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Atmospheric Circulation


The global energy balance and atmospheric motion mainly
determine the circulation of the earth's atmosphere. There
is a hierarchy of motion in atmospheric circulation. Each
control can be broken down into smaller controlling
factors. The global energy balance is an equal balance of
short-wave radiation coming into the atmosphere and
long-wave radiation going out of the atmosphere. This is
called thermal equilibrium. The earth is at thermal
equilibrium; however, there can have a surplus or deficit
of energy in parts of the heat budget. If you have a net
radiation surplus warm air will rise, and a net radiation
deficit will make the air cool an fall. Air gets heated at
the equator because of the inter tropical convergence zone
and rises to the poles. There the air is cooled and it
floats back down to the equator where the process is
repeated. Another major contributing factor to the
circulation of the air is due to the subtropical highs.
These highs like the ITCZ migrate during the different
The idealized belt model is a great representation of the
general circulation of the atmosphere. The equatorial belt
of variable winds and calms ranges from 5 degrees north to
5 degrees south. This wind belt is characterized by weak
winds and low pressure from the inter tropical convergence
zone. As you go further north or south you encounter the
Hadley Cells. Hadley cell circulation is caused by the
movement of high pressure from the latitudes at 5 to 30
degrees north and 5 to 30 degrees south to low pressure
areas around the equator.
The movement of air from high pressure to low pressure
causes convergence. This convergence generates the
production of wind. The winds that are produced from this
are the trade winds. The winds blow from a northwest
direction in the northern hemisphere, and in the southern
hemisphere the winds blow from a southeast direction. The
trade winds are the largest wind belt. The westerlies, they
lie between 35 and 60 degrees north and south latitude. The
wind blows from the west , thus their name. The westerlies
are in the Ferrell cell. Cold air from the polar regions
falls down and then is heated up and pushed upward with the
westerlies. >From 65 to 90 degrees north and south lie the
polar easterlies. It exists because of the pressure
gradient that is created by the temperatures. The winds are
also deflected by the coralias effect. This deflection air
is to the right in the northern hemisphere, and to the left
in the southern hemisphere. The reason that this happens is
because of the rotation of the earth on its axis.
Two moving patterns of the general circulation of the
atmosphere are the cyclones and anticyclones. Cyclones are
low pressure systems characterized by converging and rising
air. On the other hand anticyclones are characterized by
high pressure because they have diverging air that is
descending. There are also land and sea breezes which are
produced by daily differences in cooling and heating of the
land and water. Sea breezes bring cooler air in the day,
while land breezes push cooler air over the water at
There also exists radiation surpluses and deficits through
out the earth. There is a constant surplus between the
latitudes of 15 degrees north and 15 degrees south. In the
latitudes between 15 and 38 degrees north and south there
is a net radiation surplus that varies annually. There is a
net radiation deficit annually in the latitudes from 38 to
90 degrees north and south. These surpluses and deficits
are due to the high sun angle in the low latitudes, as well
as the increased length of daytime.
Finally the seasons of the earth are determined by the tilt
of the earth on its axis. The earth is on a tilt of 23.5
degrees. When it revolves around the sun the earth is
exposed to the sun at different degrees at different months
of the year. Because of this phenomenon we get seasons on
the earth. The earth and all of its circulation patterns,
energy balances, and motions of the atmosphere are all very
complex; however, it can be easily understood by my
wonderful summary.


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