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Meteorology Today: An Introduction to Weather, Climate, and The Environment, First Canadian Edition
by C. Donald Ahrens, Peter L. Jackson, Christine E. J. Jackson
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Meteorology today : an
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Earth’s atmosphere: the view from space.
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1
Earth and Its Atmosphere
T
o fly in space is to see the reality of Earth, alone.
To touch the earth after is to see beauty for the
first time.
Roberta Bondar, scientist, neurologist, physician,
Canada’s first female astronaut aboard the Space Shuttle
Discovery Mission, January 22–30, 1992.
The Ukrainian Weekly, Nov. 2, 2003, Volume 71, Number 44, pg. 13.
atmosphere
atmos
atm
e
biosphere
he
ere
anthrosphere
cryosphere
hydrosphere
h
hyd
ydros
re
e
lithosphere
phere
re
CONTENTS
Earth as a System
Overview of Earth’s Atmosphere
4
4
Vertical Structure of the Atmosphere
Weather and Climate
12
19
S
K
ummary
ey Terms
NEL
28
28
3
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4
CH A PTE R 1
O
ur atmosphere is a delicat e, life-g iving blanket of air
that surrounds Earth. In one way or another, it inf uences everything we see and hear—it is intimately connected to our lives. Air is with us from birth. We cannot detach
ourselves from its presence. At Earth’s surface, we can travel for
many thousands of kilomet res (km) in an y hor izontal direction, but should w e move a mer e 8 km abo ve the surfac e, we
would suffocate. We may be able to survive without food for a
few weeks or without water for a few da ys, but without air, we
would not sur vive more than a few min utes. Just as f sh are
conf ned to water, we are conf ned to an ocean of air.
Earth w ithout its at mosphere w ould not ha ve lak es or
oceans. There would be no sounds, no clouds, no c olourful
sunsets. The beautiful pageant ry of the sky w ould be absent.
It would be unimag inably cold at nig ht and unbear ably hot
during the day. Everything on Earth would be at the mercy of
an intense sun beating down on a parched planet.
Living on Earth’s surface, we have adapted so completely
to our airy environment that we sometimes forget how truly
remarkable air is. Even though it is tast eless, odourless, and
invisible, it protects us from the sun’s scorching rays and provides us w ith a mixtur e of gases that allo w life t o f ourish.
Because we usually cannot see, smell, or taste air, it may seem
surprising that between your eyes and the pages of this book
there are trillions of air molecules. Some of them ma y have
been in a cloud yesterday or over another continent last week.
Some may have been par t of a life-g iving br eath for something that li ved h undreds, thousands, or e ven millions of
years ago. Air truly connects everything on Earth.
In this c hapter, we will examine a n umber of important
concepts and ideas about Earth’s atmosphere, many of which
will be expanded on in subsequent chapters. However, we will
start by discussing Ear th as a set of interconnected systems;
the atmosphere is one.
Earth as a System
Earth is made up of several interlinked systems, one of which
is the atmosphere. A system is a set of interacting interrelated
elements forming a complex whole.
Each system can be clearly def ned. Systems interact with
each other, and their parts interact within the system. We will
def ne four major Earth systems, some with subsystems (refer
to the illustration on the chapter opening page):
1. The atmosphere includes the gaseous par t of Earth from
its surface to the exosphere, where the atmosphere gradually merges with space.
2 . The lithosphere (sometimes called the geosphere)
encompasses the solid Earth. It includes all the rock and
geologic material making up the planet. It includes the
soil, whic h is sometimes t reated as a separ ate syst em
called the pedosphere.
3. The hydrosphere includes Earth’s watery parts, both fresh,
salt, and frozen water (i.e., snow and ice). The frozen part
is sometimes treated separately as the cryosphere.
4 . The biosphere encompasses all life on Ear th—plants,
animals, and h umans. We sometimes separ ate ourselves
into a h uman syst em called the anthrosphere, which
encompasses our h uman pr esence in the w orld. I t
includes our economy, culture, technology, communications, structures, and any activities associated with these.
To fully and correctly understand phenomena in natur e,
we mu st holistically consider the int eractions w ithin the
system, as w ell as w ith other en vironmental syst ems. F or
example, understanding Ear th’s c hanging climat e in volves
understanding the climate within the atmospheric system and
its int eraction w ith the hydrosphere thr ough the oc ean
because ocean conditions, especially sea surface temperature,
have a major impact on w eather and climat e. Ov er longer
periods of time, climat e and the at mosphere’s c omposition
are governed by the gas e xchanges of plants in the biosphere
and the w eathering of rocks in the lithosphere. Even considering a single system requires knowledge of the various disciplines that stud y the pr ocesses oc curring in that syst em.
Understanding the at mosphere as a ph ysical system requires
interdisciplinary knowledge.
Chapters in this book descr ibe parts of the at mospheric
system. These ar e connected to other syst ems. We have created a “systems icon” on the opening page of each chapter as
a guide t o illust rate the linkages betw een the syst ems. This
will assist y ou in understanding what syst ems ar e involved
and how they interrelate as you read each chapter.
Overview of Earth’s Atmosphere
The universe contains billions of galaxies, and each galaxy is
made up of billions of stars. Stars are hot, glowing balls of gas
that gener ate energ y b y c onverting h ydrogen int o helium
near their c entres. Our sun is an a verage-sized star situat ed
near the edge of the Milky Way galaxy. Revolving around the
sun are eight planets, including Earth (see ● Figure 1.1),* and
the other mat erial (e.g , c omets, ast eroids, met eors, d warf
planets) that comprise our solar system.
Warmth for our solar system is provided primarily by the
sun’s energ y. At an a verage distanc e of nearly 150 million
kilometres from the sun, Ear th intercepts only a v ery small
fraction of the sun ’s t otal energ y output. A por tion of this
solar radiation† is c onverted int o other for ms of energ y,
warming Ear th and at mosphere, e vaporating wat er, and
driving the at mosphere int o the patt erns of e veryday w ind
and weather we experience. Radiation allows Earth to maintain a global average surface temperature of about 15⬚C. This
seems c omfortable, but because it is a g lobal a verage t emperature, it is composed of widely ranging temperatures from
all parts of the world. Thermometer readings can drop below
*Pluto was previously classif ed as a true ninth planet but recently was reclassif ed
as a planetary object called a dwarf planet.
†
Radiation or radiant energy is energy transferred in the form of waves that have
electrical and mag netic properties. Lig ht that w e see, as w ell as ult raviolet (UV )
light, is radiation. Chapter 2 contains more on this important topic.
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Earth and Its Atmosphere
5
NASA
● F I G U R E 1.1 Relative sizes and positions for planets in our solar syst em. Pluto is
included as an object called a d warf planet.
(Planet positions are not to scale.)
–85⬚C during a fr igid Antarctic night and climb abo ve 50⬚C
during the day in hot subtropical deserts.
Although our atmosphere extends upward for many hundreds of kilometres, almost 99 percent of it lies w ithin 30 km
of Ear th’s surface (see ● Figure 1.2). In fact, if Ear th were to
shrink to the siz e of a bask etball, its inhabitable at mosphere
would be thinner than a piec e of paper. This thin blank et of
air, composed pr imarily of nit rogen and o xygen, constantly
shields Earth’s surface and its inhabitants from the sun’s dangerous ult raviolet r adiant energ y and fr om the onslaug ht of
material from interplanetary space. Nestled in this thin atmosphere are clouds of liquid water and ice crystals that are part
of the g lobal water cycle. There is no def nite upper limit t o
the atmosphere; it just bec omes thinner and thinner, eventually merg ing w ith the empt y spac e that sur rounds all the
objects in our solar system.
NASA
Composition of the Atmosphere Earth’s atmosphere is a
● F I G U R E 1. 2 Earth’s atmosphere as viewed from space. The atmosphere is the thin blue r egion along the edge of Earth.
thin, gaseous en velope c omposed mostly of nitrogen (N 2)
(about 78%) and oxygen ( O2) (about 21%), w ith small t o
trace amounts of other gases, primarily water vapour, argon,
and carbon dioxide (CO 2). Many of the gases in the at mosphere ha ve cy cles of pr oduction (sour ces) and r emoval
(sinks), so the composition of air for several gases is a dynamic
process. The study of the cycling of molecules and n utrients
on Earth is called biogeochemistry because most of the cycles
involve int eraction betw een the biosphere, with the other
Earth systems.
▼ Table 1.1 shows the relative distribution, sources, sinks,
and r esidence times of the var ious per manent and var iable
gases present in a v olume of air near Ear th’s surface. Permanent gases ar e also called c onstant gases because their c oncentrations ar e nearly c onstant thr oughout the at mosphere
and ha ve not c hanged m uch o ver r ecent Ear th hist ory,
whereas variable gases exist in small and variable amounts. As
many of these gases occupy only a small fraction of a percent
in a v olume of air near the surfac e, they are referred to collectively as trace gases. (For a closer look at the c omposition
of air at Ear th’s surfac e, r ead F ocus on a Special T opic: A
Breath of Fresh Air on p. 8.)
The r elative amounts of nit rogen and o xygen ar e fairly
constant in the atmosphere up to an elevation of about 80 km.
At Ear th’s surfac e, ther e is a balanc e betw een dest ruction
(output) and pr oduction (input) of these tw o gases. F or
example, nitrogen is removed from the atmosphere primarily
by biolog ical processes that in volve soil bact eria and b y tiny
ocean-dwelling plankt on that c onvert it int o n utrients that
help fortify the ocean’s food chain. Nitrogen is returned to the
NEL
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6
▼
CH A PTE R 1
Table 1.1 Composition of the Atmosphere near Earth’s Surface
PERMANENT GASES
Parts per
Million*
ppm (by
volume)
Gas
Symbol
Percent Dry
Air (by
volume)
Nitrogen
N2
78.084
780,840
decaying plants and animals
combustion
nitrogen-f xing bacteria in
soil and oceans
lightning
14,000,000
Oxygen
O2
20.946
209,460
photosynthesis
water and nitrous oxide breakdown by ultraviolet radiation
in the stratosphere
plant and animal respiration
decaying plants and animals
chemical rock weathering
growth of shellf sh
4,500
Argon
Ar
0.93
9,300
radioactive decay of
potassium
no sinks
forever, gradually
accumulating
Neon
Ne
0.0018
18
radioactive decay of Earth
materials
no sinks
forever, gradually
accumulating
Helium
He
0.0005
5
radioactive decay of uranium
and thorium
drifts into space
2,000,000
Hydrogen
H2
0.00006
0.6
oxidation of methane
automobile exhaust
volcanoes
drifts into space
6.5
Xenon
Xe
0.000009
0.09
radioactive decay of Earth
materials
no sinks
forever, gradually
accumulating
Symbol
Percent Dry
Air (by
volume)
Parts per
Million*
ppm (by
volume)
Water
vapour
H2O
0 to 4
0 to 40,000
Carbon
dioxide
CO2
0.0389
Methane
CH4
0.00018
Atmospheric Sources
Atmospheric Sinks (removal
mechanism)
Atmospheric
Residence Time †
(in years)
VARIABLE GASES
Gas and
Particles
Atmospheric Sinks (removal
mechanism)
Atmospheric
Residence Time †
(in years)
evaporation
transpiration
precipitation
0.026 or 9.5 days
389
respiration
combustion,
(especially fossil
fuels)
industrial activity
volcanoes
oceans
absorbed by oceans
photosynthesis
burying organic material
(landf lls)
5 to 200 plus,
depending on
source
1.8
wetlands
growing rice
agriculture
ruminant digestion (cattle,
sheep, bison, deer, etc.)
landf ll decay
biomass burning
sewage treatment
termites
ocean bacteria
atmospheric oxidation (breaks 8.4
down when it reacts with
OH (hydroxyl) radicals)
uptake in soils
Atmospheric Sources
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Earth and Its Atmosphere
7
VARIABLE GASES-CONT’D
Symbol
Percent Dry
Air (by
volume)
Parts per
Million*
ppm (by
volume)
Nitrous
oxide
N2O
0.0000314
Ozone
O3
Gas and
Particles
Particles
(dust, soot,
etc.)
Chlorof uorocarbons
CFCs
Atmospheric
Residence Time †
(in years)
Atmospheric Sources
Atmospheric Sinks (removal
mechanism)
0.314
nitrogen breakdown by bacteria
in soils and oceans
agricultural soils and manure
fossil fuel combustion
sewage
destruction through reaction
with ultraviolet radiation
and oxygen in the stratosphere
uptake in soils
120
0.000004
0.04‡
oxygen breakdown by ultraviolet radiation in the stratosphere
photochemical smog
recombines to form oxygen
(O2) in the stratosphere
reacts with vegetation in the
troposphere
0.25 or 91 days
0.000001
0.01–0.15
volcanoes
dust from soil
f res
sea spray
combustion (fossil fuels,
biomass)
removed by rain and settling
by gravity
0 to 0.04 (minutes to 14 days,
depending on size
in the troposphere and longer
in the stratosphere)
production by humans for
refrigerants, propellants, and
solvents
destroyed by ultraviolet radiation in the stratosphere
55 (CFC11)
140 (CFC12)
0.00000002 0.0002
(
)
1
*Parts per million (ppm) measure very small amounts as 1 par t in 1 million par ts ________
. For example, 389 CO 2 parts per million (by volume) means
1,000,000
that there are 389 CO 2 molecules in every 1,000,000 air molecules.
