Temperature and humidity may change a bit horizontally across the air mass, but not too
much. An air mass may have more changes with altitude.
Meteorologists use symbols to describe the characteristics of an air mass. The first symbol
tells whether the air mass had its origin over a continent (c) or over an ocean (m, for
maritime). As you might expect, air masses that form over oceans contain more water vapor
than those that form over land. The second symbol tells the general latitude where the
air mass gained its temperature and humidity traits. The categories are arctic (A), polar
(P,)tropical (T), and equatorial (E). Of course, air masses that form over polar areas are
colder than those that form over tropical regions.
Globally, the major air masses are continental arctic or continental antarctic(cA or cAA);
continental polar (cP); maritime polar (mP); continental tropical (cT); maritime tropical
(mT); and maritime equatorial (mE). Maritime arctic and continental equatorial air masses
rarely form.
Figure 16.14: The source regions of air masses found around the world. ( 11 )A third symbol takes into account the properties of an air mass relative to the ground it
moves over. If the air mass is colder than the ground, it is given the designation k, for cold.
If it is warmer than the ground, it is given the designation w. For example, a cPk is an air
mass with a continental polar source region that is colder than the region it is now moving
over.
Air Mass Movement
Air masses are pushed along by high-level winds, although they move slower than the winds.
An air mass gets its characteristics from the ground or water it is above, and it also shares
those characteristics with the regions that it travels over. Therefore, the temperature and
humidity of a particular location depends partly on the characteristics of the air mass that
sits over it.