(physics, meteorology) a widespread body of air, the properties of which can be identified as: (a) having been established while that air was situated over a particular region of the Earth's surface (airmass source region) and (b) undergoing specific modifications while in transit away from the source region. An air mass is often defined as a widespread body of air that is approximately homogeneous in its horizontal extent, particularly with reference to temperature and moisture distribution; in addition, the vertical temperature and moisture variations are approximately the same over its horizontal extent.

plural of airmass

(physics, meteorology) An extensive area of the Earth's surface over which bodies of air frequently remain for a sufficient time to acquire characteristic temperature and moisture properties imparted by that surface. Air so modified becomes identifiable as a distinct air mass. See airmass.

plural of airmass source region