclude that the tropics are getting hotter and the poles are getting colder. But that is not
the case. In-stead, the global wind systems and, to a lesser extent, the oceans act as giant thermal
engines, transferring surplus heat from the tropics poleward. In effect, the energy imbal- ance drives the
winds and the ocean currents.
It should be of interest to those who live in the mid- dle latitudes—in the Northern Hemisphere, from
the lati-tude of New Orleans at 30° north to the latitude of Winni- peg, Manitoba, at 50° north—that
most heat transfer takes place across this region. Consequently, much of the stormy weather
experienced in the middle latitudes can be attrib- uted to this unending transfer of heat from the tropics
to- ward the poles. These processes are discussed in more de-tail in later chapters.
Concept Check 2.6
1 The tropics receive more solar radiation than is lost. Why
then don’t the tropics keep getting hotter?
2 What two phenomena are driven by the imbalance of heating that exists between the tropics and
poles?
Deficit
N. Pole
Chapter 2 Heating Earth’s Surface and Atmosphere 59 38° latitude
Equator
Outgoing radiation
Incoming radiation
Surplus
Figure 2–24 Latitudinal heat balance averaged over the entire year. In the zone extending 38° on both
sides of the equator, the amount of incoming solar radiation exceeds the loss from outgoing Earth
radiation. The reverse is true for the middle and high polar latitudes, where losses from outgoing Earth
radiation exceed gains from incoming solar radiation.
60 The Atmosphere: An Introduction to Meteorology
Give It Some Thought
1. How would our seasons be affected if Earth’s axis were not inclined 231° to the plane of its orbit but
were
6. Which of the three mechanisms of heat transfer is most significant in each of the following situations:
a. Driving a car with the seat heater turned on
b. Sitting in an outdoor hot tub
c. Lying inside a tanning bed
d. Driving a car with the air conditioning turned on
7. During a “shore lunch” on a fishing trip to a remote location, the fishing guide will sometimes place a
pail of lake water next to the cooking fire, as shown in the accompanying illustration. When the water in
the pail begins to boil, the guide will lift the pail from the fire and “impress” the guests by placing their
other hand on the bottom. Use what you have learned about the three mechanisms of heat transfer to
explain why the guide’s hands aren’t burned by touching the bottom of the pail.
2 instead perpendicular?
10. Describe the seasons if Earth’s axis were inclined 40°. Where would the Tropics of Cancer and
Capricorn be located? How about the Arctic and Antarctic Circles?
11. The accompanying four diagrams (labeled a–d) are intended to illustrate the Earth–Sun
relationships that produce the seasons.
12. a. Which one of these diagrams most accurately shows this relationship?
13. b. Identify what is inaccurately shown in each of the other three diagrams. 14. On what date is Earth closest to the Sun? On that date, what season is it in the Northern
Hemisphere? Explain this apparent contradiction.
15. When a person in the United States watches the Sun move through the sky during a typical
day, he or she sees it travel from left to right. However, on the same day, a person in Australia
will see the Sun travel across the sky from right to left. Explain or make a sketch that
illustrates why this difference occurs.
(NASA)
8. The Sun shines continually at the North Pole for six months, from the spring equinox until the fall
equinox, yet temperatures never get very warm. Explain why this is the case.
9. The accompanying image shows an area of our galaxy where stars having surface temperatures much
hotter than the Sun have recently formed. Imagine that an Earth-like planet formed around one of these
stars, at a distance where it receives the same intensity of light as Earth. Use the laws of radiation to
explain why this planet may not provide a habitable environment for humans.
HEATING EARTH’S SURFACE AND ATMOSPHERE IN REVIEW
Chapter 2 Heating Earth’s Surface and Atmosphere 61
16. Rank the following according to the wavelength of radiant energy each emits, from the
shortest wavelength to the longest:
17. a. A light bulb with a filament glowing at 4000°C b. A rock at room temperature
c. A car engine at 140°C
18. Figure 2–15 shows that about 30 percent of the
Sun’s energy is reflected or scattered back to space.
If Earth’s albedo were to increase to 50 percent, how would you expect Earth’s average
surface temperature to change?
19. Explain why Earth’s equatorial regions are not becoming warmer, despite the fact that they
receive more incoming solar radiation than they radiate back to space.
