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Day 63 – Q 3. What is an air mass? How does it get formed? In what ways does it affect the local climate conditions? Discuss.

3. What is an air mass? How does it get formed? In what ways does it affect the local climate conditions? Discuss. 

वायु राशि क्या है? यह कैसे बनता है? किन तरीकों से यह स्थानीय जलवायु परिस्थितियों को प्रभावित करता है? चर्चा करें।


An air mass is a large volume of air in the atmosphere that is mostly uniform in temperature and moisture.


Formation of 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. The homogenous surfaces, over which air masses form, are called the source regions. An air mass acquires these attributes through heat and moisture exchanges with the surface.

Further, 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. 

Furthermore, Uneven warming and cooling of the earth’s surface by the Sun gives rise to air masses. Air Masses are most common in the tropics, subtropics and high latitudes. The zones from which air masses grow are called “source regions” which are the large surfaces with uniform temperatures and humidity.  These are generally tracts of ocean, desert or snow-covered plains. For instance,

  • The warm air masses form over the equator or desert areas where the solar radiation is maximum. In clear, almost cloudless days, the heat is reflected back to the atmosphere. The air becomes light and spreads.
  • Cold air masses form near the poles where solar radiation is at a minimum. On cloudless days, the snow cover near the Poles, reflect sunlight away, preventing the earth to warm up. When this persists for a long period of time, cold air masses form over a large area.
TLP Phase 1 – Day 63 Synopsis

TLP Phase 1 – Day 63 Synopsis

(Use a simple diagram depicting airmass in the exam)

Air masses affecting local weather conditions:

In a particular area, the occurrence of particular air masses helps to ascertain the climate of that region. This in turn decides the type of flora and fauna as well as the type of crops that can be grown. For instance, 

  • Precipitation: E.g. the maritime-tropical air over Atlantic Ocean, Caribbean Sea is a major reason for precipitation east of Rocky Mountains. It is also the cause of persistent humidity in the summer season.
  • Temperature: Maritime polar air affects the coastal temperature in subtropical and arctic regions.
  • Cyclones and anti-cyclones: Stormy cyclones form near the air-mass fronts. The mixing of air masses will result in rising air feeding the cyclone formations in the subtropical cyclone. Similarly, the warm maritime tropical air mass will provide the energy for tropical cyclones.
  • Drought: they are the result of hot, dry air mass. This can destroy natural vegetation and kill trees. These regions have the increase risk of devastating wildfires. E.g. California wild fires.
  • At the boundaries between air masses, the clash of masses of air with different characteristics can lead to dynamic weather like hail, tornadoes, high winds or ice storms. E.g. tropical cyclones formed in east china sea.


Air masses spread across massive region up to 1600 km or more. They exercise a considerable influence on the climatic conditions of the region over which they lodge and carry with them distinctive climatic features of their source region. 

Additional information (Per se not required in the answer as per the demand of the question):

The air masses are classified according to the source regions. There are five major source regions:

  • Warm tropical and subtropical oceans.
  • The subtropical hot deserts
  • The relatively cold high latitude oceans
  • The very cold snow-covered continents in high latitudes
  • Permanently ice-covered continents in the Arctic and Antarctica

Accordingly, the following air masses are formed.

  • Maritime tropical (mT): Maritime Tropical air mass results from the warm waters of the Gulf of Mexico and Gulf Stream. This air mass is characterized by hot, humid conditions.
  • Continental tropical (cT): These are the hot, dry air masses which originate over regions like northern Mexico and the southwestern United States.
  • Maritime polar (mP): Maritime Polar air masses have their source region over cold ocean currents or high latitude ocean waters. This air mass can produce widespread rain or snow, fog, drizzle, cloudy weather and long lasting light to moderate rain.
  • Continental polar (cP): Continental Polar air masses are cold to cool and dry. Continental Polar air masses form over Canada and Siberia. These air masses bring cold air during the winter and cool, relatively clear, rather pleasant weather in the summer.
  • Continental arctic (cA): This air mass is considered very cold. Their source of origin is Arctic Ocean, Siberia, Northern Canada, Southern Ocean.
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