In
meteorology, an
air mass is a large volume of
air that have characteristics of
temperature and
water vapor content. Air masses cover many hundreds or thousands of square miles, and slowly change in accordance with the surface below them.
Air masses are classified according to their approximate environmental origin. An air mass is classified as Arctic, Polar, Tropical, or Equatorial. It is also classified as either maritime or continental. Maritime air is a moist air mass, whereas continental air is relatively dry.
Air masses are noted on some weather charts using a particular system of notation. However, air mass terminology is somewhat subjective, that is, it is not defined by any definite, universally-accepted quantitative parameters. It is used primarily for general descriptive purposes in meteorological discussions.
Air masses of oceanic origin are denoted with a lower-case "m" ("maritime"), while air masses of continental origin are denoted with a lower-case "c" ("continental"). Air masses are also denoted as either Arctic (upper-case "A", or "AA" for Antarctic air masses), polar (upper-case "P"), tropical (upper-case "T"), or equatorial (upper-case "E"). These two sets of attributes are used in combinations depending on the air mass being described. For instance, an air mass originating over the desert southwest of the United States in summer may be designated "cT". An air mass originating over northern Siberia in winter may be indicated as "cA".
