T/G Layout 1

Now that we understand the overall circulation patterns of the atmosphere, we can

re t u rn to the energy balance issue; the transport of heat from the equator to the poles.

The southernmost cells of the general circulation (Hadley and Ferrel) are fairly efficient in

t r a n s f e rring heat directly from the tropical regions. In the mid-latitudes, the general circ u-

lation and the Coriolis effect combine to produce conditions less favorable to energ y

t r a n s f e r. The mid-latitude, westerly winds are opposed by easterly winds produced by

polar air sliding southward (figure 10). Due to diff e rences in density, the two air masses

do not readily mix and the transfer of warm air poleward is re t a rded. How then is heat

t r a n s p o rted poleward across the mid-latitudes to re s t o re balance to the system?

The mechanism which transports energy poleward in the mid-latitudes is the cyclonic dis-

turbance. On satellite images, the distinct comma cloudp a t t e rn associated with these

s t o rms indicates the energy transfer. The process by which the transfer of warm air pole-

w a rd occurs is summarized in qualitative terms in figure 11 (page 23). The process begins

with the transport of warm air to the mid-latitudes. As noted above, this air mass does

not readily mix with denser polar air. Over time, the west winds in the mid-latitudes con-

tinue to absorb heat transported nort h w a rd and a strong latitudinal t e m p e r a t u re gra-

dient develops with increasingly warm air bordering on cold polar air. As the gradient

becomes pro g ressively stro n g e r, a small disturbance, which is often associated with the

movement of smaller scale waves and the stru c t u re of the jet stream, begins to amplify.

Over time, a large wave develops which sweeps warm air poleward and finally heat is

exchanged. The latitudinal temperature gradient decreases and stable conditions re t u rn.

Earth’s weather patterns are a result of the unequal heating of the Earth’s surface. The trop-
ical latitudes receive more energy from the Sun than the higher latitudes.

Averaged over Earth, incoming radiation from the Sun approximately equals outgoing Eart h
radiation. However, this energy balance is not maintained in all latitudes—the tropics experi-
ence a net gain, the polar regions a net loss.

The Eart h - a t m o s p h e re system attempts to
re s t o re balance to the system by transport-
ing excess energy from the equatorial
regions to the poles.

D i ff e rences in pre s s u re within the atmos-
p h e re cause air to move—wind to blow.

General atmospheric circulation re p re s e n t s
average air flow around the world. Actual
winds at any location may vary consider-
ably from this average.

Wind direction is given as the dire c t i o n
f rom which the wind is blowing, i.e., a
n o rth wind blows from north to south.

f i g u re 10.

Coriolis Effect & General Circulation

horse

latitudes

horse

latitudes

doldrums

high pressure

high pressure

low pressure

60 o

30

o

0

o

60 o

30 o

northe ast trades

prevailing westerlies