20. The accompanying photo shows the explosive 1991 eruption of Mount Pinatubo in the
Philippines. How would you expect global temperatures to respond to
the ash and debris this volcano spewed high into the atmosphere?
(U.S. Geological Survey)
 ● The seasons are caused by changes in the angle at which the Sun’s rays strike the surface and
the changes in the length of daylight at each latitude. These seasonal changes are the result of
the tilt of Earth’s axis as it revolves around the Sun.  ● Energy is the ability to do work. The two major categories
of energy are (1) kinetic energy, which can be thought of as energy of motion, and (2) potential
energy, energy that has the capability to do work.
 ● Temperature is a measure of the average kinetic energy of the atoms or molecules in a
substance.
 ● Heat is the transfer of energy into or out of an object because of temperature differences
between that object and its surroundings.
 ● Latent heat (hidden heat) is the energy involved when
water changes from one state of matter to another. During evaporation, for example, energy is
stored by the escaping water vapor molecules, and this energy is eventually released when
water vapor condenses to form water droplets in clouds.
 ● Conduction is the transfer of heat through matter by electron and molecular collisions
between molecules. Because air is a poor conductor, conduction is significant only between
Earth’s surface and the air immediately in contact with the surface.
 ● Convection is heat transfer that involves the actual movement or circulation of a substance.
Convection is an important mechanism of heat transfer in the atmosphere, where warm air rises
and cooler air descends.
 ● Radiation or electromagnetic radiation consists of a large array of energy that includes X-rays,
visible light, heat waves, and radio waves that travel as waves of various
sizes. Shorter wavelengths of radiation have greater
energy.
● These are four basic laws of radiation: (1) All objects emit
radiant energy; (2) hotter objects radiate more total energy per unit area than colder objects; (3) the
hotter the radiating body, the shorter is the wavelength of maximum radiation; and
(4) objects that are good absorbers of radiation are also good emitters.
● Approximately 50 percent of the solar radiation that strikes the atmosphere reaches Earth’s surface.
About
30 percent is reflected back to space. The fraction of radiation reflected by a surface is called its albedo.
The remaining 20 percent of the energy is absorbed by clouds and the atmosphere’s gases.
● Radiant energy absorbed at Earth’s surface is eventually radiated skyward. Because Earth has a much
lower surface temperature than the Sun, its radiation is in
the form of longwave infrared radiation. Because the atmospheric gases, primarily water vapor and
carbon dioxide, are more efficient absorbers of terrestrial (longwave) radiation, the atmosphere is
heated from the ground up.
● The selective absorption of Earth radiation by atmospheric gases, mainly water vapor and carbon
dioxide, that results in Earth’s average temperature being warmer than it would be otherwise is referred
to as the greenhouse effect. ● The greenhouse effect is a natural phenomenon that makes Earth habitable. Human activities that
release greenhouse gases (primarily carbon dioxide) are the “villains” of global warming—not the
“greenhouse effect” as it is often, but inaccurately, portrayed.
62
The Atmosphere: An Introduction to Meteorology
● ●
Because of the annual balance that exists between incoming and outgoing radiation, called the heat
budget, Earth’s average temperature remains relatively constant.
Averaged over the entire year, a zone around Earth between 38° north and 38° south receives more
solar radiation than is lost to space. The opposite is true for
higher latitudes, where more heat is lost through outgoing longwave radiation than is received. It is this
energy imbalance between the low and high latitudes that drives the weather system and in turn
transfers surplus heat from the tropics poleward.
absorptivity (p. 50)
advection (p. 46)
albedo (p. 50)
aphelion (p. 36)
atmospheric window (p. 54) autumnal (fall) equinox (p. 40) backscattering (p. 50)
circle of illumination (p. 40) conduction (p. 45) convection (p. 45)
diffused light (p. 51) energy (p. 43)
greenhouse effect (p. 54) heat (p. 44)
VOCABULARY REVIEW
heat budget (p. 56)
inclination of the axis (p. 38)
infrared radiation (p. 47)
kinetic energy (p. 43)
latent heat (p. 44)
longwave radiation (p. 48)
perihelion (p. 36)
plane of the ecliptic (p. 38)
potential energy (p. 44)
radiation, or electromagnetic radiation (p. 46) reflection (p. 50)
revolution (p. 36)
rotation (p. 36)
scattering (p. 50) PROBLEMS
sensible heat (p. 44) shortwave radiation (p. 48) spring (vernal) equinox (p. 40) summer solstice (p. 39)
temperature (p. 44)
thermal (p. 45)
Tropic of Cancer (p. 39) Tropic of Capricorn (p. 39) ultraviolet radiation (p. 47) visible light (p. 46)
wavelength (p. 46)
winter solstice (p. 39)
21. Refer to Figure 2–6 and calculate the noon Sun angle on
June 21 and December 21 at 50° north latitude, 0° latitude (the equator), and 20° south
latitude. Which of these latitudes has the greatest variation in noon Sun angle between
summer and winter?
