What is an air mass?

An air mass is a large volume of air in the atmosphere that is mostly uniform in temperature and moisture. Air masses can extend thousands of kilometers in any direction, and can reach from ground level to the stratosphere – 16 kilometers into the atmosphere.

What is a source region?

The region where an air mass acquires its characteristic properties of temperature and moisture is called its source region. Ocean areas, snow- or ice-covered land areas, and wide desert areas are common source regions.

Air masses form over large surfaces with uniform temperatures and humidity, called source regions. Low wind speeds let air remain stationary long enough to take on the features of the source region, such as heat or cold. When winds move air masses, they carry their weather conditions (heat or cold, dry or moist) from the source region to a new region. When the air mass reaches a new region, it might clash with another air mass that has a different temperature and humidity. This can create a severe storm.

What are the major types of air masses as per the source region?

As per the source region, the following are the major types of air masses on the earth:

1 . Maritime Tropical (mT) air mass ( Source region: Warm Tropical and subtropical ocean;)

2 . Continental Tropical (cT) air mass ( Source region: Subtropical Hot desert)

3 . Maritime Polar (mP) air mass ( Source region: Relative cold high latitude ocean;)

4 . Continental Polar (cP) air mass ( Source region: Cold snow-covered Continents in high latitudes)

5 . Continental arctic (cA) air mass ( Source region: Permanent ice cover continents in the arctic and antarctic)

6 . Maritime arctic (mA) air masses (Source region: arctic ; moist and cold)

What are the major types of air masses on the basis of moisture content?

Based on the moisture, there are two types of air masses:

1 . Dry Air mass : Dry air masses usually originate on continents. The “continental tropical (cT)” air mass is an example of a dry air mass.

2 . Moist Air mass : Moist air masses are generated over the oceans. The “maritime tropical(mT)” air mass is an example of a moist air mass .

How air masses are formed?

When air stays longer over a homogeneous region such as a plain or large ocean (preferably an equal insolation region), they acquire the prevailing surface temperature (cold/warm) and humidity properties.

The low wind speed helps the large area of air to remain stable for a longer period of time and helps to obtain the characteristics of the source area such as temperature, and humidity.

The formation of air masses requires homogeneous surfaces (eg oceans, large plains, deserts) and homogeneous insolation.

What is the time required for the formation of air masses?

The time required for a body of air to come to approximate equilibrium with the surface over which it is resting may vary from a few days to 10 days or 2 weeks, depending largely on whether the body of air is initially colder or warmer than the temperature of its source region.

If the air is colder, it is heated from below. Convective currents are produced, which carry the heat and moisture aloft and rapidly modify the air to a considerable height.

On the other hand, if the air is initially warmer than the surface, it is cooled from below. This cooling stabilizes the air and cuts off convection. Cooling of the air above the surface must take place by conduction and radiation, and these are slow processes. Thus, a longer time—up to 2 weeks—is required for the development of cold air masses, and even then these air masses are only a few thousand feet thick.

What are the major functions (impact) of Air masses?

1 . Air masses move from one region to another, with the movement they also transfer heat, cold, and moisture from the source region to the destination region.

2 . According to the monsoon wind theory, the arrival of the monsoon is due to the transfer of oceanic tropical (mT) air masses to the Indian continents.

3 . Temperate cyclones and fronts are formed as a result of the interaction of two different air masses.

What is air mass modification?

Modification or transformation of air mass occurs when air masses move from their source region to another region. Where the air mass moves, there is an exchange of heat, cold, and moisture with the underlying surface.