†
Residence time indicates the time that the substanc e remains in the atmosphere.
‡
In the stratosphere (altitudes between 11 and 50 km), values are about 5 to 12 parts per million (ppm).
atmosphere mainly through decaying plant and animal matter.
This conversion and use of nitrogen by the biosphere is critical
to its productivity because nitrogen, in forms other than N2, is
an impor tant macronutrient. Oxygen, on the other hand, is
removed from the at mosphere when organic matt er decays;
when o xygen c ombines w ith other substanc es t o pr oduce
oxides; and dur ing br eathing as lung s tak e in o xygen and
release carbon dioxide (CO 2). Oxygen is added t o the at mosphere dur ing phot osynthesis as plants c ombine car bon
dioxide and wat er to produce sugar and o xygen in the pr esence of sunlight.
Water vapour (H2O) is an invisible gas whose concentration
varies greatly from place to place and fr om time to t ime. Close
to the surfac e in war m, st eamy, t ropical locations, wat er
vapour may account for up to 4 percent of Earth’s atmospheric
gases, wher eas in fr igid polar ar eas, its c oncentration ma y
dwindle to a fraction of a percent (see Table 1.1). Water vapour
molecules are invisible. They become visible only when the y
transform into larger liquid or solid par ticles, such as cloud
droplets and ic e cr ystals, whic h ma y e ventually g row large
enough in size to fall from the sky as rain or snow. The process
of water vapour changing into liquid water is called condensation, whereas the conversion of liquid water to water vapour
is called evaporation. Falling r ain, snow, or some c ombination of these is called precipitation. In the lower atmosphere,
water is everywhere. It is the only substance that exists as a gas,
a liquid, and a solid at t emperatures and pr essures normally
found near Ear th’s surface (see ● Figure 1.3). Water, through
the hydrologic cycle, t ransforms and cir culates betw een the
atmosphere and hydrosphere and is like the lifeblood linking all
of Earth’s systems.
Water vapour is an e xtremely impor tant at mospheric
gas. As it c hanges from gas t o liquid t o ice, it r eleases large
amounts of energ y, called latent heat ; the r everse t ransformations, fr om ic e t o liquid t o gas, r equire the addition of
energy, which is then st ored as lat ent heat. Latent heat is an
important s ource o f at mospheric e nergy, espec ially for stor ms,
such as thunderstorms and hurricanes. Moreover, water vapour
is a potent greenhouse gas because it strongly absorbs a portion
of Earth’s outgoing radiant energy. Thus, water vapour plays a
signif cant role in Earth’s heat–energy balance.
Carbon dioxide (CO 2) gas is a small (about 0.0389 per cent) but impor tant natur ally oc curring c omponent of
Earth’s air. Car bon dio xide ent ers the at mosphere mainly
through decaying vegetation, but it also comes from volcanic
eruptions, e xhaling br eaths of animals, bur ning fossil fuels
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8
CH A PTE R 1
FFOC U S O N A S PE C I A L TO PIC
A Breath of Fresh Air
If we could examine a breath of air, we would
see that air, like everything else, is composed
of atoms. Although we cannot see atoms
individually, they are composed of electrons
whirling about an extremely dense centre.
The centre, or nucleus, contains the atom’s
protons and neutrons. Almost all of the
atom’s mass is concentrated here, in a trillionth of the atom’s entire volume. In the
nucleus, the proton carries a positive charge,
whereas the neutron is electrically neutral.
Each circling electron carries a negative charge.
As long as the total number of protons in
the nucleus equals the number of orbiting
electrons, the atom is balanced and electrically
neutral (see ● Figure 1).
Most air particles are molecules, which
are combinations of two or more atoms
(e.g., nitrogen, N2, and oxygen, O2). Most
molecules are electrically neutral, but a
few are electrically charged as they have
lost or gained some of their electrons.
Charged atoms and molecules are called
ions, and these can react with other atoms
or molecules.
An average breath of fresh air contains a
tremendous number of molecules. With every
deep breath, trillions of molecules from the
atmosphere enter your body. Some of these
inhaled gases become a part of you, whereas
others are exhaled.
The volume of an average-sized breath of
air is about a litre. Near sea level, there are
roughly 10 thousand million, million, million
(1022)* air molecules in a litre. So,
1 breath of air ⬇ 1022 molecules
● F I G U R E 1 An atom has protons and neutrons at
its centre (called a nucleus) with electrons orbiting this
centre. Molecules are combinations of two or more
atoms. The air we breathe is mainly molecular nitrogen
(N2) and molecular oxygen (O2).
We can appreciate the size of this number
when we compare it to the number of stars in
the universe. Astronomers have estimated that
there are about 100 billion (1011) stars in an
average-sized galaxy and that there may be
as many as 1011 galaxies in the universe. To
determine the total number of stars in the
universe, we multiply the number of stars in a
*The notation 1022 means the number one followed by
22 zeroes. For further explanation of this system of
notation (called scientific notation), see Appendix A.
(such as coal, oil, and natural gas), and deforestation. Carbon
dioxide is r emoved from the at mosphere dur ing photosynthesis as plants c onsume CO 2 and t ransform it int o car bon
stored in their roots, branches, and leaves. Oceans act as huge
reservoirs for CO 2 as ph ytoplankton (tin y, dr ifting wat er
plants) f x* CO2 into their organic tissues. Car bon dioxide
that dissol ves dir ectly int o surfac e wat er mix es do wnward
and circulates through greater depths. Estimates are that the
oceans hold mor e than 50 times the t otal atmospheric CO 2
*Carbon f xation is a pr ocess that c onverts CO 2 gas int o solid car bon, usually b y
photosynthesis.
galaxy by the total number of galaxies and
obtain
1011 ⫻ 1011 ⫽ 1022 stars in the universe
Therefore, each breath of air contains
about as many molecules as there are stars in
the known universe.
In Earth’s entire atmosphere, there are
nearly 1044 molecules. To imagine this,
remember that 1044 is 1022 squared and there
are 1022 molecules in a single breath. Consequently, there are about 1022 breaths of air in
the entire atmosphere or
1022 ⫻ 1022 ⫽ 1044 molecules in the
atmosphere
In other words, there are as many molecules in a single breath as there are breaths in
the atmosphere.
Each time we breathe, the molecules we
exhale enter the turbulent atmosphere. If we
wait a long time, those molecules will eventually become thoroughly mixed with all the
other air molecules. If none of the molecules
are consumed in other processes, eventually,
there would be a molecule from that single
breath in every breath that is out there. So,
considering the many breaths people exhale
during their lifetimes, it is possible that our
lungs contain molecules that were once in the
lungs of people who lived hundreds or even
thousands of years ago. In a very real way, we
all share the same atmosphere.
content. ● Figur e 1.4 illust rates impor tant wa ys car bon
dioxide enters and leaves the atmosphere.
● Figure 1.5 reveals that the concentration of atmospheric
CO2 has risen more than 23 per cent since 1958, when it was
f rst measured at the Mauna Loa Observatory in Hawaii. This
increase means that mor e CO 2 is ent ering the at mosphere
than is being removed. The increase appears to be mainly due
to fossil fuel burning; however, deforestation also plays a role
as trees that are cut, burned, or left to rot release CO2 directly
into the air, which also may result in soil CO 2 being released.
Deforestation is thoug ht to account for about 20 per cent of
the obser ved incr ease. CO 2 measur ements for earlier time
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9
© C. Donald Ahrens
Earth and Its Atmosphere
●
F I G U R E 1. 3 Earth’s atmosphere is a rich mixture of many gases,
with clouds of condensed water vapour and ice crystals. Water in gas,
liquid, and solid forms exists here. The ocean’s surface evaporates,
forming invisible water vapour. Rising air currents condense water
vapour into many billions of tiny liquid droplets that appear as puffy
cumulus clouds. When rising air in the cloud e xtends to greater and
colder heights, some of the liquid droplets freeze into minute ice crystals.
periods come from ice cores (see ● Figure 1.6). In Greenland
and Antarctica, tin y bubbles of air t rapped w ithin the ic e
sheets reveal that for several thousand years before the industrial r evolution, CO 2 levels w ere r elatively stable at about
280 par ts per million (ppm), althoug h o ver longer time
periods, CO 2 levels ha ve f uctuated c onsiderably. S ince the
early 1800s, CO 2 levels have increased more than 38 per cent.
With CO 2 levels pr esently incr easing b y about 0.4 per cent
annually (1.9 ppm/y ear), scientists no w estimat e that the
concentration of CO2 will likely rise from its current value of
about 389 ppm in 2010 t o a value near 500 ppm t oward the
end of this century.
Carbon dio xide is another impor tant g reenhouse gas.
Like wat er vapour , it t raps a por tion of Ear th’s outgoing
radiant energy. Consequently, as the at mospheric concentration of CO2 increases, so should the average global surface air
temperature. In fact, in the past c entury, Earth’s average surface temperature has warmed by approximately 0.74⬚C. Mathematical climat e models that pr edict futur e at mospheric
conditions estimat e that if le vels of CO 2 (and other g reenhouse gases) c ontinue at their pr esent rates, Ear th’s air t emperature near the surfac e c ould war m b y an additional 3 ⬚C
by the end of this c entury. As we shall see in Chapt er 16, the
● F I G U R E 1. 4 The main components of the atmospheric carbon
dioxide cycle. The grey lines show processes that put carbon dioxide into
the atmosphere; the red lines show processes that remove carbon dioxide
from the atmosphere.
negative consequences of g lobal war ming, suc h as r ising sea
levels and the rapid melting of polar ice, will be felt worldwide.
Carbon dioxide and water vapour are not the only greenhouse gases. R ecently, others ha ve been gaining not oriety,
primarily because they are becoming more concentrated and
are mor e effecti ve g reenhouse gases than CO 2. S uch gases
include methane (CH 4), nitrous oxide (N2O), and chlorof uorocarbons (CFCs).
Levels of methane (CH 4), for e xample, have been r ising
over the past c entury, increasing recently by about one-half
of 1 per cent per y ear. Most methane appears t o derive from
the br eakdown of plant mat erial b y c ertain bact eria in r ice
paddies, wet oxygen-poor soil, the biolog ical activity of termites, and bioc hemical r eactions in the st omachs of c ows.
Why methane is incr easing so r apidly is cur rently under
study. L evels of nitrous oxide (N 2O), c ommonly kno wn as
laughing gas, have been r ising annually at the r ate of about
one-quarter of a per cent. N itrous o xide for ms in the soil
through a c hemical pr ocess involving bact eria and c ertain
microbes. Ultraviolet light from the sun destroys it.
Chlorof uorocarbons (CFCs) represent a group of greenhouse gases that, up until recently, had been increasing in concentration. At one time, the y w ere the most w idely used
propellants in spray cans and were also used as refrigerants, as
propellants for blowing plastic foam insulation, and as solvents
for cleaning elect ronic microcircuits. Although their a verage
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10
CH A PTE R 1
400
CO2 concentration (ppm)
390
380
370
360
350
340
330
320
310
1958
1968
1978
1988
1998
2008
● F I G U R E 1. 5 Measurements of carbon dioxide (CO 2) in parts per
million (ppm) at Mauna Loa Observatory, Hawaii. Higher readings
occur in winter, when plants die and r elease CO2 to the atmosphere.
Lower readings occur in summer, when more abundant vegetation
absorbs CO2 from the atmosphere. The solid line is the a verage yearly
value. Notice that the concentration of CO2 has increased by more than
23 percent since 1958.
NOAA. Dr. Pieter Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/ccgg/trends/)
concentration in a v olume of air is quit e small (see Table 1.1,
p. 7), they have important effects on our atmosphere. Not only
are the y eff cient g reenhouse gases, the y also pla y a par t in
destroying ozone, a protective gas in the upper atmosphere (or
stratosphere, a region in the atmosphere located between about
11 and 50 km above Earth’s surface). As a result of the recognition of their effect on the st ratospheric o zone la yer in the
1980s, they have been phased out and r eplaced with less damaging hydrochlorof uorocarbons (HCFCs).
●
F I G U R E 1. 6 Carbon dioxide (CO2) values in parts per million
during the past 1000 years from ice cores in Antarctica (blue line)
and from Mauna Loa Observatory in Hawaii (red line).
Data courtesy Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory.
NASA
Year
● F I G U R E 1. 7 The darkest colour represents the area of lowest
ozone concentration, or ozone hole, over the Southern Hemisphere on
September 22, 2004. Notice that the hole is larger than the c ontinent of
Antarctica. A Dobson unit (DU) is the ph ysical thickness of the diffuse
and deep ozone layer if it were concentrated as pure ozone and then
brought to Earth’s surface, where 500 DU equals 5 mm.
At the surfac e, ozone (O 3) is the pr imary ing redient in
photochemical smog, * whic h ir ritates the e yes and thr oat
and damages v egetation. B ut the major ity of at mospheric
ozone (about 97 per cent) is found in the upper at mosphere
or st ratosphere, wher e it for ms natur ally as o xygen at oms
combine w ith oxygen molecules. Here the c oncentration of
ozone averages less than 0.002 percent by volume. This small
quantity is important, however, because it shields plants, animals, and humans from the sun’s harmful ultraviolet rays. It
is ironic that o zone, which damages plant life in a pollut ed
environment, pr ovides a natur al pr otective shield in the
upper atmosphere so that plants on the surfac e may survive.
