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Name: Alice
Status: student
Grade: 9-12
Country: Canada
Date: Winter 2012-2013


Question:
If air pressure increases with temperature, how come the poles are regions of high pressure? Should they not have low pressure?


Replies:
The idea that air pressure increases with increasing temperature is for a sealed container, not the open air. In the outside, pressure decreases with heating because the air expands and has less density.

Hope this helps. Bob Avakian Oklahoma State University Institute of Technology


You are probably invoking the ideal gas law: PV = nRT. In this case the pressure is proportional to the temperature. But that conclusion assumes the quantity of gas, n, and the volume, V, are constant. But the atmosphere is not a closed system!! So the ideal gas law is not immediately applicable. In addition, the atmosphere is not at ?rest?. There are winds and various wind currents that require a more detailed analysis.

Vince Calder


Alice,

For a constant volume of air, air pressure does increase with increased temperature.

However, as air temperature increases, it causes the air to expand, thereby increasing the volume, and perhaps also increasing the pressure if the air is prevented from expanding fully (by the weight of air above it, for instance).

So, one can not automatically say that air pressure increases with temperature.

There are a number of factors that determine both the temperature and pressure of an air mass, including the amount of energy that enters it (from solar radiation or from radiation from the ground or clouds), the reflectance of the surface of the Earth (which is greatest when there is snow on the ground and about 20% reflectance during the day from healthy vegetation), its location on the Earth, weather patterns and how they take the air over warmer or cooler surfaces of the Earth, etc.

Low pressure areas do form over the poles and create storms, although high pressure may tend to be more common in the polar areas.

David R. Cook Meteorologist Atmospheric and Climate Research Program Environmental Science Division Argonne National Laboratory


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