The southwest monsoon prevails in South Asia andSoutheast AsiaThe Indian summer monsoon is the most typical summer monsoon in the region.The southeast trade wind from the Indian Ocean, after crossing the equator, turns to the southwest under the influence of the deflection force of the earth's rotation, passes through the tropical ocean and carries a lot of water vapor, which is the main source of precipitation in the Indian Peninsula and Southeast Asia.To the east through the Indian Peninsula and the Bay of Bengal, it can affect southern China;When the southwest monsoon develops strongly, it can also penetrate into the Yangtze River basin.[1]
The southwest monsoon, the summer monsoon prevailing in South Asia and Southeast Asia, is most typical of the Indian summer monsoon.The southeast trade wind from the Indian Ocean, after crossing the equator, turns to the southwest under the influence of the deflection force of the earth's rotation, passes through the tropical ocean and carries a lot of water vapor, which is the main source of precipitation in the Indian Peninsula and Southeast Asia.To the east through the Indian Peninsula and the Bay of Bengal, it can affect southern China;When the southwest monsoon develops strongly, it can also penetrate into the Yangtze River basin.[1]
Formation and characteristics
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formation
The monsoon in southern Asia is mainly caused byTrade wind beltCaused by seasonal movement ofThermal difference between land and seaToIndian monsoonFor example, the trade wind belt moves southward in winter,Equatorial depressionMoving to the southern hemisphere, the cold high over the Asian continent is strong, and the northeast wind in the south of the high becomes the winter wind in southern Asia.In summer, the trade wind belt moves northward, and the equatorial depression moves to the northern hemisphere,Low voltage centerAppears inIndian subcontinent。This is the winter in the southern hemisphere. Australia is a region of low temperature and high pressure,Barometric gradientFrom south to north, the southward air flows across the equatorcoriolis force And form southwest wind, which is theSummer monsoon。
Under the influence of the monsoon, South Asia is also dry in winter and wet in summer, but there is a clear difference between it and the East Asian monsoon, that is, the South Asian summer monsoon is stronger than the winter monsoon.This is because southern Asia is far away from Mongolia in winter-SiberiaThe high pressure center is blocked by the Tibetan Plateau. In addition, the Indian Peninsula is small in area and latitude, and the pressure gradient between land and sea is weak, so the winter monsoon is not strong.On the contrary, the temperature of the Indian Peninsula is particularly high in summer, which is the center of the thermal depression. The pressure gradient between the Indian Peninsula and the subtropical high in the southern hemisphere is large, so the summer monsoon in South Asia is stronger than the winter monsoon.[2]
characteristic
(1) The characteristic periods of southwest monsoon change are mainly 41 ka and 23 ka periods;
(2) The south-west monsoon water vapor transport is mainly zonal;
(3) The main prevailing wind direction is southwest wind, which is characterized by obvious crisscross of rainy season and dry season;
(4) The southwest monsoon belongs to the tropical monsoon, and the main area of the southwest monsoon is located at 030。N is a monsoon system with strong summer monsoon force, which is characterized by high annual temperature, and has little relationship with mid high latitude circulation and its associated cold air activities.[3]
Scope of influence
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For a long time, the influence area of southeast monsoon and southwest monsoon is generally considered to be divided into the southeast monsoon climate area formed by the southeast warm and humid air flow from the North Bay of the Western Pacific Ocean, the southwest monsoon climate area formed by the southwest warm and humid air flow from the Bay of Bengal in the Indian Ocean, or the multi-year average position of Kunming quasi stationary peak as the boundary,The west is the southwest monsoon region, which is also the Indian tropical monsoon region, and the east is the southeast monsoon region. However, in the recent study, this boundary will be re confirmed: the water vapor convergence zone of the Pacific Ocean and the Indian Ocean is located in East Asia, which reaches 97.50E in the west and 142.50E in the east.In the water vapor convergence area of the Indian Ocean and the Pacific Ocean in summer, the net water vapor contribution rate of the Pacific Ocean gradually decreases from west to north;The spatial variation of the net water vapor contribution rate in the Indian Ocean is more complex than that in the Pacific Ocean, but it tends to decrease from east to north;Among them, the water vapor in the typical longitudinal range valley area in Yunnan Province, which is characterized by longitudinal mountains and rivers, mainly comes from the Indian Ocean.It is found that the contribution rate of net water vapor in the Indian Ocean is far greater than that in the Pacific Ocean in June and July in Yunnan, which is still mainly affected by the southwest monsoon.In August, the contribution rate of Pacific net water vapor in Yunnan region gradually exceeded that of Indian Ocean, and the influence of southeast monsoon gradually strengthened.[3]