When CFCs enter the stratosphere, ultraviolet rays break
them apart, and the CFCs release ozone-destroying chlorine.
Because of this effect, o zone c oncentration in the st ratosphere has been decr easing o ver par ts of the N orthern and
Southern hemispheres. The reduction in stratospheric ozone
levels over springtime Antarctica has plummet ed at suc h an
alarming rate that during September and October, there is an
ozone hole over the region. ● Figure 1.7 illustrates the extent
of the ozone hole above Antarctica during September 2004. A
similar situation can oc cur o ver the Arctic dur ing the
Northern Hemisphere’s spring; however, it is normally much
less int ense than in the Antarctic because the e xtreme c old
*Originally, the w ord smog meant the c ombining of smoke and fog . Today, however, the word usually refers to the type of pollution that forms in large cities, such
as Los Angeles, Califor nia, as w ell as T oronto, Ontar io, and Vancouver, B ritish
Columbia. Because this type of smog forms when chemical reactions take place in
the presence of sunlight, it is termed photochemical smog.
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Earth and Its Atmosphere
11
© David Weintraub/Photo Researchers
● F I G U R E 1. 8 Erupting volcanoes
can send tons of particles into the atmosphere, along with vast amounts of water
vapour, carbon dioxide, and sulphur
dioxide.
stratospheric temperatures that enhanc e the o zone dest ruction do not normally occur in the Arctic.
Impurities from both natural and human sources are also
present in the at mosphere: wind picks up dust and soil fr om
Earth’s surface and carries it aloft; small saltwater drops from
ocean wa ves ar e sw ept int o the air (on e vaporating, these
drops leave microscopic salt particles suspended in the atmosphere); smoke from for est f res is oft en car ried hig h abo ve
Earth; and v olcanoes spew man y tonnes of f ne ash par ticles
and gases into the air (see ● Figure 1.8). Many kinds of human
activity, especially combustion in industrial or other setting s,
can directly release par ticles or gases that subsequently c ondense to form particles. Some of these pollutants can be car ried by winds for a long distanc e: for e xample, some organic
pollutants and brominated f ame retardants that are produced
in the middle latitudes can be transported to the Arctic, where
they accumulate, causing health and environmental problems.
Collectively, these tin y solid or liquid suspended par ticles of
various composition are called particulates or aerosols.
Some impurities found in the atmosphere are natural and
can be quit e benef cial. Small, f oating par ticles, for instanc e,
act as surfac es on whic h wat er vapour c ondenses t o for m
clouds. H owever, most h uman-made impur ities (and some
natural ones) are a nuisance, as well as a health hazar d. These
we call pollutants. F or e xample, aut omobile eng ines emit
copious amounts of nitrogen dioxide (NO 2), carbon monoxide (CO), and hydrocarbons. In sunlight, nitrogen dioxide
reacts w ith hydrocarbons and other gases t o produce o zone.
Carbon monoxide is a major pollutant of city air. Colourless
and odourless, this poisonous gas forms during the incomplete
combustion of carbon-containing fuel. Hence, over 75 percent
of carbon monoxide in urban areas comes from road vehicles.
The bur ning of sulph ur-containing fuels (suc h as c oal
and oil) releases the colourless gas sulphur dioxide (SO2) into
the air. When the at mosphere is suff ciently moist, the SO 2
may transform into tiny dilute drops of sulphuric acid. Rain
containing sulph uric acid c orrodes metals and paint ed surfaces and tur ns freshwater lakes acidic. Acid r ain is a major
environmental pr oblem, especially do wnwind fr om major
industrial areas. In addition, high concentrations of SO 2 produce serious respiratory problems in h umans, such as br onchitis and emphysema, and have an adverse effect on plant life.
These gas exchanges between the atmosphere and the biosphere, hydrosphere, and lithosphere, which lead to the current
composition of air, illust rate some of the int erconnections
between systems that characterize Earth. These interconnections also ac count for the de velopment of the at mosphere’s
composition over the course of Earth’s evolution.
The at mosphere that or iginally
surrounded Earth was pr obably much different from the air
we breathe today. Ear th’s f rst atmosphere (some 4.6 billion
years ago) most likely consisted of hydrogen and helium, the
two most abundant gases found in the uni verse, as w ell as
hydrogen compounds, such as methane (CH4) and ammonia
(NH3). Most scientists feel that this early atmosphere escaped
into space from Earth’s hot surface.
A sec ond, mor e dense at mosphere g radually enveloped
the Earth as gases fr om molten rock within Earth’s hot int erior escaped thr ough volcanoes and st eam vents. We assume
that v olcanoes spew ed out the same gases then as the y do
today: mostly water vapour (about 80 percent), carbon dioxide
(about 10 percent), and sulphur dioxide or hydrogen sulphide,
with up to a few per cent nitrogen. These gases (mostly wat er
The Early Atmosphere
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12
CH A PTE R 1
vapour and car bon dioxide) probably created Earth’s second
atmosphere.
As millions of years passed, the c onstant outpouring of
gases from the hot interior, known as outgassing, provided a
rich supply of water vapour, which formed into clouds. Some
of Ear th’s wat er may have or iginated fr om n umerous c ollisions w ith small met eors and disint egrating c omets when
Earth was very young. Rain fell on the Ear th for many thousands of y ears, for ming the r ivers, lak es, and oc eans of the
world. During this time, large amounts of CO2 were dissolved
in the oc eans. Thr ough c hemical and biolog ical pr ocesses,
much of the CO 2 became lock ed up in car bonate sedimentary rocks, such as limestone. With much of the water vapour
already condensed and the c oncentration of CO 2 dwindling,
the atmosphere gradually became rich in N2, which is usually
not chemically active.
It appears that O 2, the sec ond most abundant gas in
today’s at mosphere, pr obably began an e xtremely slo w
increase in concentration as energetic rays from the sun split
water vapour (H2O) into hydrogen and oxygen during a process called photodissociation. The h ydrogen (H 2), being
lighter, pr obably r ose and escaped int o spac e, wher eas the
oxygen r emained in the at mosphere. S imilarly, phot odissociation of CO 2 produced oxygen in the early at mosphere by
splitting into CO and O, which then reacted with OH to produce O2. The concentration of O2 in the early atmosphere was
kept in check, however, by the production of H2 in volcanoes,
which reacts with O2 to remove it.
About 2 to 3 billion years ago, the slow increase in oxygen
may have been enoug h for pr imitive plants t o evolve. Or the
plants may have evolved in an almost o xygen-free (anaerobic)
environment. At any r ate, plant g rowth g reatly enr iched our
atmosphere w ith oxygen. The r eason for this enr ichment is
that, during the process of photosynthesis, plants, in the pr esence of sunlig ht, combine car bon dioxide and wat er to produce oxygen. Of course, as plants r espire and decay, they take
up oxygen and r elease carbon dioxide, reversing this pr ocess.
How, then, do plants r esult in incr eased atmospheric oxygen?
Some plants e ventually become embedded in sediments and
join the lithosphere, becoming fossil fuels and organic sedimentary rocks such as limest one. In this case, they effectively
remove CO 2 and enhanc e O 2 in the at mosphere. Hence, after
plants and the biosphere evolved, the atmospheric oxygen content incr eased mor e r apidly, pr obably r eaching its pr esent
composition about several hundred million years ago.
BR IEF R E V IE W
Before going on to the next several sections, here is a review of
some of the important concepts presented so far:
●
●
Earth’s atmosphere is a mixture of many gases. In a volume of
dry air near the surface, nitrogen (N2) occupies about 78 percent and oxygen (O2) about 21 percent.
Water vapour varies spatially and temporally. It normally occupies less than 4 percent in a volume of air near the surface and
●
●
●
can condense into liquid cloud droplets or transform into delicate ice crystals. Water is the only substance in our atmosphere
that is found naturally as a gas (water vapour), as a liquid
(water), and as a solid (ice).
Both water vapour and carbon dioxide (CO2) are important
greenhouse gases. Some trace gases are also effective greenhouse gases.
Ozone (O3) in the stratosphere protects life from harmful ultraviolet (UV) radiation. At the surface, ozone is a harmful main
ingredient of photochemical smog.
The majority of water on our planet is believed to have come
from Earth’s hot interior through outgassing.
Vertical Structure of the Atmosphere
A vertical prof le in the atmosphere identif es how properties
change w ith altitude. The at mosphere can be v iewed as a
series of layers as one mo ves fr om spac e t o Ear th’s surfac e.
Each layer can be def ned in a number of ways: by the manner
in which air t emperature varies through it, by the gases that
comprise it, or even by its electrical properties. Before we can
examine these various atmospheric layers, we need to understand the vertical prof le of two important variables: air pressure and air density.
A BRIEF LOOK AT AIR PRESSURE AND AIR DENSITY Earlier in this c hapter, we learned that our at mosphere is mor e
crowded close to Earth’s surface. This occurs because air molecules (as w ell as e verything else) ar e held near Ear th b y
gravity. This st rong, invisible for ce pulls e verything t oward
Earth’s centre. In the at mosphere, it squeez es or c ompresses
air molecules closer together, which causes their number in a
given v olume t o incr ease. The mor e air ther e is abo ve any
level in the at mosphere, the mor e w eight, the g reater the
squeezing or compression effect, and the greater the number
of air molecules in a g iven volume.
Consequently, gravity has an effect on the weight of objects,
including air. In fact, weight is the force acting on an object due
to gravity. Weight is def ned as the mass of an object multiplied
by the acceleration of gravity or
weight ⫽ mass ⫻ gravity
An object’s mass is the amount of matter in the object.
The mass of air in a sealed c ontainer is the same e verywhere
in the universe. However, if you were to instantly travel to the
moon, where the ac celeration of gravity is m uch less than it
is on Ear th, the mass of air in that c ontainer w ould be the
same, but its weight would decrease.
The density of an y substanc e, including air , is det ermined by the mass of atoms and molecules that make up the
substance and the amount of space between them. In other
words, densit y t ells us ho w m uch matt er e xists in a g iven
space or volume. We can express density in a variety of ways.
The molecular density of air is the number of molecules in a
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Earth and Its Atmosphere
13
given volume. Most commonly, density is g iven as the mass
of air in a g iven volume or
mass
density ⫽ _______
volume
In the SI syst em of units (see Appendix A), mass is g iven in
kilograms (kg) and v olume is g iven in cubic met res (m 3).
Near sea le vel, air densit y is about 1.2 kilog rams per cubic
metre (1.2 kg m –3).*
There are appreciably more molecules within the samesized v olume of air near Ear th’s surfac e than ther e ar e at
higher levels of the atmosphere. Consequently, air density is
greatest at the surfac e and decr eases as w e move to hig her
altitudes. Notice in ● Figure 1.9 that because air near the
surface is c ompressed, air densit y nor mally decr eases very
rapidly at f rst and then mor e slo wly as w e mo ve far ther
away from the surface. This is an example of an exponential
rate of change. The t erm exponential change descr ibes the
situation when the rate at which a property changes is proportional to the cur rent size of the pr operty. In the case of
air density, it decreases rapidly near the surfac e, where it is
large, and then decr eases less r apidly in the upper at mosphere, where it is smaller.
Air molecules ar e in c onstant motion. On a mild spr ing
day near the surface, an air molecule will collide about 10 billion times eac h second w ith other air molecules. It w ill also
bump against objects ar ound it—houses, t rees, f owers, the
ground, and even people. Each time an air molecule bounc es
against a person, it gives a tiny push. This small push or force
divided by the area on which it pushes is called pressure and
can be written as
force
pressure ⫽ _____
area
In the at mosphere, the pr essure resulting from multiple
molecular “pushes” is sur prisingly large. If we could weigh a
column of air that has a cr oss section of one squar e met re
and extends from sea le vel to the t op of the at mosphere, its
mass w ould be o ver 10,000 kg or 10 met ric t onnes† (see
Figure 1.9). Under nor mal conditions, this r esults in at mospheric pressures near sea level that are close to 101,325 newkg
1 , so kg m⫺3 means __
*The notation “m⫺3” means __
or kilograms per cubic metre.
m3
m3
†
A c ommon misunderstanding oc curs because the e veryday usage of kilograms
confuses the t erms weight and mass and t reats them as thoug h the y ar e the
same. They are not. Here the one squar e metre column extending from sea le vel
to the t op of the at mosphere has a mass of 10,339.3 kg of air. When w orking
with the SI unit syst em, weight is the mass of air (10,339.3 kg) m ultiplied b y
gravity (9.8 m s ⫺2), so w eight is actually measur ed in units of for ce (kg m s ⫺2)
called newtons (N). Thus, the air’s weight ⫽ mass ⫻ g ⫽ 10,339.3 kg ⫻ 9.8 m s –2 ⫽
101,325 kg m s –2 ⫽ 101,325 N.
