Discuss the concept of air mass and explain its role in macro-climatic changes.
Concept of air mass:
An air mass is a large body of air in the lower atmosphere that has similar temperature and moisture properties. Air masses are typically areas of relatively uniform surface tracts of ocean, desert, or snow-covered plains which experience weak winds and stable conditions that allow the atmosphere to assume physical characteristics from the underlying water or land. Air masses are defined according to both their region of origin and the course traveled.
Air masses based on Source Regions
There are five major source regions these are
- Warm tropical and subtropical oceans,
- subtropical hot deserts,
- relatively cold high latitude oceans,
- The very cold snow-covered continents in high latitudes,
- and Permanently ice-covered continents in the Arctic and Antarctica.
Tropical air masses are warm and polar air masses are cold. The heat transfer process that warms or cools the air takes place slowly. The climates of most regions worldwide are affected by air masses.
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.
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.
Maritime Tropical Air Masses (MT) – The source regions of these air masses include the oceans in the tropics and sub-tropics such as Mexican Gulf, the Pacific, and the Atlantic oceans. These air masses are warm, humid, and unstable.
Maritime Polar Air Masses (MP) – The source region of these air masses is the oceans between 40° and 60° latitudes. These are actually those continental polar air masses that have moved over the warmer oceans, got heated up, and collected moisture. The conditions over the source regions are cool, moist, and unstable. These are the regions that cannot lie stagnant for long.
Therefore Air masses play an important role in microclimatic changes, especially in temperate latitudes.