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For the band Monsoon see Sheila Chandra.

A monsoon is a (wind) pattern that reverses direction on a seasonal basis. The term was originally applied to monsoonal winds in the Arabian Sea and Indian Ocean. The word is also used to label the season in which this wind blows from the southwest in India and adjacent areas that is characterized by very heavy rainfall, and specifically the rainfall that is associated with this wind.

In terms of total precipitation, total area covered and the total number of people affected, the monsoons affecting the Indian Subcontinent dwarf the so-called North American monsoon.

History

Monsoon is derived from the Arabic word "موسم" (mausem), which means season. In English, the term was borrowed more directly from the Portuguese, monção, and possibly via early modern Dutch, monson. The term arose in the 16th century during the rise in navigation across the Indian Ocean, because the monsoonal winds were so critical to sailing:

In Goa they stayed till the Monson, or time of the windes came in to sayle for China. 1598 W. PHILIP tr. J. H. van Linschoten Disc. Voy. E. & W. Indies I. xcii. 143/1.

It is most often applied to the seasonal reversals of the wind direction along the shores of the Indian Ocean, especially in the Arabian Sea, that blow from the southwest during one half of the year and from the northeast during the other.

The monsoon is very relevant to the people of South India, especially the people of Kerala state. But environmental degradation has weakened or changed the monsoon system prevalent for many centuries.

Processes

Monsoons are caused by the fact that land heats up and cools down more quickly than water, owing to the difference in their specific heat. Thus, in summer, land reaches a higher temperature than the ocean. The hot air over the land tends to rise, creating an area of low pressure. This creates an extremely constant wind blowing toward the land. Associated rainfall is caused by the moist ocean air being diverted upward by mountains, which causes cooling, and in turn, condensation.

In winter, the land cools off quickly, but the ocean retains heat longer. The hot air over the ocean rises, creating a low pressure area and a breeze from land to ocean. Because the temperature difference between the ocean and land is less than in summer, the winter monsoon wind is not as constant.

Monsoons are similar to sea breezes, but they are much larger in scale, stronger, and are more constant.

Monsoon systems

As monsoons have become better understood, the definition has been broadened to include almost all of the phenomena associated with the annual weather cycle within the tropical and subtropical continents of Asia, Australia, and Africa, and the adjacent seas and oceans. It is within these regions that the most vigorous and dramatic cycles of weather events on Earth take place.

Even more broadly, it is now understood that in the geological past, monsoon systems must have always accompanied the formation of supercontinents such as Pangea, with their extreme continental climates.

Northeast Winter Monsoon (Asia)

In Asia, the northeastern winter monsoons take place from December to early March. The temperature over central Asia is lower, creating a zone of high pressure there. The jet stream in this region splits into the southern subtropical jet and the polar jet. The subtropical flow directs northeasterly winds to blow across south Asia, creating dry air streams which produce clear skies over India from the months of November to May.

Meanwhile, a low pressure system develops over northern Australia and winds are directed toward Australia.

During the Northeast Winter Monsoon, Australia and southeast Asia receive la