††
To calculate the pressure for the one square metre column of air extending from
sea level to the top of the atmosphere referred to here, we must f rst compute the
weight of the air column. The air’s weight ⫽ mass ⫻ g ⫽ 10,339.3 kg ⫻ 9.8 m s ⫺2
⫽ 101,325 kg m s ⫺2 ⫽ 101,325 N. Since this weight is distributed over one square
metre, the pressure is 101,325 N m ⫺2, and a new ton per square metre (N m ⫺2) is
a pressure term also known as a pascal (abbreviated as Pa). Hectopascals (1 hPa ⫽
100 Pa) are commonly used units of pressure, as are kilopascals (1 kPa ⫽ 1000 Pa).
● F I G U R E 1. 9 Both air pressure and air density decrease exponentially with increasing altitude. The average mass per square metre of all
the air molecules above Earth’s surface is 10,339.3 kg, which produces
an average pressure of 1,013.25 hPa.
tons per square metre.†† So if more molecules are packed into
the air column, the air becomes more dense, it weighs more,
and the surfac e pressure goes up . On the other hand, when
fewer molecules ar e in the c olumn, the air w eighs less, and
the surface pressure goes do wn. In summary, the surfac e air
pressure can be c hanged by changing the mass of air abo ve
the surface.
Billions of air molecules push constantly on the human
body. This for ce is e xerted equally in all dir ections and is
what we call pressure. We are not crushed by it because billions of molecules inside our bod y push outwar d just as
hard. E ven thoug h w e do not actually feel this c onstant
bombardment of air, we can detect quick changes in it. For
example, if w e climb r apidly in ele vation, our ears ma y
“pop.” This happens because the air c ollisions outside our
eardrums lessen. The popping oc curs as the air c ollisions
between the inside and the outside of our ears equaliz e. A
drop in the n umber of collisions informs us that the pr essure has decreased. The force exerted by air molecules is less
as ther e ar e few er air molecules the hig her y ou ar e abo ve
Earth’s surface. A similar t ype of ear popping oc curs as w e
drop in elevation.
WEATHE R WATCH
Located in the U.S. Rocky Mountains, Denver, Colorado, has an
elevation of 1609 m and a Major League Baseball franchise. The air
density in this “mile-high” city is normally about 15 percent less
than the air density at sea level. Less air density causes less drag
force on a baseball as it moves through the air. A baseball hit in
Denver will travel farther than one hit in a city closer to sea level,
such as Toronto. Consequently, a “hit” that is a home run in
Denver could be an “out” at the SkyDome in Toronto because of
air density.
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14
CH A PTE R 1
FFOC U S O N A S PE C I A L TO PIC
NASA
Earth is unique. Not only does it lie at just the
right distance from the sun so that life as we
know it flourishes, it also provides its inhabitants with an atmosphere rich in nitrogen and
oxygen—two gases that are not abundant in
the atmospheres of Venus or Mars, our closest
planetary neighbours.
The Venusian atmosphere is 95 percent
carbon dioxide with minor amounts of water
vapour and nitrogen. An opaque acid-cloud
deck encircles the planet, hiding its surface.
Measurements reveal a turbulent atmosphere
with twisting eddies and fierce winds in excess
of 200 km hr–1. This thick, dense atmosphere
produces a surface air pressure of about
90,000 hPa, which is 90 times greater than
that on Earth. On Earth, one would have to
descend to a depth of about 900 m in the
ocean to experience a similar pressure. Moreover,
this thick atmosphere of CO2 produces a strong
greenhouse effect, with a scorching hot surface
temperature of 480⬚C.
The atmosphere of Mars, like that of
Venus, is mostly carbon dioxide with small
amounts of other gases. Unlike Venus, the Martian atmosphere is very thin and heat rapidly
escapes from the surface. Surface temperatures
on Mars are much lower, averaging around
–60⬚C. The combination of evidence from the
Martian surface gathered by NASA’s Phoenix
NASA
The Atmospheres of Other Planets
T
● F I G U R E 2 An image of Jupiter extending from
the equator to the southern polar latitudes. The spots,
including the Great Red Spot, are spinning eddies similar
to the storms that exist in Earth’s atmosphere.
● F I G U R E 3 Neptune’s Great Dark Spot. White
wispy clouds below this spot are similar to the high wispy
cirrus clouds we have on Earth. However, on Neptune,
they are probably composed of methane ice crystals.
Mars Lander and the planet’s thin, cold atmosphere, with virtually no cloud cover, currently
has scientists believing that there is no liquid
water on the Martian surface, although ice was
found just under the surface. This thin atmosphere produces an average surface air pressure
of about 7 hPa, which is less than one-hundredth of that experienced at the surface of
Earth. On Earth, similar pressures are observed
at altitudes of nearly 35 km. Occasionally, huge
dust storms develop near the Martian surface.
Such storms may be accompanied by winds of
several hundreds of kilometres per hour. These
winds carry fine dust around the entire planet.
The dust gradually settles out, coating the landscape with a thin, reddish veneer.
The atmosphere of the largest planet,
Jupiter, is much different from that of Venus and
Mars. Jupiter’s atmosphere is mainly hydrogen
(H2) and helium (He), with minor amounts of
methane (CH4) and ammonia (NH3). A prominent feature on Jupiter is the Great Red Spot, a
Air molecules not only tak e up spac e, fr eely dar ting,
twisting, spinning , and c olliding w ith e verything ar ound
them, but as w e have seen, these same molecules also ha ve
weight. In fact, air is surprisingly heavy. The weight of all the
air sur rounding Ear th is a stagger ing 5136 t rillion met ric
tonnes, or about 5.136 ⫻ 10 18 kg . This w eight of air molecules acts as a do wnward force on the Ear th. The amount of
force e xerted o ver an ar ea of surfac e is called atmospheric
pressure or, simply, air pressure.* The pressure at any level in
the atmosphere may be measured in t erms of the total mass
of air per unit area above any point. As we climb in elevation,
fewer air molecules are above us; hence, atmospheric pressure
*Because air pr essure is measur ed w ith an inst rument called a barometer, atmospheric pressure is often referred to as barometric pressure.
always dec reases w ith inc reasing he ight. Lik e air densit y, air
pressure decr eases r apidly at f rst and then mor e slo wly at
higher levels, as illustrated in Figure 1.9.
● Figur e 1.10 also illust rates ho w r apidly air pr essure
decreases with height. Near sea le vel, atmospheric pressure is
usually close to 1000 hPa. Normally, just above sea level, atmospheric pressure decreases by about 10 hPa for every 100-metre
(m) increase in elevation. At higher levels, air pressure decreases
much more slowly with height. Much like air density, air pressure shows an e xponential decrease w ith heig ht. With a sealevel pressure near 1000 hPa, we can see in Figur e 1.10 that at
an altitude of only 5.5 km, the air pressure is about 500 hPa, or
half of the sea-level pressure. This situation means that if you
were at a mer e 5.5 km abo ve Ear th’s surfac e, you w ould be
above one-half of all the molecules in the at mosphere.
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Earth and Its Atmosphere
huge atmospheric storm that measures about
three times larger than Earth. This storm spins
counterclockwise in Jupiter’s southern hemisphere (see ● Figure 2). Large white ovals near
the Great Red Spot are similar smaller storm
systems. Unlike Earth’s weather machine, which
is driven by the sun, Jupiter’s massive swirling
clouds appear to be driven by a collapsing core
▼
of hot hydrogen. Energy from this lower region
rises toward the surface; then it, along with Jupiter’s rapid rotation, stirs the cloud layer into
more or less horizontal bands of various colours.
Swirling storms exist on other planets,
such as Saturn and Neptune. In fact, the large
dark oval on Neptune (see ● Figure 3) appears
to be a storm similar to Jupiter’s Great Red
15
Spot. The white wispy clouds in the photograph are probably composed of methane ice
crystals. Studying the atmospheric behaviour of
other planets may give us added insight into
the workings of our own atmosphere. Additional information about size, surface temperature, and atmospheric composition of our solar
system’s planets is given in ▼ Table 1.
Table 1 Our Solar System: Surface Temperatures and Atmospheric Components
DIAMETER
Kilometres
Sun
Mercury
1392 ⫻ 10
AVERAGE DISTANCE
FROM SUN
AVERAGE SURFACE
TEMPERATURE
Millions of Kilometres
°C
3
MAIN ATMOSPHERIC
COMPONENTS
5505
—
4880
58
260*
—
Venus
12,112
108
480
CO2
Earth
12,742
150
15
N2, O 2
Mars
6800
228
⫺60
CO2
Jupiter
143,000
778
⫺110
H2, He
Saturn
121,000
1427
⫺190
H2, He
Uranus
51800
2869
⫺215
H2, CH4
Neptune
49000
4498
⫺225
N2, CH4
Pluto
3100
5900
⫺235
CH4
*This value is for the side of Mercury that receives sunlight.
At the ele vation of the hig hest mountain peak on Ear th,
Mount Everest (8.850 km), the air pr essure would be about
300 hPa. This summit is abo ve nearly 70 per cent of all the
air molecules in the at mosphere. At an altitude appr oaching
50 km, the air pr essure is about 1 hP a, whic h means that
99.9 percent of all the air molecules ar e below this le vel. Yet
the at mosphere e xtends up wards for man y h undreds of
kilometres, g radually becoming thinner and thinner until it
ultimately merges with outer space. (Up to now, we have concentrated on Earth’s atmosphere. For a brief look at the atmospheres of the other planets, read Focus on a Special Topic: The
Atmospheres of Other Planets on p. 14.)
LAYERS OF THE ATMOSPHERE We have seen that both air
pressure and density decrease exponentially with height above
Earth’s surface. Air temperature,* however, has a mor e complicated vertical prof le.
Look closely at ● Figure 1.11 and notice that air temperature normally decreases from Earth’s surface up to an altitude
of about 11 km. This decr ease in air t emperature w ith
increasing height is primarily due to sunlight warming Earth’s
surface, whic h then war ms the air abo ve the surfac e (see
Chapter 2 for mor e details). The r ate at whic h the air t emperature decreases with height is called the temperature lapse
rate. The average or standard lapse r ate in the lo wer at mosphere is about 6.5 ⬚C for e very 1000 m r ise in ele vation.
*Air temperature is a quantity measured by a thermometer that represents the degree
of hotness or coldness of the air. It is also a measur e of the kinetic energy of the air
molecules, which is proportional to their speed squared, as we will see in Chapter 2.
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16
CH A PTE R 1
WEATHE R WATCH
If you are flying in a jet aircraft at 9000 m above Earth’s surface,
the air temperature outside your window would typically be about
⫺43⬚C. As air temperatures normally decrease with increasing
height, the air temperature outside your window may be more
than 60⬚C colder than air at the ground directly below where you
are flying.
● F I G U R E 1.1 0 Atmospheric pressure decreases rapidly with height.
Climbing to an altitude of only 5.5 km, where the pressure is 500 hPa,
would put you above one-half of the atmosphere’s molecules. Climbers
to the peak of Mount Everest (8850 m above sea level) know this all too
well as breathing becomes so diff cult above 8000 metres above sea level
that the last section of the climb is known as the “death zone.”
Remember that these are average rates, and on any given day,
real temperature lapse rates can differ from the average. Lapse
rates f uctuate day to day and season to season. Occasionally,
air t emperatures actually increase w ith heig ht (so ther e is a
negative lapse rate), creating a temperature inversion.
The atmosphere from the surface up to about 11 km contains all of the w eather w e ar e familiar w ith on Ear th. This
region is kept well stirred by rising and descending air currents.
Here it is c ommon for air molecules t o cir culate through a
depth of more than 10 km in just a few da ys. This r egion of
circulating air extending upward from Earth’s surface to where
the air stops becoming colder with height is called the troposphere—from the Greek tropein, meaning to turn or change.
Notice in Figur e 1.11 that just abo ve 11 km the air t emperature normally stops decreasing with height. Here the lapse
rate is z ero. This r egion, where, on a verage, the air t emperature r emains c onstant w ith heig ht, is r eferred t o as an isothermal (equal t emperature) zone.* The bott om of this z one
marks the top of the troposphere and the beginning of another
atmospheric layer, the stratosphere. The boundary separating
the t roposphere fr om the st ratosphere is called the tropopause. The heig ht of the t ropopause var ies. I t is nor mally
found at hig her ele vations o ver equat orial r egions and
decreases in elevation as we travel poleward. Generally all over
the world, the tropopause occurs at higher altitudes in summer
and at lower ones in w inter. In some regions, the t ropopause
*In many instances, the isother mal layer is not pr esent, and an in version occurs
where the air temperature begins to increase with increasing height.
“breaks” and is diff cult t o locat e, and her e scientists ha ve
observed t ropospheric air mixing w ith st ratospheric air and
vice versa. These breaks also mark the position of jet streams—
high-altitude winds that meander in a nar row channel, like a
river, often at speeds exceeding 100 knots (185 km h –1).*
From Figure 1.11, we can see that, in the stratosphere, the
air temperature begins to increase w ith heig ht, producing a
temperature inversion. The in version region, along w ith the
lower isothermal layer, tends to keep the vertical air currents
of the troposphere from spreading into the stratosphere. The
inversion also tends to reduce the amount of vertical motion
in the st ratosphere, making the st ratosphere a st ratif ed,
stable layer.
Even thoug h air t emperature incr eases w ith heig ht, the
air at an altitude of 30 km is e xtremely cold, averaging less
than –46 ⬚C. Above polar latitudes, at this altitude, air t emperatures can change dramatically from one week to the next.
