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 AtmosphereThe 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 coldd. 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

From Cunningham & Cunningham, 2004, Fig. 9.2

Reflected = 25 + 5 = 30

Absorbed = 25 + 45 = 70