Discuss the concept of air mass and explain its role in macro-climatic changes. (UPSC 2016)

An air mass is a vast body of air, extending over thousands of square kilometres, with fairly uniform temperature and moisture. It forms over a source region such as oceans, deserts or ice sheets, where light winds allow it to take on surface characteristics.

• Types: It may be maritime or continental, and tropical, polar or arctic in origin.
• Modification: While moving, it changes through heating, cooling, evaporation and mixing with other air masses.
• Macro-climatic role: Air masses transfer heat and moisture from low to high latitudes, shaping broad climate belts.
• Fronts and storms: Meeting of different air masses creates fronts, which generate mid-latitude cyclones and rainfall.
• Seasonal shifts: Their movement helps explain monsoons, heat waves, cold waves and dry or wet spells.

Thus, air masses are major controls of regional climate. Their dominance, movement and interaction explain large-scale climatic variations across the globe.