The dry area on the lee side of a mountain that forms as air descends and warms by compression is called a rain shadow.

Here's a breakdown:

* Lee side: The side of a mountain that faces away from the wind.

* Descending air: As moist air rises up the windward side of a mountain, it cools and condenses, leading to precipitation. This now drier air then descends on the lee side.

* Compression: As the air descends, it is compressed by the increasing air pressure at lower altitudes. This compression causes the air to warm.

* Dry conditions: The warming air has a reduced capacity to hold moisture, leading to dry conditions on the lee side.

This phenomenon creates a distinct difference in precipitation patterns, with the windward side of the mountain often experiencing significantly more rain or snow than the leeward side.