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 seasons.
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 nighttime.
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
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.