Question – What do you understand by air mass ? Discuss its origin and how does it influence the world climate? – 2 December 2021
Answer – 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 across the surface of the Earth and can reach from ground level to the stratosphere into the atmosphere. They acquire identity by their humidity, origin and movement.
They are classified on the basis of-
- Latitudinal origination- Arctic, Tropical, Equatorial and Antarctic
- Continental air mass and Oceanic air mass
Origin 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.
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.
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 is formed.
Influence of air masses on the world climate:
- The air masses carry atmospheric moisture from oceans to continents causing precipitation over landmasses.
- Maritime polar air affects the coastal temperature in subtropical and arctic regions.
- 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.
- They cause arid conditions when dry air mass is present in a region causing desertification. This can destroy natural vegetation. These regions have the increase risk of devastating wildfires. E.g. California wild fires.
Thus, the vertical distribution of temperature in an air mass, and moisture content of the air are two basic properties of an air masses which control the weather conditions of the area affected by that air mass.