22. For the latitudes listed in Problem 1, determine the length of daylight and darkness on June 21
and December 21 (refer to Table 2–2). Which of these latitudes has the largest seasonal
variation in length of daylight? Which latitude has the smallest variation?
23. Calculate the noon Sun angle at your location for the equinoxes and solstices.
24. If Earth had no atmosphere, its longwave radiation emission would be lost quickly to space,
making the planet approximately 33 K cooler. Calculate the rate
of radiation emitted (E), and the wavelength of maximum radiation emission 1lmax2 for Earth
at 255 K. (Hint: See Box 2–2.)
25. The intensity of solar radiation can be calculated using trigonometry, as shown in Figure 2–25.
For simplicity, consider a solar beam of 1 unit width. The surface area over which the beam
would be spread changes with Sun angle, such that:
26. Surface area 5 1 unit sin1Sun angle2
Sun’s rays
Sun angle Surface area
Figure 2–25 Calculating solar intensity. Therefore, if the Sun angle at solar noon is 56°:
1 unit 1 unit
Surface area 5 sin 56° 5 0.829 5 1.206 units
Using this method and your answers to Problem 3, calculate the intensity of solar radiation (surface area)
for your location at noon during the summer and winter solstices.
1 unit
6. Figure 2–26 is an analemma—a graph used to determine the
latitude where the overhead noon Sun is located for any date.
To determine the latitude of the overhead noon Sun from the 22° analemma, find the desired date on
the graph and read the 20° coinciding latitude along the left axis. Determine the latitudeof the overhead noon Sun for the following dates. Remember
to indicate north (N) or south (S).
14° a. March 21 12°
June
May
July
April
b. June 5
c. December 10
7. Use Figure 2–6 and the analemma in Figure 2–26 to calculate the noon Sun angle at your location
(latitude) on the following dates:
a. September 7 b. July 5
c. January 1
10° 8° 6° 4° 2° 0°
10 5 510
30 15 25 20
20 25 15
5 105
15 30
August
Latitude of Vertical Noon Sun
September
March
October
February
November
January December
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Surface and Atmosphere.
N 24°
18°
16°
30 20
10 20 3010 20
30
Chapter 2 Heating Earth’s Surface and Atmosphere 63
231/2° 0°
1 23 /2°
25
20
4°5 10
20
25
2°30 15


10°
12°
14°
16°
18°
20° 22°
24° S
10
25
5
25 20
15 20
25 30
5 10
15 20
The analemma
25 20
15 10 5
30
Figure 2–26
30
15
5 10 15
20 25
30
10 5
10
Temperature
Temperature is one of the basic elements of weather and climate. When someone asks what the
weather is like outside, air temperature is often the first element we mention. From everyday
experience, we know that temperatures vary on different time scales: seasonally, daily, and even hourly.
Moreover, we all realize that substantial temperature differences exist from one place to another. In
Chapter 2 you learned how air is heated and examined the role of Earth–Sun relationships in causing temperature variations from season to season and from latitude to latitude. In this chapter you will
focus on several other aspects of
this very important atmospheric property, including factors other than Earth– Sun relationships, that act
as temperature controls. You will also look at how temperature is measured and expressed and see that
temperature data can be of very practical value to us all. Applications include calculations that are useful
in evaluating energy consumption, crop maturity, and human comfort.
Death Valley, California. Summertime temperatures here
are among the highest anywhere in the Western Hemisphere. For more about Death Valley’s
extraordinary temperatures, see Box 3–1. (Photo by Michael Collier)
After completing this chapter you should be able to:
 Calculate five commonly used types of temperature data and interpret a map that depicts
temperature data using isotherms.
