Polar Air Pressure
Date: Spring 2012
Why does air pressure tend to be higher over the poles and lower over the equator? Is this due to Earth's spinning faster at the equator?
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Note where the direction of the wind circulation is up and down (not horizontal).
Wherever the wind comes down is a high pressure area
Wherever the wind goes up is a low pressure area.
Just like air pressure on an object, like a birthday cake, goes up when you blow on it to blow out the candles.
Note in the picture that over the poles, on a word-wide scale, the wind is descending and thus the air pressure at the poles is higher.
However, local variations occur all of the time and there are times when this is not so.
It has more to do with temperature. The equator is heated by the sun more than the poles, so the heated air rises, leaving lower pressure at the surface. At the poles, the dense cold air flows out toward the equator under its own weight, just as honey poured into water will flow outward, lifting the water it displaces.
Richard E. Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
Earth's general atmospheric circulations (called Hadley cells)
cause air to rise in the northern mid-latitudes and move northward.
The air, now cooled in the upper atmosphere, then sinks downward in
the Arctic or Antarctic. The descending air results in a high
pressure system; there is more mass of air in a column of air above
the surface since you are constantly piling air on top of the column
of air, and generally easterly winds. The high pressure system is
often cut off from the atmospheric systems to the south and thus
becomes almost self-sustaining.
At the equator the air is always rising because of intense heating by
the Sun. Rising air results in less air in the column of air above
the surface and thus low pressure.
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: June 2012