1. Chapter 3: Introduction to the
Atmosphere
Image courtesy of cimss.ssec.wisc.edu
McKnight’s Physical Geography:
A Landscape Appreciation,
Tenth Edition, Hess

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Introduction to the Atmosphere
• Size of Earth’s Atmosphere
• Composition of the Atmosphere
• Vertical Structure of the Atmosphere
• Human-Induced Atmospheric Change
• Depletion of the Ozone Layer
• Weather and Climate
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Size of Earth’s Atmosphere
• Atmosphere uniformly
surrounds Earth
• Held down by Earth’s
gravity
• Extends up to 10,000
km from the surface
• More than 50% of the
total mass is below 6 km
3
Figure 3-2

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Composition of the Atmosphere
• Two primary gas types
– Permanent
• Oxygen and Nitrogen
– Variable
• Water Vapor
• Carbon Dioxide
• Ozone
• Permanent gases make
up over 95% of total
atmosphere
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Composition of the Atmosphere
• Particulates
– Non-gaseous particles
which exist in the
atmosphere
– Many human-induced
and natural types
– Many are hygroscopic
– Some reflect or
absorb sunlight
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Figure 3-4

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Vertical Structure of the
Atmosphere
• Thermal Layers
– Troposphere—lowest 10-15
km of atmosphere; most
weather occurs here
– Stratosphere—stagnant air
– Mesosphere—middle of
atmosphere
– Thermosphere—“heat”
– Exosphere—transitions into
interplanetary space
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Figure 3-5

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Vertical Structure of the
Atmosphere
• Air Pressure
– Analogous to the “weight” of
the air
– Decreases with height at
nonconstant rate
– Low-levels compressed by
air above, so surface
pressure is higher
– 90% of atmosphere is in
lowest 16 km
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Figure 3-8

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Vertical Structure of the
Atmosphere
• Composition
– Homosphere—lowest
80 km
– Heterosphere—above
heterosphere
– Ozone layer—between
15 and 48 km;
ozonosphere
– Ionsophere—between
60 and 400 km; source
of auroras
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Figure 3-9

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Human-Induced Atmospheric
Change
• Introduction of impurities into the
atmosphere at rapid pace
• Received international attention in recent
years
• Example is the reduction of ozone by CFCs
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Depletion of the Ozone Layer
• Chemistry of
ozone depletion
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Figure 3-12

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Depletion of the Ozone Layer
• The “Hole” in the
Ozone layer
• Mainly affects polar
regions
• The Montreal Protocol
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Figure 3-13

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Human-Induced Atmospheric
Change
• Definition
• Primary versus
secondary pollutants
• Primary pollutants
– Particulates
– Carbon monoxide
– Nitrogen compounds
– Sulfur compounds
• Secondary pollutants
– Photochemical smog
– Ozone
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Figure 3-15

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Weather and Climate
• Weather—short-term
atmospheric conditions
for a specific area
• Meteorology
• Climate—aggregate
long-term weather
conditions
• Climatology
• Weather versus climate
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Weather and Climate
• Distinction between continental and maritime
climates
• Seattle, WA, and Fargo, ND, have vastly different
climates
• Maritime climates typically much more humid
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Weather and Climate
• General circulation of
the atmosphere
– Semipermanent wind
pattern on Earth
• General circulation of
the oceans
– Oceanic broad-scale
semi-permanent
motions
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Figure 3-17

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Weather and Climate
• Altitude
– Four controls of
weather and climate
affected by altitude
• Topographic barriers
– Can drastically alter
climate due to
orographic change in
wind patterns
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Figure 3-20

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Weather and Climate
• Storms
– Control weather and climate
through atmospheric
modification
– Some storms prominent
enough to affect climate
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Figure 3-21

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Weather and Climate
• Coriolis effect
– Rotation of Earth modifies path of forward motion over
great distances
– Discovered by Gaspard Coriolis
– Causes a rightward turn to motion in the Northern
Hemisphere
– Causes a leftward turn in the Southern Hemisphere
– Deflection greatest at the poles; zero at the equator
– Proportional to the speed of the object
– Has no influence on speed
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Weather and Climate
• Coriolis effect
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Figure 3-22

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Summary
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• Earth’s atmosphere is a shallow “ocean” of air
that uniformly surrounds the Earth
• The atmosphere consists of many permanent
and variable gases
• The gas with the highest concentration in
Earth’s atmosphere is nitrogen (78%)
• The atmosphere has various vertical structures
that describe it
• Five main spheres make up the thermal
atmosphere

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Summary
21
• The homosphere and heterosphere describe the
gas composition of the atmosphere at different
heights
• Most auroral activity occurs in the ionosphere
• Human activity has modified the atmospheric
composition through pollution and ozone
depletion
• Weather and climate, while related, involve
atmospheric conditions on different time scales

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Summary
22
• Many controls exist that modify the four primary
weather elements
• The Coriolis effect is an apparent force that
exists due to the rotation of Earth