1. Atmospheric Circulation

Thermosphere

MesosphereStratosphereTroposphere

300 km

50 km

40 km10 km

400 km altitude

Exosphere

is the Earth’s 110 km thick gaseous envelope, andevolved in three stages:

4-4.5 Ga agodominantly H, He (much like Jupiter, Saturn and Sun)

3.5 Ga ago changed to mostly C, N and O when the first oceans appeared

1.25 Ga agobecame mostly N and O, as at the present time, because of loss of C. Where did this atmospheric

CO2 go? It ended up in the oceans. How? Because of

photosynthesis.

Troposphere

extends to 16-18 km above the tropics but <10 km above the poles;

contains ~80% of atmosphere’s mass; and

runs the hydrological cycle because tropo-spheric temperatures decrease with height.

Stra

tosp

he

reS

trato

sph

ere

StratopauseStratopause

Me

so

sph

ere

Me

so

sph

ere

MesopauseMesopause

Th

ermo

-T

herm

o-

sp

he

res

ph

ere

TropopauseTropopause

TroposphereTroposphere

Average temperature, °C

Hei

gh

t, a

bo

ve m

ean

sea

lev

el (

km)

Average atmospheric temperature

What if the tropo-spheric temperature

gradient changes?

Why is ozone good overAntarctica but bad over Southern California?

There is a hole in the Ozone layer right above Antarctica

Sun is so far that we can assume Sun’s rays striking the Earth’s surface to be parallel. Because of the curvature of

Earth’s surface, then, solar heat input varies with latitude.

Sam

e in

pu

t

Tropics thus receive most solar heat per unit area

and the polar region the least.

Why seasons?

Earth's spin axis tilts 23.5° from the vertical. Thus, as Earth completes is orbit, North pole tilts towards the Sun one-half the time, with peak at the Summer Solstice, whereas South pole tilts towards the Sun during the other half, with peak at Winter Solstice. Tropics, bounded by Tropic of Cancer (23.5°N) and Tropic of Capricorn (23.5°S), receive Sun all year round and therefore have no seasons, whereas temperate latitudes have seasons. Also, the northern temperate region (23.5°N to 66.5°N or the Arctic Circle) has summer when the southern temperate region (23.5°S to 66.5°S or the Antarctic Circle) has winter, and vice versa. What if Earth's spin axis became nearly vertical, as is the case with Venus? Will we still have the seasons?

What if Earth's spin axis became vertical, much like what exists on Venus? Will we still have the seasons?

Differential heating:Tropics receive most solar heat.Differential gravity:Gravitational acceleration is most at the poles, least at the equator. Differential rotation:Equatorial surface wind blows to the west, against the direction of Earth’s spin.

A general model of tropospheric circulation3 forces govern this circulation:

The Patterns in Global Air Circulation

30° N

60° N

30° S

60° N

0°

Rotation has consequences for Weather

Because of rotation, surface air blows increasingly to the west the closer we approach the equator.

This is Coriolis effect and is demonstrated in the followinganimation.

Majo

r surface w

ind

pattern

s

http://web1.umkc.edu/sites/env-sci/module4/weblab4.htm

Satellite images of particles (aerosols) in the atmosphere are one way to illustrate the path of global atmospheric circulation. The animation below shows daily global images of the Total Ozone Mapping Spectrometer (TOMS) aerosol index indicating the location of UV-absorbing tropospheric aerosols from July through September, 1988. Here, light brown indicates the smallest amount of dust/smoke in the atmosphere, with dark brown indicating the largest amount.

N

S

EW

http://ingrid.ldgo.columbia.edu/maproom/.Global/.Climatologies/Precip_Loop.html

Seasonal temperature variations can be explained in terms of the latitudinal and seasonal variations in the surface energy balance. The pattern of temperatures are a function of net short-wave radiation, net long-wave radiation, sensible heat flux, latent heat flux and change in heat storage.

http://geography.uoregon.edu/envchange/clim_animations/

Precipitation-Evaporation (P-E) represents the difference between precipitation and evaporation

http://geography.uoregon.edu/envchange/clim_animations/

Some implicationsAt 30°N/S latitudes, sea surface salinity tends to be high and deserts tend to cluster on land.When equatorial surface wind blows to the west, it also stacks the warm surface waters to the west, so producing the E—W temperature differential that produces the hurricanes and cyclones that strike eastern margins of tropical/semitropical land.

http://www.scivis.nps.navy.mil/~braccio/images/S_big.gif

Sea Surface Salinity

http://pubs.usgs.gov/gip/deserts/what/world.html

Deserts tend to cluster about 30º North and South latitudes, towards the western margins of land.

Tropical cyclones develop in the hot, humid air over a sea surface exceeding 26°C in temperature.

Hurricanes typically occur on our Atlantic coast and originate

farther to the east, as can be seen in this animation of

Hurricane Katrina.