Air Mass 01
Air Mass 01 : General. (Meteor) A large (500 to 5000 mile diameter) definable, more or less uniform region of air bounded by fronts at which the properties (temperature, velocity, etc. change rapidly. Note: Air masses are classified according to their source region and the surface over which they have developed (symbol c for continental and m for maritime). Common types in the northern hemisphere are: Arctic (A) , a cold mass during all seasons; Polar Continental (cP), a cold mass occurring primarily during the winter; Polar Maritime (mP), a cold mass occurring during all seasons; Tropical Continental (cT), a warm mass prominent during the summer; Eguatorial (E), a warm mass occur-ring in all seasons; Monsoon (M), a dry mass in winter and wet mass in summer. The source region symbols are affixed with letters K and W to indicate whether the mass is colder or warmer than the surface over which it is moving. Horizontal convergence at low levels, associated with lifting, produces vertical instability of the upper air, and horizontal divergence, associated with sinking, produces vertical stability (designated u and s, respectively, on maps). Thus, for example, mPKu indicates a maritime, polar, cold, vertically unstable air mass
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