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SECTION 6. AIR MASSES

1. General

a. The various air masses take on the temperature and moisture characteristics of the
areas in which they are formed--the coldness of the polar regions, the heat of the tropics, the
moisture of the oceans, and the dryness of continents.

b. As they move away from their source regions and pass over land and sea, air
masses are constantly being modlfied through heating or cooling from below, rising or
descending or gaining or losing moisture. In general, however, they keep their orlginal
characteristics and can be recognized and identified as they move over the surface of the
earth.

2. Movement of Air Masses

Since the general movement of the atmosphere in the United States is toward the east, the
polar and arctic air masses generally move toward the south- east, and the tropical and
equatorial air masses move toward the northeast. The speed varies according to the season
and the type of the air mass, but Cold air masses move it generally averages from 500 to 700
miles a day. a little more rapidly than warm air masses