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Name: Dale
Status: educator
Grade: 9-12
Location: NC
Country: USA
Date: N/A 


Question:
What happens to the heat energy release to surrounding air when air cools by rising?


Replies:
Dale,

As an air parcel rises, it cools, assuming that it's rising through air that is cooler (and/or has lower atmospheric pressure) above it. The air parcel will also expand as it rises, in the decreasing pressure with height. The energy released from cooling of the parcel is radiated to the air surrounding the parcel, thereby warming that air. This tends to cause the parcel and the air surrounding it to approach a temperature equilibrium. However, since the parcel has momentum in rising, that equilibrium is not reached and the parcel continues to rise, unless the decrease in temperature of the surrounding air with height is so small as to allow sufficient time for the equilibrium to occur or the decrease in temperature with height of the surrounding air ends.

David R. Cook


There actually is not very much heat transfer between a rising air parcel and the air surrounding it. Air parcels are so large and the rate of heat transfer so slow that the processes are very close to adiabatic.

When air cools by rising, it does not do so by heat transfer. The rising air does work by expanding, and in so doing it lowers its own internal energy. Basically, since the rising and expanding air parcel moves the surrounding air outward, the air molecules in that parcel don't rebound as fast when they collide with a retreating target.

Now, the descending air that replaces the rising parcel has exactly the opposite process occurring--it is compressed by the surrounding air, which makes its molecules move faster. So the rising becomes cooler and the sinking air becomes warmer, but that is not due to heat transfer between them.

Richard E. Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming



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