A sudden warming can raise the temperature in one w eek by
more than 50 ⬚C. (Such a r apid war ming, althoug h not w ell
understood, is pr obably due t o sinking air associat ed w ith
circulation changes that oc cur in lat e winter or early spr ing,
as well as with the poleward displacement of strong jet stream
winds in the lower stratosphere.)
How do w e measure the at mosphere’s temperature prof le? Radiosondes, or weather balloons, are instruments that
measure the air’s vertical temperature prof le up to elevations
exceeding 30 km. See F ocus on an O bservation: The Radiosonde on p. 18 for more information about them.
The r eason for the in version in the st ratosphere is that
ozone gas, whic h is c oncentrated in the upper at mosphere,
plays a major role in heating the air at this altitude. Recall that
ozone is important because of its protective capacity to absorb
energetic ultraviolet solar energy. Some of this absorbed energy
warms the stratosphere, which explains why there is an in version. If ozone were not pr esent, the air w ould probably continue to become colder with height, as it does in theroposphere.
t
Figure 1.11 represents the average temperature prof le for
Earth’s middle latitudes. Notice that the le vel of maxim um
ozone concentration is obser ved near 25 km, yet the st ratospheric air temperature reaches a maximum near 50 km. This
occurs because o zone absor bs only c ertain wa velengths of
*A knot is a nautical mile per hour . A nautical mile was or iginally def ned as a
minute of latitude (1/60th of a deg ree of latitude). Although not an SI unit, the
knot is a c ommon measure for wind speed used in aviation, boating, and meteorology. One knot is equal t o 1.852 kilomet res per hour (km hr ⫺1) or 0.51 met res
per second (m s ⫺1).
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Earth and Its Atmosphere
F I G U R E 1.1 1 Thermal layers of the atmosphere as def ned by the
average air temperature prof le (heavy line) above Earth’s surface.
●
ultraviolet r adiation fr om the sun. E ven thoug h ther e ar e
fewer o zone molecules, m uch of the energ y r esponsible for
heating the stratosphere is absorbed in the upper par t of this
layer and removed before it reaches the lower layers containing
the o zone maxim um. So e ven thoug h ther e is mor e o zone
lower down, there is not much radiation left at the right wavelengths to be absorbed, and the heating is less.Also, the low air
density and the la yer’s st ratif cation mak e the t ransfer of
energy from the upper to the lower stratosphere quite slow.
Above the st ratosphere is the mesosphere or middle
sphere. The boundar y near 50 km separ ates these layers and
is called the stratopause. At this level, the stratosphere reaches
its hig hest t emperature. H ere air is e xtremely thin and air
pressure is quit e lo w, a veraging about 1 hP a, whic h means
that only one-thousandth of all the at mosphere’s molecules
occurs above this le vel and 99.9 per cent of the at mosphere’s
mass is located below it.
The per centage of nit rogen and o xygen in the mesosphere is about the same as it is at sea le vel, but the air’s low
density mak es it impossible t o get enoug h oxygen, and w e
would suffocat e in a matt er of min utes w ithout the pr oper
breathing equipment. Being adapted to living nearer sea level,
our brains soon become oxygen starved—a condition known
as hypoxia. High-elevation mountaineers and pilots who f y
above 3 km for t oo long without an oxygen-breathing apparatus experience this. The f rst sy mptoms of hypoxia usually
17
involve no pain, just a feeling of e xhaustion. Soon v isual
impairment sets in, and routine tasks become diff cult. Some
people dr ift int o an inc oherent stat e, neither r ealizing nor
caring what is happening t o them. If this o xygen def ciency
persists, a person will lapse into unconsciousness and death.
Suffocating is not the only pr oblem that would be experienced in the mesospher e. Exposur e t o ult raviolet solar
energy w ould cause se vere bur ns on e xposed bod y par ts.
Also, g iven the lo w air pr essure, the blood in one ’s v eins
would begin to boil at normal body temperatures.
The air t emperature in the mesospher e decr eases w ith
height, partly because there is little o zone in the air t o absorb
solar r adiation. Consequently, the molecules near the t op of
the mesosphere absorb less energy than those near the bottom
of the layer. This results in decreasing temperature with height.
So we f nd air in the mesosphere becoming colder with height
up to an elevation near 85 km. At this altitude, the temperature
of the atmosphere reaches its lowest average value of ⫺90⬚C.
The “hot layer” above the mesosphere is the thermosphere.
The boundar y that separ ates the lo wer, c older mesospher e
from the hig her temperature ther mosphere is the mesopause.
In the ther mosphere, oxygen molecules absor b energetic solar
rays, increasing the kinetic energy of the molecules and therefore the t emperature.* Because ther e are very few at oms and
molecules in the ther mosphere, the absor ption of a small
amount of solar energ y can cause a large incr ease in kinetic
energy and ther efore air t emperature. Furthermore, because
the amount of solar energ y affecting this r egion depends
strongly on solar acti vity, temperatures in the ther mosphere
vary from day to day (see ● Figure 1.12). The low density of the
thermosphere also means that an air molecule w ill move an
average distance of over one kilomet re before colliding w ith
another molecule. A similar air molecule at Earth’s surface will
move an a verage distanc e of less than one-millionth of a
centimetre before it collides with another molecule. Because of
this, it would not feel“warm” in the thermosphere, even though
the temperature might be quite high. This is because our per ception of air’s “warmth” has to do with both the average speed
of molecules c olliding w ith our bod y (i.e., the t emperature)
and the n umber of molecules c olliding with our bod y. In the
thermosphere, molecules are zipping around quickly, but there
are t oo few of them t o impar t m uch heat, so it w ould feel
extremely c old. M oreover, it is in the ther mosphere wher e
charged par ticles from the sun int eract w ith air molecules t o
produce dazzling aur ora or nor thern lig hts displays. We w ill
investigate aurora in Chapter 2.
Air densit y in the upper ther mosphere is so lo w that air
temperatures in this region are not measured directly. They are
determined by observing the orbital change of satellites caused
by the drag of the atmosphere. Even though the air is extremely
thin, enoug h air molecules st rike a sat ellite to slow it do wn,
making it drop into a slightly lower orbit. This is the reason the
*As w ill be discussed in Chapt er 2, air t emperature is actually a measur e of the
kinetic energ y of the molecules in air . In other w ords, it r epresents how fast the
molecules are moving about.
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18
CH A PTE R 1
FFOC U S O N A N O B S E RVAT IO N
The Radiosonde
T
*A radiosonde that is dropped by parachute from an
aircraft is called a dropsonde.
complement radiosondes by using instruments
that measure radiant energy to provide vertical
temperature profiles in inaccessible regions.
When winds are added, the device is called a
rawinsonde, although the term radiosonde is
often used generically to include all such instruments. When plotted on a graph, the vertical
distribution of temperature, humidity, and wind
is called a sounding. Eventually, the balloon
bursts—usually somewhere near 33 km altitude
for helium balloons—and the radiosonde
returns to Earth.
Selected weather stations tasked with
releasing radiosondes, called upper-air stations,
release them twice a day, usually at the time
that corresponds to midnight and noon in
Greenwich, England.* Releasing radiosondes
is an expensive operation because the instruments are never retrieved, and even when spent
ones are found, they are usually so damaged
that they are not reusable. Modern satellites
*Since weather is global, it is important to standardize
weather observations around a standard time. Coordinated Universal Time (UTC) is used. UTC is very similar
to Greenwich Mean Time (GMT), corresponding to the
local solar time at Greenwich, near London, England.
Sometimes UTC is abbreviated as Z; so UTC time is
also called “Zulu” time. Appendix F on p. A-18 gives
conversions between North American local standard
times and UTC.
Solar Maximum Mission spacecraft fell t o Earth in Dec ember
1989, and the Russian space station Mir did the same in March
2001. The amount of drag is r elated to the densit y of the air ,
and the densit y is r elated t o the t emperature. So , b y det ermining air densit y, scientists ar e able t o construct a v ertical
prof le of air temperature through the entire atmosphere.
At the t op of the ther mosphere, about 500 km abo ve
Earth’s surface, molecules can move distances of 10 km before
they collide w ith other molecules. Here many of the lig hter,
faster moving molecules t raveling in the r ight direction actually escape Ear th’s gravitational pull. The r egion where atoms
and molecules can shoot off int o spac e is r eferred t o as the
exosphere, and it represents the upper limit of our atmosphere.
So far, w e have e xamined the at mospheric layers based
on the v ertical pr of le of t emperature. However, the at mosphere ma y also be di vided int o la yers based on c hemical
composition. The c omposition of the at mosphere beg ins
to slo wly c hange in the lo wer par t of the ther mosphere.
Below the ther mosphere, the c omposition of air r emains
© C. Jackson
Up to an altitude of about 30 km, the vertical
distribution of temperature, pressure, and
humidity can be obtained using a measuring
device called a radiosonde.* The radiosonde is a
small, lightweight box equipped with electronic
weather sensors, a battery, an antenna, and a
radio transmitter. It is attached to a tightly tied
helium or hydrogen gas-filled balloon by a cord
(see ● Figure 4). Some radiosondes also have a
parachute. As the balloon rises, the attached
radiosonde measures air temperature with a
small electrical thermometer, called a thermistor,
located outside the box. The radiosonde measures humidity electrically by sending an electric
current across a carbon-coated plate. Air pressure is obtained by a small barometer located
inside the box. Every second, all of this information is transmitted to the surface by radio,
where it is processed and stored every two seconds. Some units use special equipment such
as a Global Positioning System (GPS) or weather
radar to track the radiosonde’s position as it
moves through the sky. These types of radiosondes also provide a vertical profile of winds.
● F I G U R E 4 A radiosonde and balloon. Canada’s
upper-air radiosonde network consists of 31 stations
where weather balloons are launched twice daily.
fairly uniform at 78 percent nitrogen, 21 percent oxygen due
to turbulent mixing. When classifying layers chemically, this
lower, well-mixed region is kno wn as the homosphere (see
Figure 1.12). In the ther mosphere, collisions between atoms
and molecules ar e infrequent, and the air is unable t o keep
itself stirred. As a result, diffusion takes over as heavier atoms
and molecules (such as oxygen and nitrogen) tend to settle to
the bott om of the la yer, wher eas lig hter gases (suc h as
hydrogen and helium) f oat t o the t op. The r egion fr om
approximately the base of the thermosphere to the top of the
atmosphere is also called the heterosphere.
THE IONOSPHERE The ionosphere is not r eally a la yer but
rather an electrif ed region within the upper atmosphere where
fairly large concentrations of ions and free electrons exist. Ions
are atoms and molecules that have lost or gained one or mor e
electrons. Atoms lose electrons and become positively charged
when they cannot absorb all of the energy transferred to them
by a colliding energetic particle or the sun’s energy.
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Earth and Its Atmosphere
19
into the ionosphere, into the E and F regions, where the waves
are r ef ected back t o Ear th. C onsequently, at nig ht, ther e is
little absorption of radio waves in the hig her reaches of the
ionosphere and AM radio waves bounce repeatedly from the
ionosphere to the Earth’s surface and back to the ionosphere
again. In this way, standard AM radio waves are able to travel
for many hundreds of kilometres at night.
Around sunr ise and sunset, AM r adio stations usually
make “necessary t echnical adjust ments” t o c ompensate for
the changing electrical characteristics of the D region. Because
they can broadcast over a greater distance at night, most AM
stations reduce their output near sunset. This reduction prevents two stations—both transmitting at the same frequency
but h undreds of kilomet res apar t—from int erfering w ith
each other’ s r adio pr ograms. At sunr ise, as the D re gion
intensif es, the po wer supplied t o AM r adio t ransmitters is
normally increased. FM stations do not need t o make these
adjustments because FM r adio wa ves ar e shor ter than AM
waves and ar e able t o penet rate thr ough the ionospher e
without being ref ected.
F I G U R E 1.1 2 The various layers and regions of the atmosphere:
layers based on temperature are represented by the red line (an active
sun is associated with larger numbers of solar eruptions.), layers based
on chemical composition are shown by the green line, and regions where
electrical properties occur are represented by the dark blue line.
●
The ionosphere usually starts about 60 km above Earth’s
surface and extends to the outer limits of the atmosphere. As
illustrated in Figure 1.12, the bulk of the ionosphere is in the
thermosphere.
The ionosphere plays a major role in AM radio communications, as sho wn in ● Figure 1.13. The lo wer par t of the
ionosphere, called the D re gion, re f ects standard AM r adio
waves back to Earth, but at the same time,it seriously weakens
them thr ough absor ption. At nig ht, the D region gra dually
disappears and AM radio waves are able t o penetrate higher
BR IEF R E V IE W
We have examined our atmosphere from a vertical perspective.
The main points are as follows:
●
●
●
●
●
●
Atmospheric pressure at any level represents the total mass of
air above that level, and atmospheric pressure always decreases
with increasing height above the surface.
The rate at which the air temperature decreases with height is
called the lapse rate. A measured increase in air temperature
with height is called an inversion.
The atmosphere may be divided into layers according to its vertical profile of temperature and its gaseous composition. The
atmosphere can also be divided into regions based on its electrical properties.
The atmospheric layer with the highest temperature is the thermosphere; the layer with the coldest temperature is the mesosphere. Ozone gas is found in the stratosphere.
We live at the bottom of the troposphere, which is an atmospheric layer where the air temperature normally decreases with
height. The troposphere is a region that contains all of the
weather we are familiar with.
