Causes of the South Subtropical Monsoon Climate

The cause of South Asian winter monsoon: the difference of thermal properties between land and sea leads to the difference of air pressure between ocean and South Asian continent. The northeast wind blows from the inland, and the climate is characterized by high temperature and little rain. The cause of the South Asian summer monsoon: the wind belt of the pressure belt moves with the seasons, and the climate is characterized by hot and humid.

Causes of the South Subtropical Monsoon Winter: Due to the different specific heat capacities of land and sea between Asia and Europe and the Pacific Ocean, the continental temperature is low, the air contracts and sinks, and the air pressure rises. Especially in Mongolia-Siberia region at high latitude, a strong high pressure center appeared. On the ocean, on the contrary, there is a pressure difference between the land and the ocean. Under the action of horizontal pressure gradient force, the wind blows from land to sea (the air flow on the same horizontal plane always blows from high pressure to low pressure, and the force that pushes the horizontal air flow from high pressure to low pressure is called horizontal pressure gradient force). However, under the action of the geostrophic deflector, the wind does not blow directly to the ocean, but constantly deflects to the right.

Therefore, the whole east coast of Eurasia is controlled by the north wind in winter, because the north wind blows from the high-latitude continent in winter, so it is cold and dry. The real north wind has turned to the northeast wind when it reaches South Asia. Moreover, the northern part of South Asia is blocked by mountains and the terrain is blocked. Winter is located on the leeward slope, and the winter wind has the effect of burning wind, which becomes high temperature and dry. In addition, its latitude is low, and the height of the sun is actually high in winter, so the temperature is high in winter and there is little rain.

Summer: The southeast wind, which should have appeared in the southern hemisphere, expanded its control area to the northern hemisphere as the direct point of the sun moved northward. At this time, due to the different thermal properties of land and sea, a low pressure center appeared near South Asia, and the southeast trade winds continued to move northward. However, due to the geostrophic bias in the northern hemisphere, the direction of the southeast trade wind changed to the southwest wind. The southwest monsoon is actually blown from the low-latitude ocean, so it controls the hot and rainy weather in South Asia.

The causes of tropical monsoon climate are mainly distributed in the South Asian subcontinent and the northern part of Indo-China Peninsula, which are related to the huge thermal gap between land and sea and the seasonal movement of the pressure zone.

In winter, there is a strong cold high in the Asian continent, which is the Mongolian high, while the Indian subcontinent and Indochina Peninsula are at the bottom of the Mongolian high. In winter, the cold source of the Qinghai-Tibet Plateau promotes the formation of the northeast monsoon.

In summer, there is a low pressure near thar desert, India, which is the Indian low pressure, while the Indian subcontinent has a southwest wind at the front and bottom of the low pressure. Combined with the summer heat source of the Qinghai-Tibet Plateau and the northward movement of the equatorial low pressure belt, the southeast trade wind from the southern hemisphere crosses the equator and becomes the southwest monsoon formed by the thermal action of land and sea, forming the strongest monsoon southwest monsoon in South Asia and Southeast Asia.