- For airmass in astronomy, see airmass.
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.
Movement and fronts
Air mass terms refer to the fact that air masses acquire characteristics from a given region which they may occupy for any significant length of time. For example, Polar air masses form during the northern winter as intense nighttime radiation and loss of daylight chills the air to great depths, and maritime air masses generally form over oceans and seas where widespread evaporation occurs. When air masses move into regions with different environmental conditions, they are modified. Even without movement, air masses can vary gradually over distance, with one type gradually becoming another. The boundary between two air masses can also be comparatively sharp. Where it is, the boundary is termed a "front". Fronts are often characterized by inclement weather, and are usually associated with areas of low atmospheric pressure termed frontal systems.
See also
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