Chapter 3: Introduction to the Atmosphere

Image courtesy of cimss.ssec.wisc.edu

Importance of Earth’s Atmosphere

• Provides oxygen• Weather (short-term) & Climate (long-term)• Protection from

UV radiation & meteors

• Temperature Control

• Water (hydrologic cycle)

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

Figure 3-2

Composition of the Atmosphere

• Two primary gas types– Permanent

• Oxygen & Nitrogen• Neither plays a major role in

atmospheric processes– Variable

• Water Vapor• Carbon Dioxide• Ozone• Play significant role in weather &

climate

• Permanent gases make up over 95% of total atmosphere

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• Amount of water vapor in the atmosphere varies from 0-4%

• Water vapor transports heat & regulates temperature

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

0 10 20 30 40 50Precipitable Water (kg/m2)

Water Vapor in the Atmosphere

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• Carbon dioxide also regulates temperature

• Amount of atmospheric CO2 is about 0.039%, but it’s rising– Greenhouse Effect

Carbon Dioxide in the Atmosphere

Composition of the Atmosphere

• Particulates– Non-gaseous particles which exist in the atmosphere– Human-induced & natural types– Some are hygroscopic– Some reflect

or absorb sunlight

Figure 3-4

Vertical Structure of the Atmosphere

• Thermal Layers (temp. alternates from one layer to the next)

• “Sphere” = entire layer• “Pause” = upper boundary of a layer

– Troposphere—lowest layer; weather occurs here; tropopause

• Thickest at Equator & thinnest at Poles due to the Earth’s rotation & convection

– Stratosphere—stagnant air; ozone layer; stratopause

– Mesosphere—middle of atmosphere; meteors burn up; mesopause

– Thermosphere—“heat”– Exosphere—transitions into space

Figure 3-5

Vertical Structure of

the Atmosphere

• Air Pressure– “Weight” of the air– Decreases with height

at non-constant rate– Low-levels compressed

by air above, so surface pressure is higher

– 90% of atmosphere is in lowest 16 km

Figures 3-7 & 3-8

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Measuring Atmospheric Pressure

Vertical Structure of the Atmosphere

• Composition– Homosphere—

uniformly mixed– Heterosphere—

layered– Ozonophere—AKA

ozone layer; high concentration of O3

– Ionsophere—electrically charged ions; source of auroras

Figure 3-9

• Natural Ozone (O3)– Naturally produced by UV radiation to shield us from UV radiation

• Introduction of impurities into the atmosphere at rapid pace• Received international attention in recent years

Figure 3-11

Depletion of the Ozone Layer

Depletion of the Ozone Layer

• Chemistry of Ozone Layer depletion– Reduction/destruction of ozone

by CFCs• The “Hole” in the Ozone layer• Mainly affects polar regions

Figure 3-12Figure 3-13

Human-Induced Atmospheric Change

• Primary vs. secondary pollutants

• Primary pollutants– Particulates– Carbon monoxide– Nitrogen compounds– Sulfur compounds

• Secondary pollutants– Photochemical smog– Ozone

Figure 3-15: Santiago, Chile Smog

Los Angeles, CA Smog

Weather and Climate

• Weather—short-term atmospheric conditions for a specific area– Meteorology

• Climate—aggregate long-term weather conditions– Climatology

• Weather vs. climate

• Latitude is the most important/significant control of weather and climate– Heat received across Earth’s surface from sunlight is a

function of latitude

Weather & Climate: Latitude

Figure 3-16

Weather & Climate: Distribution of Land & Water

• Distinction between maritime & continental climates– Dallas, TX, & San Diego, CA,

have very different climates– Maritime climates = humid

Continental climates = dry• N. (Land) Hemisphere vs. S.

(Water) Hemisphere

Figure 4-24

Weather & Climate: General Circulation of the Atmopshere &

Oceans• General circulation of

the atmosphere– Semipermanent wind

pattern on Earth– Varies with latitude

• General circulation of the oceans– Oceanic broad-scale

semi-permanent motions

– Help transfer heat Figure 3-17

Weather & Climate: Altitude & Topography

• Altitude– All 4 controls of

weather and climate affected by altitude

• Topographic barriers– Can drastically alter

climate due to orographic change in wind patterns

– Windward side vs. Leeward side

Figure 3-20

Weather & Climate: Storms

• Storms– Control weather & climate through atmospheric modification – Some storms are prominent enough to affect climate

Figure 3-21

Weather and Climate

• Coriolis effect– Rotation of Earth modifies path of forward motion of free-

moving objects over great distances– Curves to the right in the N Hemisphere– Curves to the left in the S Hemisphere– Deflection greatest at the poles; zero at the equator– Proportional to

speed of the object– Only influences

direction of an object; no influence on speed of an object

Weather and Climate

• Coriolis effectFigure 3-22

Summary

• 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• 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• 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