Basic Properties of the Atmosphere

Composition of the Atmosphere Nitrogen (78.08% ~ 78%) Oxygen (20.95% ~ 21%) Argon 0.93% (9300 parts per million) Carbon Dioxide 0.035% (350 ppm) Neon 18 ppm Helium 5.2 ppm Methane 1.4 ppm Ozone 0.07 ppm

Other Components of the Atmosphere Water Droplets Ice Crystals Sulfuric Acid Aerosols Volcanic Ash Windblown Dust Sea Salt Human Pollutants

Structure of the Atmosphere The atmosphere is thicker at the equator, thinner at the poles 4 Levels Defined by Temperature a. Troposphere (cools farther from surface) Where Weather (moisture) Happens b. Stratosphere Ozone Layer (O3), blocks ultraviolet radiation c. Mesosphere- gets way cold d. Thermosphere- hot due to large amount of solar radiation, but you freeze b/c low # of molecules! Includes the Ionosphere (Northern Lights)

Troposphere (0 – 15km) Temperature of 20C at surface to -60C at 15km Convection Currents: Heating rock and water at the Surface creates warm air at surface, Warm air rises, but air expands as it rises and cools as it expands, then it sinks again Two opposing action = constant turnover, keeps our atmosphere mixed.

Stratosphere Altitude 15-50 km Temperature increases with altitude -60 C at base to 0 C at top Reason: absorption of solar (ultraviolet) energy to make ozone at upper levels (ozone layer) Ozone (O3) is effective at absorbing solar ultraviolet radiation

Mesosphere 50 – 80 km altitude Temperature decreases with altitude 0 C at base, -95 C at top Top is coldest region of atmosphere

Thermosphere 80 km and above Temperature increases with altitude as atoms accelerated by solar radiation -95 C at 80km to +100 C at 120 km Cannot feel the heat. Traces of atmosphere to 1000 km Formerly called Ionosphere

Why is the Mesosphere so Cold? Stratosphere warmed because of ozone layer Thermosphere warmed by atoms being accelerated by sunlight Mesosphere is sandwiched between two warmer layers, nothing warms it up.

Composition and Altitude Up to about 80 km, atmospheric composition is uniform (troposphere, stratosphere, mesosphere) Above 80 km light atoms like hydrogen and helium rise above the other heavier molecules of nitrogen and oxygen..

What happens above 120 km Below 80 km, an atom accelerated by solar radiation will very soon hit another atom Energy gets evenly distributed in the atmosphere Above 80 km atoms rarely hit other atoms Light atoms get accelerated and have more movement and fly higher, but few atoms escape entirely

Atmospheric Layers

Energy Balance Reflected = 25 + 5 = 30 Absorbed = 25 + 45 = 70 From Cunningham & Cunningham, 2004, Fig. 9.2