The Airmass Concept

An airmass is defined as a large body of air whose physical properties (temperature, moisture content and lapse rate) are more or less uniform horizontally for hundreds of kilometres. The theoretical ideal is a barotropic atmosphere where surfaces of constant pressure are not intersected by isosteric (constant-density) surfaces, so that in any vertical cross-section, as shown in Figure 9.1, isobars and isotherms are parallel.

Three factors determine the nature and degree of uniformity of airmass characteristics: (1) the nature of the source area where the airmass obtains its original qualities; (2) the direction of movement and changes that occur as an airmass moves over long distances; and (3) the age of the airmass. Airmasses are classified on the basis of two primary factors. The first is temperature, giving arctic, polar and tropical air, and the second is the surface type in their region of origin, giving maritime and continental categories.

Continue reading here: Nature Of The Source Area

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