 List the principal controls of temperature and use examples to describe their effects.
 Explain why water and land heat and cool differently.
 Interpret the patterns depicted on world maps of January and July temperatures and on a world
map of annual temperature ranges.
Discuss the basic daily and annual cycles of air temperature.
Explain how different types of thermometers work and why the placement of thermometers is an
important factor in obtaining accurate readings.
Distinguish among Fahrenheit, Celsius, and Kelvin temperature scales.
Discuss the concept of apparent temperature and compare two basic indices that are expressions of this
idea.
65
66 The Atmosphere: An Introduction to Meteorology For the Record:
Air-Temperature Data
Temperature Data and the Controls of Temperature ATMOSPHERE ▸Basic Temperature Data
Temperatures recorded daily at thousands of weather sta-tions worldwide provide much of the
temperature data compiled by meteorologists and climatologists (Figure 3–1). Hourly temperatures may
be recorded by an observer or ob-tained from automated observing systems that continually monitor
the atmosphere. At many locations only the maxi- mum and minimum temperatures are obtained see
(Box 3–1).
Basic Calculations The daily mean temperature is determined by averaging the 24 hourly readings or by adding the
maximum and minimum temperatures for a 24-hour period and dividing by 2. From the maximum and
minimum, the daily temperature range is computed by finding the difference between these figures.
Other data involving longer periods are also compiled:
 The monthly mean temperature is calculated by adding together the daily means for each day
of the month and dividing by the number of days in the month.
 The annual mean temperature is an average of the 12 monthly means.
 The annual temperature range is computed by finding the difference between the warmest
and coldest monthly mean temperatures.
 Mean temperatures are especially useful for making daily, monthly, and annual comparisons. It
is common to hear a weather reporter state, “Last month was the warmest Febru- ary on record”
or “Today Omaha was 10° warmer than Chi- cago.” Temperature ranges are also useful statistics
because they give an indication of extremes, a necessary part of under-standing the weather
and climate of a place or an area.
 (a)
Isotherms
To examine the distribution of air temperatures over large ar- eas, isotherms are commonly used. An
isotherm is a line that connects points on a map that have the same temperature (iso 5 ”equal,” therm
5 ”temperature”). Therefore, all points through which an isotherm passes have identical temperatures
for the time period indicated. Generally, isotherms representing 5° or 10° temperature differences are
used, but any interval may be chosen. Figure 3–2 illustrates how isotherms are drawn on a map. Notice
that most isotherms do not pass directly through the observing stations because the station readings
may not co- incide with the values chosen for the isotherms. Only an occa-sional station temperature
will be exactly the same as the value of the isotherm, so it is usually necessary to draw the lines by
estimating the proper position between stations.
Isothermal maps are valuable tools because they clearly make temperature distribution visible at a
glance. Areas of low and high temperatures are easy to pick out. In addi-tion, the amount of
temperature change per unit of distance, called the temperature gradient, is easy to visualize. Closely
spaced isotherms indicate a rapid rate of temperature change, whereas more widely spaced lines
indicate a more gradual rate of change. For example, notice in Figure 3–2 that the isotherms are more
closely spaced in Colorado and Utah (steeper temperature gradient), whereas the isotherms are spread
farther apart in Texas (gentler temperature gra- dient). Withoutisotherms a map would be covered with
numbers representing temperatures at tens or hundreds of places, which would make patterns difficult
to see.
Concept Check 3.1 1 How are the following temperature data calculated: daily mean, daily range, monthly mean, annual
mean, and annual range?
2 What are isotherms, and what is their purpose?
(b)
Figure 3–1 People living in the middle latitudes can experience a wide range of temperatures during a
year. (a) Pedestrian navigating through a Chicago neighborhood during a February 2011 blizzard that
dropped more than 50 centimeters (nearly 20 inches) of snow on the city. (Photo by Zuma
Press/Newscom) (b) Beating the heat on a hot summer day. (Photo by mylife photos/Alamy).
