Air Masses

Air masses are distinct from cloud forms. Hence, they are studied separately in meteorology. These masses cover thousands of miles horizontally across the Earth’s surface, and have typically the same temperature and moisture levels.

Having a solid grasp of this topic is essential to help individuals crack competitive exams. On that note, we have exclusively covered this topic for students preparing for UPSC and IAS exam.

Based on the UPSC Syllabus, the links given below answer various questions on air mass and its aspects. Aspirants can refer to the same for exam preparation:

What is air and its composition? What is an air mass and how does it form?
What are the characteristics of an air mass? What is an air mass?
What are the 5 types of air masses? What kind of air mass is found on seas and oceans?

Air Mass Definition

Air mass can be defined as a large air volume with uniform temperature and moisture. These masses can stretch thousands of miles horizontally over the Earth’s surface, and vertically from ground level to the stratosphere (10 miles) into the atmosphere.

How do Air Masses Form?

Air masses form over source regions that give them their uniform temperature and humidity. Moreover, low wind speeds prevent these large volumes from moving. So, while they stay stationary over a region, they acquire the conditions of that region, either temperature or humidity. Then as wind speeds increase, they move to other areas, still keeping their source region’s states.

They can also clash with different air masses in other regions and cause storms.

Categorisation of Air Masses

Meteorologists classify air masses based on where they are formed. Here is the classification.

Typically, there are 4 types of air masses:

  • Arctic: These air masses form in the Arctic region and are very cold.
  • Tropical: These air masses form in low lying latitudes and are warm up to a moderate level.
  • Polar: These air masses form in the high-latitude region and are cold.
  • Equatorial: They start forming over the Equator and are warm.

Besides this classification, there is another way to categorise air masses. Meteorologists classify them based on whether they form over water or land. These distinctions are:

  • Maritime: Maritime ones form over the water bodies and are filled with moisture.
  • Continental: Whereas, the Continental ones form over the land and are arid.

For instance, an air mass formed over interior Asia is a continental polar air mass that is cold and dry. However, one that is formed over the Indian Ocean is a tropical air mass that is humid and warm.

UPSC CSE aspirants can also refer to the following related links:

Factors Controlling Temperature Distribution Distribution of Temperature in the Earth’s Atmosphere
Temperature Inversion What conditions favour a temperature inversion?
Heat Index What is the difference between humidity and precipitation?

How to Read Air Masses on Weather Maps?

The notation that is used to classify an air mass consists of a lowercase letter followed by a capital letter, followed by another lowercase letter.

  • The first lowercase letter describes whether the air mass is dry or humid, continental or maritime.
Maritime or moist m
Continental or dry c
  • The second capital case letter describes the heat of this air mass.
Equatorial E
Polar P
Antarctic or Arctic A
Superior S
Tropical T
  • The third lowercase letter denotes the relationship between the ground and the air mass.
The air mass is colder than the ground below it k
The air mass is warmer than the ground below it w

Air Mass Categorisation of the USA

  • Continental Polar

This type of air mass forms over large land masses like Northern Canada. Mostly stable, these are free of condensation forms as they form over the land. When these air masses get heated or moistened from the ground, they are capable of producing snow or rain.

  • Maritime Polar

They form over large water bodies and pick up considerable moisture. They move towards the land in middle and high latitudes. They are responsible for producing heavy rain when forced up mountain slopes or can be caught up in cyclonic activity.

  • Continental Tropical

This type of air mass emerges in the lower latitudes over deserts or interiors of land masses. They usually develop in summer. It is subject to great heat, and due to the lack of moisture on the ground, they are typically arid.

  • Maritime Tropical

They form over the vast tropical oceans and contain much moisture. They are responsible for producing rain. In case it moves polewards, it is cooled by the ground surface and produces fog. Over the continental areas, they are strongly heated and responsible for convectional rain or thunderstorms.

To sum up, air mass is an essential topic for UPSC as it delves into details of the weather conditions in India. Hopefully, the above discourse on the topic will help UPSC exam aspirants prepare well. They can also refer to extensive study materials and seek expert guidance for all-around preparation.

Other Related Links

NCERT Notes: Geography Notes Geography and International Relations through Maps
Previous Year UPSC Prelims Geography Questions With Solutions Geography Questions in UPSC Mains GS 1
Geography Questions and Answers for UPSC Topic-Wise GS 1 Questions for UPSC Mains

Frequently Asked Questions on Air Mass


What are superior air masses?

These occur when the dry air is formed by the downward motion of the atmosphere.


What is a weather front?

Fronts are the boundaries that separate air masses from one another.


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