Air Mass: Meaning and Characteristics

Earth atmosphere is an envelope of mixture of gases, known as air. There are different gases such as nitrogen, oxygen, carbon dioxide, argon, etc. However, the properties of air are not uniform across the globe, but rather different in different region. In polar region, air is cold, in tropical region, air is warm. Such property defines the term air mass.

What is Air Mass?

In a technical language, an air mass is a huge volume of air, which temperature and humidity are uniformly same. Surprisingly, the are it covers, are very extensive. It covers, hundreds or sometimes, even thousands of square kilometers. Based on source of origin and its geographic presence, it classified as polar, arctic, maritime, etc.

Definitions

According to A.N. Strahler and A.H. Strahler:

"a body of air in which the upward gradients of temperature and moisture are fairly uniform over a large area is known as an air mass.”

According to -G. Trewartha:

“air mass is a three dimensional body of air having distinctive physical properties from the surrounding and relatively homogenous in terms of specific humidity, lapse rate and density.”

Nature of Air Mass

Nature of air mass largely defines the properties of air mass and it depends on the:

• Source of origin,

• Duration of air mass stability, and

• Natural changes or modification with time and space

Origin of Air Mass

An air mass does not origin in a day time or week time, but rather takes months and it originates over extensive areas of earth. However, some of the ideal conditions of its origination are:

• It requires an extensive area (it could be either land or water), which weather system need to be fairly uniform and calm.

• The temperature and humidity must be uniform.

• Air present in the region, must remain in contact with the region for long time.

• There should not by any external disturbance like divergent winds.

Because of presence of all these conditions, the air present in the region gradually acquires the property of the region, especially, the temperature and humidity, which gives the result of air mass.

Source Regions of Air Masses

A source region of air mass defines the geographic region over which the respective air mass developed. It is usually a vast area of land or water (ocean surface) over which the temperature and humidity are uniformly distributed. It is important to note that air must be uniform on a large scale over the source area so that there would have sufficient opportunities to form air mass. Such an ideal condition helps the entire air of the region to acquire the properties of given region, especially the homogenous properties of temperature and humidity.

The major source regions for air mass development are:

• Arctic and Antarctic Source Regions: It is the region around the north pole and south pole respectively. It has uniform property of extremely cold conditions. Likewise, very cold air masses originate in these regions.

• Continental Polar Source Region: Specifically, in the norther hemisphere, there is extensive land area and because of having fairly cold weather for longer period of time, offers a good opportunity for the formation of cold air mass. This is the region, where temperate cyclone develops.

• Maritime Polar Source Region: The maritime polar sources are found over the vast areas of the oceans. Specifically, the northern part of the Atlantic Ocean and the eastern part of the Pacific Ocean provide suitable conditions for air mass formation.

• Continental Tropical Source Region: The larger land area of tropical region is ideal source region for tropical air mass. These source regions specially develop in Asia and North Africa.

• Maritime Tropical Source Region: These source regions are largely found over the water surface of the tropical region. In summer as well as in winter, it provides suitable opportunities for the development of air mass source regions.

• Maritime Equatorial Source Region: Equatorial region has fairly uniform weather condition throughout the year. Secondly, this is the region where the north and the south winds converge and give rise to maritime equatorial sources region.

Characteristics of Air Mass

Following are the major characteristics of Air Mass:

• The air mass acquires its properties (especially temperature and humidity) from its source region; for example, in the polar regions, air masses are freezing cold; in the temperate region, it is cold; in the tropic region, it is warm to hot, etc.

• To develop an air mass, there must be a very large area, which has relatively uniform temperature and humidity.

• The temperature and humidity of air mass are fairly homogenous that maintains throughout its life span.

• The entire air mass move in unity and while moving from one region to another region, it maintains its homogenous characteristics and hence remains different from the surrounding air.

Conclusion

Air mass is one of the most significant and essential functions of the troposphere (i.e. lower atmosphere) of the earth. It maintains and regulates the weather system of respective geographic regions. Importantly, the characteristics of the air mass depends on its source region where it develops.

Frequently Asked Questions

What are the major factors that determine the characteristics of an air mass?

The major factors that determine the characteristics of an air mass are origin source. If the source region is cold, then the air mass will be cold and if the source region is warm, then the air mass will be warm and likewise.

Can the characteristics of an air mass change especially when it moves from origin source to other region?

Definitely, the characteristics of an air mass change, when it moves from one region to another. The reasons are its interactions with underlying surface, mixing with other air, which property is different, etc.