50s
20s
40s
70s
10s
40s
60s 70s
30s
80s 90s
Figure 3–2
Vancouver 49
Portland 56
Sacramento 63
Calgary 22
Regina 30 13 20
Bismarck 19
40
Ely 42
Casper 24
Des Moines Peoria Scottsbluff 42 55 60
50
Toronto
Boston Albany 57
Las Vegas
60 59 50
Topeka 54
Louisville 66
72
Palm Springs 72
57 Albuquerque 65
70
Little Rock 75
Houston 83
80
50s
Students Sometimes Ask…
What’s the hottest city in the United States?
It depends on how you define “hottest.” If average annual tem- perature is used, then Key West, Florida,
is the hottest, with an annual mean of 25.6°C (78°F) for the 30-year span 1971–2000. However, if we
look at cities with the highest July maximums
during the 1971–2000 span, then the desert community of Palm Springs, California, has the distinction
of being hottest. Its average daily high in July is a blistering 42.4°C (108.3°F)! Yuma, Arizona
(41.7°C/107°F), Phoenix, Arizona (41.4°C/106°F), and Las Vegas, Nevada (40°C/104.1°F), aren’t far
behind.
Why Temperatures Vary: The Controls of Temperature
Temperature Data and the Controls of Temperature ATMOSPHERE ▸Controls of Temperature The controls of temperature are factors that cause temper- atures to vary from place to place and from
time to time. Chapter 2 examined the most important cause for tempera-ture variation—differences in
the receipt of solar radiation. Because variations in Sun angle and length of daylight
depend on latitude, they are responsible for warm temper- atures in the tropics and colder
temperatures poleward. Of course, seasonal temperature changes at a given latitude occur as the Sun’s
vertical rays migrate toward and away from a place during the year. Figure 3–3 reminds us of the
importance of latitude as a control of temperature.
But latitude is not the only control of temperature. If it were, we would expect all places along the same
paral- lel to have identical temperatures. This is clearly not the case. For instance, Eureka, California, and
New York City are both coastal cities at about the same latitude, and both places have an annual mean
temperature of 11°C (51.8°F). Yet New York City is 9.4°C (16.9°F) warmer than Eureka in July and 9.4°C
(16.9°F) colder than Eureka in January. In another example, two cities in Ecuador—Quito and
Guayaquil—are relatively close to one another, but the mean annual temperatures at these two cities
differ by 12.2°C (22°F). To explain these situations and countless others, we must realize that factors
other than latitude also exert a strong influence on temperature. In the next sections we examine these
other controls, which include:
Differential heating of land and water Ocean currents
Altitude
Geographic position
Cloud cover and albedo
32
40
Fargo 23
Milwaukee 52
20
Missoula 36
30
40
Duluth 31
50
59
Cleveland 62 Charleston
Montreal 46
Bangor 47
Denver 41
6070 Gallup
Tucson 76
Lubbock 76
80
90 Monterrey
93
Montgomery 83
57 Philadelphia
64
Raleigh 78
Myrtle Beach 81
Miami 85
Map showing high temperatures for a spring day. Isotherms are lines that connect points of equal
temperature. Showing temperature distribution in this way makes patterns easier to see. Notice that
most isotherms do not pass directly through the observing stations. It is usually necessary to draw
isotherms by estimating their proper position between stations. On television and in many newspapers,
temperature maps are in color. Rather than labeling isotherms, the area between isotherms is labeled.
For example, the zone between the 60° and 70° isotherms is labeled “60s.”
Chapter 3 Temperature 67
68
The Atmosphere: An Introduction to Meteorology
40
36
32 90 28 80 24
Surface temperatures in the Pacific Ocean are much lower. The peaks of the Sierra Nevada, still capped
with snow, form a cool blue line down the eastern side of California.
In side-by-side bodies of land and water, such as is shown in Figure 3–4, land heats more rapidly and to
higher tem- peratures than water, and it cools more rapidly and to lower tem- peratures than water.
Variations in air temperatures, there- fore, are much greater over land than over water. Why do land
and water heat and cool differently? Several factors are responsible.
R
Mbandaka, ep. of Congo
0.01 ́N
Moscow,
Russia 55° 45 ́N
Mia
Flor 25 ̊4
Auckland,
New Zealand 37 ̊43 ́S
mi, ida 5 ́N
20 16 12
8 4
70 60 50 40
1.
