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

Water Vapor in the Atmosphere Amount of water vapor in the atmosphere varies from 0-4% Water vapor transports heat & regulates temperature

Carbon Dioxide in the Atmosphere Carbon dioxide also regulates temperature Amount of atmospheric CO2 is about 0.039%, but it’s rising Greenhouse Effect

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

Measuring Atmospheric Pressure

Vertical Structure of the Atmosphere Figure 3-9 Composition Homosphere—uniformly mixed Heterosphere—layered Ozonophere—AKA ozone layer; high concentration of O3 Ionsophere—electrically charged ions; source of auroras

Depletion of the Ozone Layer 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 Chemistry of Ozone Layer depletion Reduction/destruction of ozone by CFCs The “Hole” in the Ozone layer Mainly affects polar regions Figure 3-13 Figure 3-12

Human-Induced Atmospheric Change Figure 3-15: Santiago, Chile Smog Primary vs. secondary pollutants Primary pollutants Particulates Carbon monoxide Nitrogen compounds Sulfur compounds Secondary pollutants Photochemical smog Ozone 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

Weather & Climate: Latitude Latitude is the most important/significant control of weather and climate Heat received across Earth’s surface from sunlight is a function of 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 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 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 effect Figure 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