The ionosphere is an electrified region of the upper atmosphere
that normally extends from about 60 km to the top of the
atmosphere.
Weather and Climate
●
F I G U R E 1.1 3 At night, the higher region of the ionosphere, the
F region, strongly ref ects AM radio waves, allowing them to be sent over
great distances. During the day, the lower D region strongly absorbs and
weakens AM radio waves, preventing them from being picked up by
distantreceivers.
We w ill now tur n our att ention to weather e vents that tak e
place in the lower atmosphere. The remainder of this chapter
serves as a broad overview of material in later chapters. Many
of the concepts and ideas you will encounter here are designed
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20
CH A PTE R 1
to familiarize you with items you might read about in newspapers or magazines or see on t elevision.
Meteorology is the study of the atmosphere and its phenomena. When w e talk about the weather, w e ar e talking
about the condition of the atmosphere at any particular time
and place. Weather is always changing. It is composed of the
following:
1. air te mperature—the deg ree of hot ness or c oldness of
the air, whic h c orresponds t o the kinetic energ y of air
molecules
2. air pressure—the force of the air above an area
3. humidity—a measure of the amount of water vapour in
the air
4. clouds—visible masses of tiny water droplets and/or ic e
crystals that are above Earth’s surface
5. precipitation—any form of water, either liquid (r ain) or
solid (sno w), that falls fr om clouds and r eaches the
ground
6. wind—the horizontal movement of air
7. visibility—the g reatest distanc e one can see t o identify
prominent objects
If we measure and obser ve these weather ele ments ove r a
specif ed interval of time, say, for many years, we would obtain
the “average weather” of a par ticular area. In addition, if we
keep t rack of the var iability in eac h weather element, we can
def ne the climate of that ar ea. Climate, therefore, represents
the accumulation of daily and seasonal weather events and their
variability, including extreme weather events such as heat waves
in summer and cold spells in winter over a long period of time.
If we were able to watch Earth for thousands to millions
of years, even the climat e would change. We might see h uge
glaciers, r ivers of ic e mo ving do wn st ream-cut valle ys, and
continental sheets of mo ving sno w and ic e spr eading o ver
large portions of North America. Over a time span of about
two million y ears, w e mig ht see m ultiple g laciations wher e
the ice advances and retreats several times. Of course, for this
to happen, the average temperature of North America would
have to decrease and then rise in a cyclic manner.
If we could photograph Earth once every thousand years,
for many hundreds of millions of years we could watch Earth
in time-lapse photography. This would show that climate and
Earth itself are changing: mountains would form and rise up,
only to be torn down by erosion; isolated puffs of smoke and
steam w ould appear as v olcanoes spew hot gases and f ne
dust int o the at mosphere; and Ear th’s entir e surfac e w ould
undergo a g radual t ransformation as c ertain oc ean basins
widen and others shrink.*
In summar y, Ear th is c omposed of a n umber of
dynamic systems, the atmosphere, hydrosphere, lithosphere,
*The movement of Earth’s continents and oc ean f oor is e xplained by the theor y
of plate tectonics. In this theory, Earth’s surface is composed of about eight major
plates that mo ve in r elation to each other. Plate tectonics explains how the lithosphere evolves, how volcanoes and earthquakes occur, how and where mountains,
build, and accounts for the changing distribution of land and ocean surfaces over
geologic time. These changes have greatly affected Earth’s climate.
and biosphere. These are constantly changing and impacting
each other. Whereas major transformations of Earth’s lithosphere ar e c ompleted only aft er long spans of time, the
state of the atmosphere can change in a matter of minutes.
METEOROLOGY: A BRIEF HISTORY The term meteorology
goes back to the Greek philosopher Aristotle, who wrote a book
on natural philosophy entitled Meteorologica in about 340 b.c.
This work represented the sum of knowledge on w eather and
climate at that time, as w ell as mat erial on ast ronomy, geography, and c hemistry. Some of the t opics c overed included
clouds, rain, snow, wind, hail, thunder, and hurricanes. In those
days, anything seen in the air and all substanc es that fell fr om
the sky were called meteors. The term meteorology comes from
the Greek word meteoros, meaning “high in the air.”
In Meteorologica, Aristotle att empted t o e xplain at mospheric phenomena in a philosophical and speculative manner.
Even though many of his speculations were found to be erroneous, Aristotle’s ideas were accepted without reservation for
almost 2000 years. In fact, the bir th of meteorology as a genuine natural science did not tak e place until the in vention of
weather instruments (the thermometer at the end of the 16th
century, the bar ometer for measur ing air pr essure in 1643,
and the hygrometer for measuring humidity in the late 1700s).
As mor e and bett er inst ruments w ere de veloped in the
1800s, the science of meteorology progressed. The invention
of the telegraph in 1843 allowed for the transmission of routine w eather obser vations. The understanding of the c oncepts of wind f ow and storm movement became clearer, and
in 1869, cr ude w eather maps w ith lines of equal pr essure
(isobars) w ere dr awn. Around 1920, the c oncepts of air
masses and weather fronts were formulated in Norway. By the
1940s, daily upper -air balloon obser vations of temperature,
humidity, and pressure gave a three-dimensional view of the
atmosphere, and hig h-f ying militar y aircraft discovered the
existence of jet streams.
Meteorology took another step forward in the 1950s, when
high-speed computers were developed to solve mathematical
equations. At the same time, a group of scientists in Princeton,
New J ersey, de veloped n umerical means for pr edicting the
weather. Prior to this advance, the mathematical equations that
represent the atmosphere had to be simplif ed to by solved “by
hand,” w ith less ac curate r esults. Today, c omputers plot the
observations, draw the lines on the map, and forecast the state
of the atmosphere at some desired time in the future.
After World War II, surplus military radars became available, and many were transformed into precipitation-measuring
tools. I n the mid-1990s, these w ere r eplaced b y the mor e
sophisticated Doppler r adars, whic h ha ve the abilit y t o use
radio waves t o image st orms, their w inds, and pr ecipitation
(see ● Figure 1.14).
In 1960, the f rst weather satellite, TIROS I, was launched,
ushering in space-age meteorology. Subsequent satellites provided a wide range of useful information, ranging from timelapse images of clouds and st orms t o images that depict
swirling ribbons of water vapour f owing around the g lobe.
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21
NOAA
Earth and Its Atmosphere
● F I G U R E 1.1 4 Radar image showing the heavy rain (yellow areas) from thunderstorms embedded in Hurricane Katrina as it
makes landfall near New Orleans on August 29, 2005, at 09:48 UTC. The circular “hole” in the precipitation that is just offshore is
the hurricane eye.
Throughout the 1990s and int o the 21st c entury, sophisticated satellites have supplied c omputers w ith an impr essive
range of imager y and measur ements that suppor t w eather
tracking and forecasts.
equator is 0 ⬚, whereas the latitude of the North Pole is 90 ⬚N
and that of the South P ole is 90 ⬚S. The latitudes betw een
30⬚N and 60⬚N are commonly referred to as the middle latitudes or mid-latitudes.
A SATELLITE’S VIEW OF THE WEATHER A good view of the
weather can be seen fr om a w eather satellite. ● Figure 1.15 is a
satellite image centred over the North American continent taken
in the infrared band such that cold clouds are coloured white in
the image. The image was obtained by combining imagery from
two geostationary satellites situat ed about 36,000 km abo ve
Earth—one located over the western part of the continent and
the other o ver the east ern par t. At this ele vation, the sat ellite
travels at the same rate as Earth spins, which allows it to remain
positioned above the same spot on Earth so that it can continuously monitor what is taking place beneath it.
The solid white grid lines running from north to south on
the satellite image ar e called meridians, or lines of longitude.
Since the z ero mer idian (or pr ime mer idian) r uns thr ough
Greenwich, Eng land, the longitude of any plac e on Ear th is
simply how far east or w est, in deg rees, it is fr om the pr ime
meridian. M ost of N orth America lies betw een 52 ⬚W and
130⬚W longitude.
The solid whit e lines that par allel the equat or are called
parallels of latitude. The latitude of any place is how far north
or south, in degrees, it is from the equator. The latitude of the
Storms of All Sizes Infrared sat ellite images suc h as
Figure 1.15 provide a snapshot related to temperatures in the
atmosphere and on Ear th. The clouds appear whit e because
they are colder than the ground below them, and cold objects
are assigned a white colour in this type of image. Organized
cloud masses ar e st orms. S uperimposed on the sat ellite
image are areas of low pressure called “lows” that correspond
to st orm c entres (indicat ed b y large r ed “L” sy mbols) and
their adjoining weather fronts in red and blue. These middlelatitude cyclonic st orms ha ve w inds spinning about their
centre. In the case of the system over the Great Lakes, there
are two centres (Ls): one over western Lake Superior and the
other over Lake Huron. Another middle-latitude cy clone is
over British Columbia, and a third one is crossing the Maritime pr ovinces. F ronts ar e discussed in Chapt er 11 and
middle-latitude cyclones in Chapter 12.
A smaller but mor e vigorous storm, called a hurricane,
occurs o ver t ropical oc eans (see Figur e 1.14). These st orms
have diameters of a few hundred kilometres and often have a
zone of clear skies at their c entre, called the eye. Near the
surface, in the e ye, w inds are lig ht, skies ar e gener ally clear,
NEL
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22
CH A PTE R 1
F I G U R E 1.1 5 This
satellite image (taken in the
infrared) shows a variety of
cloud patterns and storms
in Earth’s atmosphere on
September 28, 2009, at 12:00
UTC. Clouds are colder than
the ground and are coloured
white in the image. The
coloured base map and
weather fronts are added
after the image is taken.
●
H
H
L
L
L
Lake Superior
L
Lake
Huron
Lake
Michigan
L
Lake Ontario
Environment Canada. Data courtesy of NOAA (2010).
H
L
Ottawa
A Look at a Weather Map We can obtain a better picture
of the middle-latitude st orm by examining a simplif ed surface weather map (see ● Figure 1.17) for the same time as the
Figure 1.15 satellite image. In Figure 1.17, the red letter “L”’s
on the map indicat e r egions of lo w at mospheric pr essure,
called lows, or cyclones, which mark the c entre of the midlatitude st orm. The blue lett er “H”’s on the map r epresent
© C. Donald Ahrens
and the atmospheric pressure is lowest. Around the eye, however, is an extensive region where heavy rain and high surface
winds are reaching peak gusts of 100 knots (185 km h –1). To
be categorized as a h urricane, surface winds must exceed 64
knots* or 119 km h –1. Hurricanes ar e discussed fur ther in
Chapter 15.
Trailing from the Maritimes’ storm system in Figure 1.15
is a line of smaller st orms off Flor ida’s Atlantic c oast. This
line of cloud r epresents clusters of towering cumulus clouds
that ha ve de veloped int o thunderstorms, one of the most
common types of storms. ● Figure 1.16 is an e xample of the
tall, c hurning cum ulonimbus clouds that ar e ac companied
by lig htning, th under, st rong gust y w inds, and hea vy r ain.
Thunderstorms, at their most int ense, can spa wn the most
violent disturbance in the atmosphere, a tornado.
A tornado or twister is an intense, rotating column of air
that e xtends do wnward fr om the base of a se vere th understorm. Tornadoes can appear as ropes or large cylinders. The
majority are less than a kilometre wide, and many are smaller
than a football f eld. Tornado w inds can e xceed 200 knots
(370 km h–1), but most peak at less than 125 knots (232 km h–1).
Some r apidly r otating clouds, called funnel clouds, that
appear to hang fr om the base of a par ent cloud ne ver reach
the ground to form a tornado.
F I G U R E 1.1 6 Thunderstorms developing and advancing along an
approaching cold front.
●
*1 knot ⫽ 1.852 km hr ⫺1 or 0.51 m s ⫺1.
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Earth and Its Atmosphere
H
2
● F I G U R E 1.1 7 Simplif ed
surface weather map taken at the
same time as the satellite image
shown in Figure 1.15. The numbers
on the map represent air temperatures in ⬚C.
–3
H
23
–2
3
L
L
9
2
9
13
7
L
4
H
11
Environment Canada. Data courtesy of NOAA (2010).
Lake
Superior
5
L
Lake
Michigan
Ottawa
L
L.
Huron
L
L.
Ontario
12
13
17
18
regions of hig h pressure, called highs, o r anticyclones. The
circle symbols on the map represent either individual weather
stations or cities wher e obser vations are taken. Wind is the
horizontal mo vement of air and has both dir ection and
speed. Wind dir ection is def ned as the dir ection that the
wind is blo wing from.* On w eather maps, wind direction is
shown by the shaft lines that point toward the weather station
symbol. Wind speed is indicat ed b y the siz e and n umber
of barbs on the w ind-direction shafts. Eac h bar b r epresents
10 knots (18.5 km h –1 or 5.1 m s –1).
Notice how the wind blows around the highs and the lows.
The hor izontal pressure differences create a for ce that star ts
the air mo ving from hig her pressure t oward lower pressure.
The winds are slowed down near Earth’s surface because of its
roughness, or friction. Because of Ear th’s rotation, the w inds
are def ected from their path toward the right in the Northern
Hemisphere.† This def ection, combined with friction due t o
Earth’s surface, causes the winds to blow clockwise and outward
from the c entre of hig hs and counterclockwise and inward
toward the centre of lows.
