Air Mass | Air masses based on Source Regions

PMF IAS Current Affairs

Air Masses

  • When the air remains over a homogenous area for a sufficiently longer time, it acquires the characteristics of the area. The homogenous regions can be the vast ocean surface or vast plains and plateaus.
  • The air with distinctive characteristics in terms of temperature and humidity is called an air mass. It is a large body of air having little horizontal variation in temperature and moisture.
  • Air masses form an integral part of the global planetary wind system. Therefore, they are associated with one or other wind belt.
  • They extend from surface to lower stratosphere and are across thousands of kilometers.

Source regions

  • The homogenous surfaces, over which air masses form, are called the source regions.
  • The main source regions are the high pressure belts in the sub tropics (giving rise to tropical air masses) and around the poles (the source for polar air masses).
  • Source Region establishes heat and moisture equilibrium with the overlying air mass.
  • When an air mass moves away from a source region, the upper level maintains the physical characteristics for a longer period. This is possible because air masses are stable with stagnant air which do not facilitate convection. Conduction and radiation in such stagnant air is not effective.

Conditions for the formation of Air masses

  • Source region should be extensive with gentle, divergent air circulation (slightly at high pressure).

convergence - divergence - cyclonic-anticyclonic (Custom)

  • Areas with high pressure but little pressure difference or pressure gradient are ideal source regions.
  • There are no major source regions in the mid-latitudes as these regions are dominated by cyclonic and other disturbances.

Air masses based on Source Regions

  • There are five major source regions. These are:
  1. Warm tropical and subtropical oceans;
  2. The subtropical hot deserts;
  3. The relatively cold high latitude oceans;
  4. The very cold snow covered continents in high latitudes;
  5. Permanently ice covered continents in the Arctic and Antarctica.
  • Accordingly, following types of airmasses are recognised:
  1. Maritime tropical (mT);
  2. Continental tropical (cT);
  3. Maritime polar (mP);
  4. Continental polar (cP);
  5. Continental arctic (cA).
  • Tropical air masses are warm and polar air masses are cold.
  • The heat transfer processes that warms or cools the air takes place slowly.

Air masses -Source Regions

Cold Air Mass

  • A cold air mass is one which is colder than the underlying surface and is associated with instability and atmospheric turbulence.

Cold source regions (polar air masses)

  • Arctic Ocean – cold and moist
  • Siberia – cold and dry
  • Northern Canada – cold and dry
  • Southern Ocean – cold and moist

Warm Air Mass

  • A warm air mass is one which is warmer than the underlying surface and is associated with stable weather conditions.

Warm source regions (tropical air masses)

  • Sahara Desert – warm and dry
  • Tropical Oceans – warm and moist

Influence of Air Masses on World Weather

  • The properties of an air mass which influence the accompanying weather are vertical distribution temperature (indicating its stability and coldness or warmness) and the moisture content.
  • The air masses carry atmospheric moisture from oceans to continents and cause precipitation over landmasses.
  • They transport latent heat, thus removing the latitudinal heat balance.
  • Most of the migratory atmospheric disturbances such as cyclones and storms originate at the contact zone between different air masses and the weather associated with these disturbances is determined by characteristics of the air masses involved.

Classification of Air Masses

  • Broadly, the air masses are classified into polar and tropical air masses.
  • Both the polar and the continental air masses can be either of maritime or continental types.

Continental Polar Air Masses (CP)

  • Source regions of these air masses are the Arctic basin, northern North America, Eurasia and Antarctica.
  • These air masses are characterized by dry, cold and stable conditions.
  • The weather during winter is frigid, clear and stable.
  • During summer, the weather is less stable with lesser prevalence of anticyclonic winds, warmer landmasses and lesser snow.

Maritime Polar Air Masses (MP)

  • The source region of these air masses are the oceans between 40° and 60° latitudes.
  • These are actually those continental polar air masses which have moved over the warmer oceans, got heated up and have collected moisture.
  • The conditions over the source regions are cool, moist and unstable. These are the regions which cannot lie stagnant for long.
  • The weather during winters is characterized by high humidity, overcast skies and occasional fog and precipitation.
  • During summer, the weather is clear, fair and stable.

Continental Tropical Air Masses (CT)

  • The source-regions of the air masses include tropical and sub-tropical deserts of Sahara in Africa, and of West Asia and Australia.
  • These air masses are dry, hot and stable and do not extend beyond the source.
  • They are dry throughout the year.

Maritime Tropical Air Masses (MT)

  • The source regions of these air masses include the oceans in tropics and sub-tropics such as Mexican Gulf, the Pacific and the Atlantic oceans.
  • These air masses are warm, humid and unstable.
  • The weather during winter has mild temperatures, overcast skies with fog.
  • During summer, the weather is characterized by high temperatures, high humidity, cumulous clouds and convectional rainfall.

Primary References: NCERT Geography, Spectrum’s Geography [Amazon and Flipkart], and Savindra Singh [Amazon and Flipkart]

Sharing is Caring !!

Newsletter Updates

Subscribe to our newsletter and never miss an important update!

Assured Discounts on our New Products!


  1. is it true that unstability is determined by following factors–
    1)presence of humidity
    2)heavier air overlies lighter air
    as you have given that maritime air mass will be unstable

  2. does continental polar air mass is colder air mass then what is the reason for it being stable?
    similarly as the case of continental tropical air mass

  3. Because these airmass originate on continent,are usually dry.Due to dry condition rainfall not occur.That is why it is considered as stable

Leave a Reply

Your email address will not be published. Required fields are marked *

The downloads are available to only those members that have purchased

July 2023 to December 2024 Current Affairs


July 2023 to December 2023 Current Affairs

Already purchased? Log in to download.

Subscriber Discounts

Active SubscriptionRenewal DiscountDiscount on 2024 Current AffairsDiscount on 2023 2nd Half Current Affairs
Geography30%NA NA
EnvironmentNA NA
AgricultureNA NA
ScienceNA NA
Current Affairs (Old)NANA NA

These discounts are auto-applied to the respective Product Price based on your active subscriptions.

Your Active Plans

Looks like you dont have any downloads yet! Subscribe!

Year(s) = Validity of the Downloads

The validity of the Current Affairs Course is from July 2023 to December 2024 (18 months).

For the rest of the products, the validity is as follows:

1 Year Validity == Validity of the Download links (both Static & the Subject Related Current Affairs) is 1 Year from the date of purchase.

2 Years Validity == Validity of the Download links (both Static & the Subject Related Current Affairs) is 2 Years from the date of purchase.

We strongly recommend a 2 Year Plan as the UPSC Cycle lasts for close to 2 Years.

For example,

If you purchase the notes with “Download Validity == 1 Year,” on 28/09/2023, then you will be able to download the Static & the Subject Related Current Affairs files till 28/09/2024.

If you purchase the notes with “Download Validity == 2 Years,” on 28/09/2023, then you will be able to download the Static & the Subject Related Current Affairs files till 29/09/2025.

If we bring out the Updated (New) Editions of the Static Files within your subscription period, you will be able to download them without paying anything extra.

Irrespective of the package you choose, Current Affairs of Geography, Environment, Sci & Tech and Indian Agriculture are available from Jan 2023.

Current Affairs of 2022 & earlier are available for free on PMF IAS Google Drive Folder.

Once the payment is made, you need to log in to the Downloads Page to download the files (check your email for the login details).


Subscribe to our newsletter and never miss an important update!