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[ m o n s o o n s   :   c a u s e s   o f   m o n s o o n s ]

Monsoons are an annually recurring weather phenomenon, triggered by the earth’s tilt in relation to the sun. Although they return every year, it is still impossible to tell the timing, duration, and quantity of rain each season, a fact that leaves impacted areas without accurate storm information. Monsoons are set by land and sea temperature differences. Land reflects the sun’s rays, heating air over land more rapidly. Water is able to absorb a lot of heat without itself changing temperature much, so air over water stays relatively cooler.

This fact is prevalent in Asia because the northern hemisphere has so much more land than the southern hemisphere, which is mostly ocean. During he summer, the earth is tilted at such an angle that the sun’s rays shine more directly on the northern hemisphere. The heat is absorbed by the land masses, warming the air above it. The hot air rises, and cooler ocean air rushes inland from the southern hemisphere to replace it. As it moves, it carries moisture with it, releasing it over land as the summer monsoon (also known as southwest monsoon). The cycle continues as the cooling air creates precipitation and releases more energy. This energy then heats the air, which rises and flows back to the sea, cools, descends, and rushes back to land to replace more warm, rising air. This monsoon is centered over continental Asia.

There is also a winter monsoon (also known as northeast monsoon), created during the winter when most of the sun’s rays shine on the southern hemisphere. During this season, the continents are cooler than the water, which retains absorbed heat. The air reverses circulation, with warm air rising over the oceans and cooler land air, called “cold surges,” rushing in to replace it. The cold surges pick up warm moisture as it travels across tropical waters only to release them over Indonesia, northern Australia, Sri Lanka, and the east Indian coast.

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