Also notice by comparing Figures 1.15 and 1.17 that in
the regions of high pressure, skies ar e generally clear. As the
surface air f ows outward away from the centre of a high, air
sinking fr om abo ve m ust r eplace the lat erally spr eading
*For example, if you are facing nor th and the w ind is blo wing in y our face, the
wind is called a “north wind.”
†
This def ecting force, known as the Coriolis force, is discussed more completely in
Chapter 8, as are the winds.
surface air. Since sinking air does not usually produce clouds,
we f nd generally clear skies and fair w eather associated with
the regions of high atmospheric pressure.
The swirling air around areas of high and low pressure is
the major weather producer for the middle latitudes. Look at
the middle-latitude st orm and the surfac e t emperatures in
Figure 1.17 and notic e that t o the southeast of the st orm
affecting the G reat Lakes, southerly w inds from the G ulf of
Mexico are bringing warm, humid air northward over much
of the southeastern portion of the continent. On the st orm’s
western side, c ool, dr y, nor therly br eezes c ombine w ith
sinking air to create generally clear weather over the Prairies
and U.S. Rocky Mountains. The boundary that separates the
warm and c ool air appears as hea vy, c oloured lines on the
map—fronts, across whic h there is a shar p c hange in t emperature, humidity, and wind direction.
Where the cool air from Canada replaces the warmer air
from the Gulf of Mexico, a cold front is drawn in blue, with
arrowheads sho wing the fr ont’s gener al dir ection of mo vement. Where the warm Gulf air is r eplacing cooler air to the
WEATHE R WATCH
When it rains, it rains pennies from heaven—sometimes. On July
17, 1940, a tornado reportedly picked up a treasure of over 1000
16th century silver coins, carried them into a thunderstorm, and
then dropped them on the village of Meschery in the Gorki region
of Russia.
NEL
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
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24
CH A PTE R 1
north, a warm front is drawn in red, with half circles showing
its general direction of movement. Where the cold front has
caught up t o the war m fr ont and c old air is no w r eplacing
cool air , an occluded fr ont, whic h in Canada is called a
TROugh of Warm A ir ALoft (abbr eviated TR OWAL), is
drawn w ith blue and r ed hook sy mbols. Along eac h of the
fronts, warm air is rising, producing clouds and precipitation.
Notice in the sat ellite image (see Figur e 1.15) that the
TROWAL (occluded front) and the c old front appear as an
elongated, curling cloud band that st retches fr om the lo wpressure areas over lakes Superior and Huron into the state of
Pennsylvania south of Lake Erie.
In Figure 1.17, observe the frontal system over southern
Ontario. As the westerly winds aloft push the front eastward,
a person on the outskir ts of Otta wa mig ht obser ve the
approaching fr ont as g radually incr easing and lo wering
clouds, eventually followed by the start of precipitation. On a
Doppler radar image, the advancing precipitation is shown in
● Figure 1.18, which is taken some 15 hours after the weather
map and sat ellite image in Figur es 1.15 and 1.17. As the
system passes thr ough Ottawa, it should e xperience periods
of r ain or sho wers. All of this, however, should g ive way to
clearing skies and surfac e winds from the w est or nor thwest
after the front has moved on.
WEATHER AND CLIMATE IN OUR LIVES Weather and climate pla y a major r ole in our li ves. Weather, for e xample,
often dictates the t ype of clothing w e wear, whereas climate
inf uences the t ype of clothing w e bu y. Climat e det ermines
when t o plant cr ops as w ell as what t ypes of cr ops can be
planted. Weather determines if these same crops will grow to
maturity.
Even when w e ar e pr operly dr essed for the w eather,
wind, humidity, and precipitation change our perception of
how cold or war m it feels. On a c old, windy day, the effects
of wind chill tell us that it feels much colder than it really is,
and if not pr operly dressed, we run the r isk of frostbite or
even hypothermia. On a hot, humid day, we nor mally feel
uncomfortably war m and blame it on the h umidity. I f w e
become too warm, our bodies overheat, and heat exhaustion
or heat stroke may result. Those most lik ely to suffer these
maladies ar e the elderly w ith impair ed cir culatory syst ems
and infants, whose heat r egulatory mechanisms are not y et
fully developed.
Weather affects how we feel in other wa ys, too. Arthritic
pain is most lik ely to occur when r ising humidity is ac companied b y falling pr essures. The incidenc e of hear t attacks
shows a statistical peak aft er the passage of war m fr onts,
when r ain and w ind ar e c ommon, and aft er the passage of
cold fr onts, when an abr upt c hange takes plac e as sho wery
precipitation is ac companied b y c old, gust y w inds. H eadaches ar e c ommon on da ys when w e ar e for ced t o squint,
often due to hazy skies or a thin, bright, overcast layer of high
clouds. F or some people, a war m, dr y w ind blo wing
downslope (for e xample, a chinook w ind in souther n
Alberta) adversely affects their behaviour (they often become
irritable and depr essed). J ust ho w and wh y these w inds
impact h umans physiologically is not w ell underst ood. We
will, ho wever, take up the question of why these w inds ar e
warm and dry in Chapter 9.
When the weather turns colder or war mer than nor mal,
it impacts dir ectly on the li ves and pock etbooks of man y
people. F or e xample, the e xceptionally war m w inter of
1997–98 o ver N orth America sa ved o ver $6.7 billion in
heating costs in the U nited States, whereas Canadian homes
saved an average of $200 each. The exceptional warmth (2 to
8⬚C above normal) in the w inter of 1997–98 was due t o the
effects of a particularly strong El Niño that year. El Niño is a
Environment Canada. Canadian Weather Radar. © Her Majesty The Queen in Right of Canada,
Environment Canada, 2009.
●
F I G U R E 1.1 8
Radar image showing the
light rain associated with
passing of a low-pressure
system and TROWAL over
Ontario on September 29,
2009, at 11:30 p.m. EDT.
The image is a composite
from 10 radars. The
colours denote the intensity of rainfall.
NEL
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Earth and Its Atmosphere
CP PHOTO/Jacques Boissinot
phenomenon discussed in Chapt er 10 that affects g lobal
weather patt erns and ar ises when war mer than nor mal sea
surface t emperatures for m in the east ern t ropical P acif c
Ocean. On the other side of the coin, the colder than normal
winter of 2000–01 over much of North America sent heating
costs soaring as the demand for heating fuel escalat ed.
Major c old spells ac companied b y hea vy sno w and ic e
can play havoc by snarling c ommuter t raff c, cur tailing airport services, closing sc hools, and do wning power lines (see
● Figure 1.19). For example, a huge ice storm during January
1998, affecting east ern Ontar io thr ough souther n Quebec
and Nova Scotia, as well as the northern New England states,
left millions of people without power for as long as a month
and caused o ver $3 billion in damage in Canada, making it
Canada’s costliest natural disaster. When frigid air settles into
the U.S. Deep South, many millions of dollars worth of temperature-sensitive fr uits and v egetables ma y be r uined, the
eventual c onsequence being hig her pr oduce pr ices in the
supermarket. Winter w eather does not ha ve t o be c old t o
cause damage. When fr ontal syst ems st retch fr om the subtropics and cr oss the N orth American West Coast, the y can
bring moist, warm winds and copious amounts of rain with
F I G U R E 1.1 9 The ice storm of 1998 that affected southern
Quebec, eastern Ontario, New Brunswick, and Nova Scotia was Canada’s
costliest natural disaster, at a cost of over $3 billion. About 1.5 million
customers were without electricity for up to 30 days when the weight of
the ice crumpled transmission towers.
●
25
snow over the hig her mountains. These “pineapple express”
storms can result in severe f ooding and loss of electricity due
to downed power lines.
Prolonged dr y spells, especially when ac companied b y
high temperatures, can lead to a shortage of food and, in some
places, w idespread star vation. Parts of Africa, for e xample,
have per iodically suffer ed thr ough major dr oughts and
famine. During the years from 1999 through 2004, the Canadian Prairies experienced the worst prolonged drought in over
100 years, whic h had de vastating impacts on ag riculture. I n
2002 alone, this c ost the Canadian ec onomy $3.6 billion and
some 41,000 jobs.
When the climat e turns hot and dr y, animals suffer t oo.
In 1986, over 500,000 c hickens per ished in the U .S. state of
Georgia dur ing a tw o-day per iod at the peak of a summer
heat wave. Severe drought also has an effect on water reserves,
often forcing communities to ration water and restrict its use.
During per iods of e xtended dr ought, v egetation oft en
becomes tinder-dry, and spar ked b y lig htning or a car eless
human, such a dried-up region can quickly become a raging
inferno. Dur ing 2002, in the midst of the pr airie dr ought,
Alberta e xperienced a f vefold incr ease in the n umber of
wildf res.
Every summer , sc orching heat wa ves tak e man y li ves.
During the past 20 years, an annual average of more than 300
deaths in North America is attributed to excessive heat exposure. Europe suffered through a devastating heat wave during
the summer of 2003, when it is estimat ed that 70,000 people
died, including 14,802 during one two-week period in France
alone. The high death tolls mainly affected the elderly, many
of whom w ere in understaffed car e facilities in the cities
during the t raditional August holiday period. This left them
without support resources that might have helped them cope
with these unusual conditions. Daily maximum temperatures
across the r egion e xceeded 35 t o 40 ⬚C in man y par ts of
Europe, and se veral all-time maxim um temperature records
were set.
Every y ear, the v iolent side of w eather inf uences the
lives of millions. I t is amazing ho w man y people whose
family r oots ar e in the U .S. M idwest kno w the st ory of
someone who was se verely injur ed or killed b y a t ornado.
Tornadoes ha ve not only tak en man y li ves, but, ann ually,
they also cause damage t o building s and pr operty totalling
in the h undreds of millions of dollars as a sing le large t ornado can level an entire section of a town (see ● Figure 1.20).
Although not as fr equent as in the U .S. Midwest, tornadoes
in Canada can also ha ve sig nif cant impacts: in the 1980s,
tornadoes in Barrie, Ontario, and Edmonton, Alberta, killed
35 people.
Although the gentle rains of a typical summer thunderstorm are welcome over much of North America, the heavy
downpours, high winds, and hail of severe thunderstorms
are not. Cloudbursts from slowly moving, intense thunderstorms can pr ovide t oo m uch r ain t oo quickly , cr eating
f ash f oods as small st reams bec ome r aging r ivers c omposed of mud and sand entangled with uprooted plants and
NEL
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CH A PTE R 1
© Eric Nguyen/Corbis
26
● F I G U R E 1. 2 0 A tornado and a rainbow form over south-central
Kansas during June 2004. White streaks in the sky are descending
hailstones.
trees (see ● Figur e 1.21). On a verage, f ooding and f ash
f ooding cause more property damage in Canada and mor e
deaths in the U nited States than any other natur al disaster.
Strong do wndrafts or iginating inside an int ense th understorm (a downburst) cr eate tur bulent w inds that ar e
capable of dest roying crops and inf icting damage on sur face structures. Several airline cr ashes have been att ributed
to the tur bulent wind shear z one w ithin the do wnburst.
Annually, hail damages crops worth millions of dollars, and
lightning takes the lives of about se ven people each year in
Canada and 62 in the U nited Stat es. F orty-f ve percent of
the 8000 a verage annual wildf res in Canada ar e started by
lightning, which causes 81percent of the t otal area burned.
Each y ear, w ildf res dest roy betw een 0.7 and 7.6 million
hectares and directly cost $500 million to $1 billion to control, for a total annual average cost of about $14 billion (see
● Figure 1.22).
Even the quiet side of w eather has its inf uence. When
winds die do wn and h umid air bec omes more tranquil, fog
may for m. Dense fog can r estrict v isibility o ver the wat er,
affecting shipping, and at air ports, causing f ight delays and
cancellations. Every w inter, deadly, fog-r elated aut omobile
accidents oc cur along our busy hig hways. B ut fog has a
positive side, too, especially during a dr y spell, as fog moisture collects on tree branches and drips to the ground, where
it provides water for the root system.
Weather and climate have become so much a part of our
lives that the f rst thing man y of us do in the mor ning is
listen t o the local w eather for ecast. F or this r eason, man y
radio and t elevision newscasts ha ve their o wn “weather-
CP PHOTO/Tom Hanson
● F I G U R E 1. 2 1 Flooding
in Winnipeg during April and
May 1997. The Red River
reached its highest levels since
1826, causing widespread
f ooding affecting southern
Manitoba as well as North
Dakota and Minnesota.
NEL
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Earth and Its Atmosphere
27
FFO C U S O N A S PE C IAL TO PI C
What Is a Meteorologist?
W
● F I G U R E 5 A model that
simulates a three-dimensional
view of the atmosphere. This
computer model predicts how
winds and clouds over North
America will change with time.
NCAR/UCAR/NSF
Most people associate the term “meteorologist”
with the weatherperson they see on television or
hear on the radio. Many television and radio
weathercasters are, in fact, professional meteorologists, but some are not. A professional meteorologist is usually considered to be a person who
has completed the requirements for a university
degree in meteorology or atmospheric science.
This individual has strong, fundamental knowledge concerning how the atmosphere behaves,
along with a substantial background of coursework in mathematics, physics, chemistry, and
the environmental sciences.