An important reason that the surface temperature of water rises and falls much more slowly than the
surface temperature of land is that water is highly mobile. As water is heated, convection distributes the
heat through a con-siderably larger mass. Daily temperature changes occur to depths of 6 meters (20
feet) or more below the surface, and yearly, oceans and deep lakes experience tempera-ture variations
through a layer between 200 and 600 me-ters (650 and 2000 feet) thick.
In contrast, heat does not penetrate deeply into soil or rock; it remains near the surface. Obviously, no
mixing can occur on land because it is not fluid. In-stead, heat must be transferred by the slow process
of Temperature (°C)
–10 1 12 23 34 45 56
0 30 – 4
20 –12 10
–16
Figure 3–3 The data for these four cities reminds us that latitude (Earth–Sun relationship) is a major
control of temperature.
Concept Check 3.2
1 List five controls of temperature other than latitude.
2 Provide two examples that illustrate that latitude is not the only temperature control.
Land and Water
In Chapter 2 you saw that the heating of Earth’s surface con-trols the heating of the air above it.
Therefore, to understand variations in air temperature, we must understand the varia-tions in heating
properties of the different surfacesthat Earth presents to the Sun—soil, water, trees, ice, and so on. Different
land surfaces reflect and absorb varying amounts of incoming solar energy, which in turn cause
variations in the temperature of the air above. The greatest contrast, however, is not between different
land surfaces but between land and water. Figure 3–4 illustrates this idea nicely. This satellite image
shows surface temperatures in portions of Nevada, California, and the adjacent Pacific Ocean on the
afternoon of May 2, 2004, during a spring heat wave. Land-surface temperatures are clearly much
higher than water-surface temperatures. The image shows the extreme high surface tem-peratures in
southern California and Nevada in dark red.*
*Realize that air temperatures are cooler than surface temperatures. For example, the surface of a
sandy beach can be painfully hot even though the temperature of the air above the sand is comfortable.
– 8
JFMAMJJASOND Month
100
NEVADA
CALIFORNIA
PACIFIC OCEAN
14 34 53 73 93 Temperature (°F)
113 133 Figure 3–4 The differential heating of land and water is an important control of air temperatures. In this
satellite image from the afternoon of May 2, 2004, water-surface temperatures in the Pacific Ocean are
much lower than land-surface temperatures in California and Nevada. The narrow band of cool
temperatures
in the center of the image is associated with mountains (the Sierra Nevada). The cooler water
temperatures immediately offshore are associated with the California Current (see Figure 3–9). (NASA)
Temperature ( ̊C)
Temperature ( ̊F)
Chapter 3 Temperature 69
Box 3–1 North America’s Hottest and Coldest Places
Most people living in the United States have experienced temperatures of 38°C (100°F) or more. When
statistics for the 50 states are examined for the past century or longer, we find that every state has a
maximum temperature record of 38°C or higher. Even Alaska has recorded a temperature this high. Its
record was set June 27, 1915, at Fort Yukon, a town along the Arctic Circle in the interior of the state.
Maximum Temperature Records
Surprisingly,the state that ties Alaska for
the “lowest high” is Hawaii. Panala, on the south coast of the big island, recorded 38°C on April 27, 1931.
Although humid tropical
and subtropical places such as Hawaii are known for being warm throughout the year, they seldom
experience maximum tempera-tures that surpass the low to mid-30s Celsius (90s Fahrenheit).
The highest accepted temperature record for the United States as well as the entire Western
Hemisphere is 57°C (134°F). This long-standing record was set at Death Val- ley, California, on July 10,
1913. Summer temperatures at Death Valley are consistently among the highest in the Western Hemisphere.
During June, July, and August, tem- peratures exceeding 49°C (120°F) are to be expected.
Fortunately, Death Valley has few human summertime residents.
heat the ground. In addition, subsiding air that warms by compression as it de-scends is also common to
the region and contributes to its high maximum temperatures.
Minimum Temperature Records
The temperature controls that produce truly frigid temperatures are predictable, and they should come
as no surprise. We should expect extremely cold temperatures during winter in high-latitude places that
lack the moderating influence of the ocean (Figure 3–A). Moreover, stations located on ice sheets and
glaciers should be especially cold, as should stations positioned high in the mountains. All of these
criteria apply to Greenland’s Northice Station (elevation 2307 meters (7567 feet)). Here on Janu- ary 9, 1954, the
temperature plunged to

 

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