In Meteorology, the air mass is the large body of air having nearly uniform characteristics of temperature and humidity at any given level of altitude. Such a mass has a distinct borderline and may outstretch hundreds or thousands of kilometers horizontally and sometimes as high as the troposphere ( about 10-18 km [ 6 -11] miles above the Earth’s surface. An air mass is formed whenever an atmosphere gets in touch with a large, relatively stable land or sea surface for long enough periods to receive the temperature and moisture of that surface.
Air masses are commonly classified concerning the latitudes, and their continent or maritime source regions. Colder or freezing air masses are termed polar or arctic, whereas warmer air masses are deemed tropical. Maritime and monsoon air masses are moist whereas continental and superior air masses are dry.
Air Mass Definition
“An air mass is defined as the large mass of air whose physical features such as moisture, temperature, lapse rate, and content are approximately uniform horizontally for hundreds of kilometers”.
According to A.N, Straheler, and A.H. Straheler (1978), a large body of air in which an upward rise of temperature and moisture are fairly uniform over a large area is known as an air mass.
Types of Air Masses
The most common types of air masses are maritime polar(mP), maritime tropical (mT), continental tropical (cT), continental polar (cP), and continental arctic (cA).
Maritime Polar (mP) Air Mass- The maritime polar air mass is cold and humid originating from the oceans in the polar latitudes.
Maritime Tropical (mT) - The maritime tropical air mass is warm and humid originating from the oceans in the tropics.
Continental Polar (cP) - The continental polar air mass is cold and dry originating from land regions in the polar latitudes.
Continental Tropical (cT) - The continental tropical air mass is hot and dry originating from land in the tropics.
Continental Arctic (cA) - The continental arctic air mass is dry originating from the North pole.
Continental Antarctica (cAA) - The continental antarctic air mass is extremely cold and dry originating from land at the south pole.
Look at the image given below to observe from where these different types of air masses typically originate.
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Air Mass Creation
Air masses are developed when air is present to the surface over an extended period. This generally occurs at high temperatures with light winds. The area where air masses develop is known as the source area. Air masses over the warmer surface develop much faster than the colder surface because there is a weaker disturbance in the stable air over the cold surface. When the air masses get shifted from their source region, they change over time due to the surface and the area over which the air masses flow.
Air Masses Movement
Air masses do not stay over their source location for a long period. As the weather pattern changes slightly, air mass gets shifted to a new location. Two things occur as the air mass moves towards a new location. First, as the air mass shifts over different surface characteristics, it begins changing. This process is known as air modification. For example, a maritime polar air mass that moves from the Pacific oceans over the mountains in the western continental US will sometimes dry as it crosses over the mountains, wash away its moisture, and warm over the land surface until it becomes the continental tropical air mass. The second thing that occurs when air mass moves is that they can hit the other air masses. When two air masses hit, a boundary known as the front is developed.
Did You Know?
Maritime tropical air masses are often referred to as the trade air mass.
Continental Polar masses are dry and cold because of their continental source regions.
The continental polar mass that affects North America develops over interior Canada.
Colder air masses are known as polar or arctic whereas warmer air masses are known as tropical.
Five air masses that affect the United States around the time of a typical year are maritime polar, maritime tropical, continental polar, continental tropical, and continental arctic.
The stability of air mass can be represented using the third letter either ‘k’ ( air mass colder than the surface below it ) or ‘w’ ( air mass warmer than the surface below it). An example of this can be a polar air mass blowing over the Gulf airstream, represented as cPk.