Structure of the Earth’s Atmosphere

* Chemical Composition* Vertical Layers* Coriolis Force* Hadley Cells

Current Composition

Atmospheric Composition today

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.

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

MesosphereMass 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

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.

Hadley Cells

Hadley, Ferrel, Polar Cells

Earth’s atmosphere divides into 3 cells. Coriolis deflection 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

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 Coriolis force 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

Coriolis Effect 6 min YouTube (start 1min in for merry-go-

round demo)