Structure of the Earth’s Atmosphere

1. Structure of the Earth’s Atmosphere * Chemical Composition * Vertical Layers * Coriolis Force * Hadley Cells

2. Current Composition

3. Atmospheric Composition today

5. Troposphere • Surface layer - 30,000 ft • Heated from below • General T structure dec. w/height • Convection - weather, clouds form from rising air which cools by pressure drop, and clouds dissipate as air falls and heats.

6. Stratosphere • Heated by ozone absorbing UV light • UV breaks apart ozone into O2 + atomic oxygen - get energy release and heating. • higher altitudes efficiently absorbs UV at 200 and 350 nm. • lower altitudes less efficiently absorbs UV at 44 and 80 nm • Temperature inversion - no convection, no weather. • 7 – 30 miles

7. Mesosphere • Mass of atmosphere 0.1% • Density is too low for ozone chemistry to heat • get normal trend we saw in troposphere– lower T with inc. altitude. • 30-50 miles

8. Ionosphere (= Thermosphere) • Density so low Space Shuttle orbits here, with little drag • T can be very high; 4,000F. • But no significant heat because density low. • Heated by ionization by UV from the sun, and the solar wind.

9. Hadley Cells

10. Hadley, Ferrel, Polar Cells • Earth’s atmosphere divides into 3 cells. • Coriolisdeflection sets the major constraint on how many cells the atmosphere of a planet divides into. • stronger for more rapid rotation. • size of the planet and speed of rotation • which determines number of cells

11. Hadley Cell • Solar heating at equator is strongest - causing rising convective air which is pushed north and south at the tropopause • At ~30deg latitude deflected enough by Coriolisforce to be moving almost due east. • Meets air moving down from the north (Ferrel Cell air) and both descend, warming and drying • Trade Winds - return of surface wind to equator

12. Coriolis Effect • 6 min YouTube (start 1min in for merry-go-round demo)