An air mass usually forms in an area of

When a large body of air remains over an area for several days or weeks, the body of air may change its thermal and moisture properties according to the land or water under it. The air exchanges heat with the land or water, either warming or cooling, until its temperature closely matches that of the surface below it. The body of air also gains or loses moisture depending on the temperature and moisture content of the surface. A body of air that resembles the characteristics of the surface under it is called an air mass.. Does this help ?

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