A meteorologist uses scientific principles
to explain and to forecast atmospheric phenomena. About two-thirds of the approximately
1350 meteorologists and atmospheric scientists
in Canada (about half of the 9000 in the
United States) work doing weather forecasting
for the Meteorological Service of Canada (the
National Weather Service in the United States).
The rest work for the military or television or
radio stations, work in research, teach atmospheric science courses in colleges and universities, or do meteorological consulting work.
Scientists who do atmospheric research
may be investigating how the climate is
changing, how snowflakes form, or how pollution impacts the environment. Aided by supercomputers, some research meteorologists
simulate the atmosphere using computer
models, to see how it behaves (see ● Figure 5).
Researchers often work closely with scientists
from other fields, such as biologists, environmental scientists, chemists, physicists, oceanographers, and mathematicians, as well as
planners and social scientists, to determine how
the atmosphere interacts with the entire ecosystem. Scientists doing work in physical meteorology may study how radiant energy warms
the atmosphere; those at work in the field of
dynamic meteorology might be using the mathematical equations that describe airflow to learn
more about jet streams. Scientists working in
operational meteorology might be preparing a
weather forecast by analyzing upper-air information over North America. A climatologist, or climate scientist, might be studying the interaction
of the atmosphere and ocean to see what influence such an interchange might have on Earth
many years from now. Consulting meteorologists might be conducting air pollution dispersion modelling to understand the impact of an
industrial facility on air quality.
person” to present weather information and g ive daily forecasts. M ore and mor e of these people ar e pr ofessionally
trained in met eorology, and man y stations r equire that the
weathercaster obtain endorsement from the Canadian Meteorological and Oceanographic Society (CMOS) (or a seal of
approval fr om the American M eteorological Societ y). To
make their w eather pr esentation as up-t o-the-minute as
possible, most stations in Canada tak e ad vantage of the
Meteorologists also provide a variety of
services not only to the general public in the
form of weather forecasts but also to city
planners, contractors, farmers, and large corporations. Meteorologists working for private
weather firms create the forecasts and
graphics that are found in newspapers, on
television, and on the Internet. Overall, there
are many exciting jobs that fall under the
heading of “meteorologist”—too many to
mention here. However, for more information
on this topic, try some of the following
websites:
● http://www.cmos.ca/
● http://www.msc-smc.ec.gc.ca/jobs_emplois/
Careers/Meteorologist_e.cfm
● http://www.ametsoc.org/ and click on
“Students”
information pr ovided b y the M eteorological Ser vice of
Canada (MSC), suc h as c omputerized w eather for ecasts,
time-lapse sat ellite images, and c olour Doppler r adar displays. (A t this point, it is int eresting t o not e that man y
viewers belie ve that the w eatherperson the y see on TV is a
meteorologist and that all met eorologists for ecast the
weather. If you are interested in learning what a met eorologist or atmospheric scientist is and what he or she mig ht do
NEL
Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
Licensed to: CengageBrain User
28
CH A PTE R 1
WEATHE R WATCH
© Jon Hicks/CORBIS
During late August and September 2005, Hurricane Katrina
slammed into Mississippi and Louisiana (see Figure 1.14). In the
city of New Orleans, several levees (that protected the city from
flooding) broke, and flood waters over six metres deep inundated
parts of the city, killing over 1200 people.
● F I G U R E 1. 2 2 Estimates are that lightning strikes Earth about
100 times every second. About 25 million lightning strikes hit the
United States each year, and there are about 2.7 million in Canada.
Consequently, lightning is a very common, and sometimes deadly,
weather phenomenon.
for a living [other than forecast the weather], read Focus on
a Special Topic: What Is a Meteorologist? on p. 27.)
For man y y ears, a staff of t rained pr ofessionals at the
“Weather N etwork”/“Météo Média ” in Canada and “The
Weather Channel” in the United States have provided weather
information 24 hours a da y on cable t elevision. As well, the
Meteorological Ser vice of Canada oper ates Weatheradio
Canada, a national netw ork broadcasting weather and en vironmental infor mation 24 hours a da y on the VHF band
directly from Environment Canada’s Storm Prediction Centres. A special war ning t one can be issued when a w eather
warning is made, which will activate a weather radio’s internal
alert syst em t o tur n on the r adio. A similar syst em called
NOAA Weather Radio exists in the United States.
SUMMARY
This c hapter pr ovided an o verview of Ear th’s at mosphere.
Most of the topics touched on, such as the various storms and
weather syst ems, w ill be e xamined in m uch mor e depth in
subsequent chapters. We saw that the atmosphere is one of a
set of int erconnected syst ems that mak e up Ear th: at mosphere, biospher e/anthrosphere, h ydrosphere/cryosphere,
and lithosphere. Each of these systems is linked to each of the
others in various ways, and these linkages will be highlighted
at the start of each chapter.
Our at mosphere is one r ich in nit rogen and o xygen as
well as smaller amounts of other gases, such as water vapour,
carbon dioxide, and other greenhouse gases whose increasing
levels are resulting in g lobal warming. We examined Earth’s
early atmosphere and found it to be much different from the
air we breathe today.
We investigated the various layers of the atmosphere: the
troposphere (the lowest layer), where almost all weather events
occur, and the st ratosphere, where ozone protects us fr om a
portion of the sun ’s harmful rays. In the st ratosphere, ozone
has decr eased in c oncentration o ver polar r egions dur ing
spring, especially in the Souther n hemispher e. Above the
stratosphere lies the mesospher e, where the air t emperature
drops dramatically with height. Above the mesosphere lies the
thermosphere, where temperatures are highest. At the t op of
the thermosphere is the e xosphere, where collisions between
gas molecules and at oms are so infr equent that fast-mo ving
lighter molecules can actually escape Earth’s gravitational pull
and shoot off into space. The ionosphere represents that portion of the upper at mosphere wher e large n umbers of ions
and free electrons exist.
We looked brief y at the weather map and a satellite image
and obser ved that dispersed thr oughout the at mosphere are
storms and clouds of all siz es and shapes. The mo vement,
intensif cation, and w eakening of these syst ems, as w ell as the
dynamic nature of air itself, produce a variety of weather events
that we described in terms of weather elements. The sum total
of weather and its extremes over a long period of time is what
we call climat e. Although sudden c hanges in w eather ma y
occur in a moment, climatic change takes place gradually over
many years. The study of the atmosphere and all of its related
phenomena is called meteorology, a t erm whose or igin dates
back to the days of Aristotle. Finally, we discussed some of the
many ways weather and climate inf uence our lives.
KEY TERMS
The follo wing t erms ar e list ed (w ith page n umbers) in the
order they appear in the t ext. Def ne each. Doing so w ill aid
you in reviewing the material covered in this chapter.
atmosphere, 4
lithosphere, 4
geosphere, 4
pedosphere, 4
NEL
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
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Earth and Its Atmosphere
hydrosphere, 4
cryosphere, 4
biosphere, 4
anthrosphere, 4
radiation, 4
radiant energy, 4
nitrogen (N2), 5
oxygen (O2), 5
water vapour, 5
argon, 5
carbon dioxide (CO2), 5
trace gases, 5
condensation, 7
evaporation, 7
precipitation, 7
hydrologic cycle, 7
latent heat, 7
photosynthesis, 7
methane (CH4), 9
nitrous oxide (N2O), 9
chlorof uorocarbons
(CFCs), 9
ozone (O3), 10
photochemical smog, 10
ozone hole, 10
aerosols, 11
pollutants, 11
nitrogen dioxide (NO2), 11
carbon monoxide (CO), 11
hydrocarbons, 11
sulphur dioxide (SO2), 11
acid rain, 11
outgassing, 11
photodissociation, 12
density, 12
exponential rate of change, 13
pressure, 13
air pressure, 14
lapse rate, 15
temperature inversion, 16
troposphere, 16
stratosphere, 16
tropopause, 16
radiosondes, 16
mesosphere, 17
thermosphere, 17
kinetic energy, 17
exosphere, 18
homosphere, 19
heterosphere, 19
ionosphere, 19
weather, 20
climate, 20
plate tectonics, 20
meteorology, 20
middle latitudes, 21
middle-latitude cyclonic
storm, 21
hurricane, 21
thunderstorms, 22
tornado, 22
lows, 23
cyclones, 23
highs, 23
anticyclones, 23
wind, 23
wind direction, 23
fronts, 23
cold front, 23
warm front, 24
occluded front, 24
wind chill, 24
frostbite, 24
hypothermia, 24
heat stroke, 24
chinook wind, 24
severe thunderstorms, 25
f ash f oods, 25
downburst, 26
wind shear, 26
QUESTIONS FOR REVIEW
1. What is the pr imary source of energ y for Ear th’s atmosphere?
2. List the four most abundant gases in t oday’s at mosphere.
3. Of the four most abundant gases in our at mosphere,
which one sho ws the g reatest var iation at Ear th’s
surface?
4. What are some of the important roles that water plays in
our atmosphere?
5. Brief y explain the production and natural destruction of
carbon dioxide near Earth’s surface. Give two reasons for
the increase of carbon dioxide over the past 100 years.
29
6. List the tw o most abundant g reenhouse gases in Ear th’s
atmosphere. What makes them greenhouse gases?
7. Explain ho w the at mosphere “protects” inhabitants at
Earth’s surface.
8. What are some of the aerosols in our atmosphere?
9. How has the composition of Earth’s atmosphere changed
over time? Brief y outline the e volution of Earth’s atmosphere.
10. (a) Explain the concept of air pressure in terms of mass
of air above some level.
(b) Why does air pressure always decrease with increasing
height above the surface?
11. What is standar d at mospheric pr essure at sea le vel in
(a) millimetres of mer cury, (b) hect opascals, and
(c) kilopascals?
12. What is the average or standard temperature lapse rate in
the troposphere?
13. B rief y descr ibe ho w the air t emperature c hanges fr om
Earth’s surface to the lower thermosphere.
14. On the basis of temperature, list the la yers of the at mosphere from the lowest to the highest layer.
15. What atmospheric layer contains all of our weather?
16. (a) In what at mospheric la yer do w e f nd the lo west
average air temperature?
(b) The highest average temperature?
(c) The highest concentration of ozone?
17. Above what r egion(s) of the w orld w ould y ou f nd an
ozone hole?
18. How does the ionospher e affect AM radio transmission
during the day versus during the night?
19. Even though the actual c oncentration of oxygen is close
to 21 per cent (b y v olume) in the upper st ratosphere,
explain wh y, w ithout pr oper br eathing appar atus, y ou
would not be able to survive there.
20. Def ne meteorology and discuss the or igin of this word.
21. When someone sa ys that “the w ind dir ection t oday is
south,” does this mean that the w ind is blo wing toward
the south or from the south?
22. Describe some of the featur es obser ved on a surfac e
weather map.
23. Explain ho w w ind blo ws ar ound lo w-pressure ar eas in
the Northern Hemisphere.
24. How are fronts def ned?
25. Rank the following storms in size from largest to smallest:
hurricane, t ornado, middle-latitude cy clonic st orm,
thunderstorm.
26. Weather in the middle latitudes t ends t o mo ve in what
general direction?
27. How does weather differ from climate?
28. Describe some of the ways weather and climate inf uence
the lives of people.
NEL
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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
30
CH A PTE R 1
QUESTIONS FOR THOUGHT
1. Which of the following statements relate more to weather
and which relate more to climate?
(a) The summers here are warm and humid.
(b) Cumulus clouds presently cover the entire sky.
(c) Our lowest temperature last winter was ⫺29⬚C.
(d) The air temperature outside is 22⬚C.
(e) December is our foggiest month.
(f) The hig hest t emperature e ver r ecorded in M idale,
Saskatchewan, was 45.0⬚C on July 5, 1937.
(g) Snow is falling at the r ate of 5 cm per hour.
(h) The average temperature for the month of January in
Edmonton, Alberta, is ⫺13.5⬚C.
2. A standar d pr essure of 1013.25 hect opascals is also
known as one atmosphere (1 ATM).
(a) Look at Figure 1.10 and determine at approximately
what levels you would record a pressure of 0.5 ATM
and 0.1 ATM.
(b) T he s urface air pr essure on M ars is about 0.007
ATM. If you were standing on M ars, the surface air
pressure would be equivalent to a pressure observed
at appr oximately what ele vation in Ear th’s at mosphere?
3. If y ou w ere suddenly plac ed at an altitude of 100 km
above Earth, would you expect your stomach to expand
or contract? Explain.
PROBLEMS AND EXERCISES
1. Keep track of the w eather. On an outline map of North
America, mark the daily position of fronts and pr essure
systems for a per iod of se veral w eeks or mor e. ( This
information can be obtained fr om newspapers, the television news, or the Internet.) Plot the general upper-level
f ow patt ern on the map . O bserve how the surfac e systems mo ve. Relate this infor mation t o the mat erial on
wind, fronts, and cyclones covered in later chapters.
2. Compose a one-w eek journal, including daily newspaper
weather maps and w eather forecasts from the newspaper
or from the Internet. Provide a commentary for each day
regarding the coincidence of actual and predicted weather.
3. Formulate a short-term climatology for your city for one
month b y r ecording maxim um and minim um
temperatures and pr ecipitation amounts e very da y.
You can get this infor mation fr om t elevision, newspapers, the Internet, or your own measurements. Compare
this data t o the actual climat ology for that month. How
can you explain any large differences between the two?
NEL
Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.