What are the characteristics of monsoon?

Monsoon is a large-scale convection phenomenon with a period of one year, which is caused by land and sea distribution, atmospheric circulation, continental topography and other factors. Asia is the most famous monsoon region in the world, and its monsoon characteristics are mainly manifested in the existence of two main monsoon circulations, namely, the northeast monsoon prevailing in winter and the southwest monsoon prevailing in summer, and their transformation has an explosive mutation process with a short transition period. Generally speaking, 1 1 is the winter monsoon period, June-September is the summer monsoon period, and April-May and 10 are the transition periods between summer monsoon and winter monsoon. However, the seasonal differences in different regions are different, so the division of monsoon is not completely consistent.

Monsoon is a widely prevailing wind system, and the wind direction changes significantly with the seasons. Like the wind belt, it belongs to the planetary circulation system, and its formation is caused by the temperature difference between the ocean and the land in winter and summer. Summer monsoon blows from the ocean to the mainland, and winter monsoon blows from the mainland to the ocean.

Monsoon has a wide range of activities, affecting the area of 1/4 on the earth and the life of 1/2 people. Western Pacific, South Asia, East Asia, Africa and northern Australia are all areas with obvious monsoon activities, especially Indian monsoon and East Asian monsoon. There is also a small monsoon region along the Pacific coast of Central America, while there is no obvious monsoon region in Europe and North America, only some monsoon trends and phenomena appear.

In winter, the temperature of the mainland is lower than that of the adjacent ocean. There is a cold high pressure on the mainland and a corresponding low pressure on the ocean, and the airflow blows from the mainland to the ocean in a large range, forming a winter wind. Winter winds prevail in the northern hemisphere, especially on the east coast of Asia. The northbound monsoon extends from the mid-latitude to the equatorial region. This monsoon originated from Siberian cold high, and in the process of its southward eruption, it produced strong northerly winds and northeast winds in East and South Asia. In Africa and the Bay of Bengal, there is also an obvious northeast wind blowing near the equator. Although there are winter winds in the East Pacific and South America, they are not as obvious as those in Asia.

In summer, the ocean temperature is relatively low, the mainland temperature is high, and the ocean appears high pressure or the original high pressure is strengthened, and the mainland appears thermal low pressure; At this time, southwest and southeast monsoons prevail in the northern hemisphere, especially in the Indian Ocean and South Asia. Most of the southwest monsoon originated in the South Indian Ocean, crossed the equator on the east coast of Africa, reached South Asia and East Asia, and even reached central China and Japan. The other part of the southeast wind mainly comes from the northwest Pacific, and the southerly or southeast wind affects the eastern coast of China.

Summer monsoon generally goes through four stages: outbreak, activity, interruption and regression. The East Asian monsoon broke out the earliest, starting in early May, advancing from southeast to northwest, and stabilizing in late July. Usually retreat begins in mid-September, and the path is opposite to that when advancing. Under the counterattack of the northerly airflow, it gradually retreated from northwest to southeast.