The American Meteorological Society defines an air mass as

A widespread body of air, the properties of which can be identified as 1) having been established while that air was situated over a particular region of the earth’s surface (airmass source region), and 2) 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. The stagnation or long-continued motion of air over a source region permits the vertical temperature and moisture distribution of the air to reach relative equilibrium with the underlying surface.

Air masses are typically classified by their temperature and moisture content. They can either be hot or cold; wet or dry. Hot air masses originate over the tropics and are called tropical (T) and cold air masses originate over the poles (P). Air masses that form over the ocean are called maritime (m), while those forming over land are called continental (c). When combined, we have four different types of air masses: continental tropical (cT), maritime tropical (mT), continental polar (cP), and maritime polar (mP). There is a fifth type of air mass called arctic (A) that is just a very cold continental polar air mass. The figure below shows the air masses that affect the United States, and paths they could take.

When two different air masses converge, they produce a front. In future posts I’ll define the different kinds of fronts and what weather can be expected from them.

(No Ratings Yet)

 Loading ...

Related Posts:

Trackback URI |