A question about geography ---- What is monsoon?

Monsoon is a large-scale convective phenomenon caused by the distribution of land and sea, atmospheric circulation, large terrain and other factors, with a yearly cycle. The Asian region is the world's most famous monsoon area, which is characterized by the prevalence of the northeast monsoon in winter and the southwest monsoon in summer. Their transition has a violent and abrupt process with a short transition period in between. Generally speaking, from November to March of the following year is the winter wind period, June to September is the summer wind period, and April, May and October are the transition period between summer and winter winds. Seasonal differences vary from region to region, and thus the division of the monsoon is not consistent.

The east-west wind belts that surround the globe are not all seamless and intact, but show a marked discontinuity. In the tropical, subtropical, and temperate regions of the equatorial windless, trade wind, subtropical windless, and westerly zones, some areas are completely replaced by north-south oriented monsoons.

The monsoon is a wide range of prevalent, significant changes in wind direction with the seasons of the wind system, and the same as the wind belt is a planetary-scale circulation system, its formation is caused by the winter and summer ocean and land temperature differences. Monsoon in the summer from the ocean to the continent, in the winter from the continent to the ocean.

Monsoon activity range is very wide, it affects the earth 1/4 of the area and 1/2 of the population's life. The western Pacific Ocean, South Asia, East Asia, Africa and northern Australia, are the monsoon activity is obvious areas, especially the Indian monsoon and East Asian monsoon is the most significant. The Pacific coast of Central America also has a small monsoon area, while Europe and North America have no obvious monsoon area, only some monsoon trends and monsoon phenomena.

In winter, the continental temperature is lower than the neighboring ocean temperature, the continent appears cold high-pressure, the corresponding low pressure on the ocean, the air current is widely blown from the continent to the ocean, the formation of the winter monsoon. Winter monsoon in the northern hemisphere prevails north or northeast wind, especially along the eastern coast of Asia, northward monsoon from mid-latitude has been extended to the equatorial region, this monsoon originated in the Siberian cold high-pressure, it is in the process of outbursts to the south, its East Asia and South Asia to produce a very strong north and northeasterly winds. Africa and the Bay of Bengal region also have significant northeast winds blowing to the near-equatorial region. Winter winds occur in the eastern Pacific and South America, but they are not as significant as in Asia.

Summer, the ocean temperature is relatively low, the continent is warmer, the ocean appears high pressure or original high pressure to strengthen the continent appears hot low pressure; this time the northern hemisphere prevails in the southwestern and southeastern monsoon, especially in the Indian Ocean and the South Asian region is the most significant. Most of the southwest monsoon originates from the South Indian Ocean, in the east coast of Africa across the equator to reach South Asia and East Asia, and even reach China's central China and Japan; another part of the southeast wind mainly from the Northwest Pacific Ocean, south or southeast of the form of impact on the eastern coast of China.

Summer winds generally experience four stages: outbreak, active, interruption and retreat. The earliest outbreak of the monsoon in East Asia begins in early May, advancing from southeast to northwest, stabilizing in late July, and usually beginning to retreat in mid-September, with the path reversed from the advance and retreating from northwest to southeast under the counterattack of the northerly flow.

The summer winds affecting our country originate from three air currents: first, the Indian summer winds, when the Indian monsoon moves northward, the southwest monsoon can penetrate deep into our continent; second, the trans-equatorial air currents flowing through Southeast Asia and the South China Sea, which is a low-altitude southwesterly air current; and, third, the southeasterly monsoon coming from the west side of the subtropical high pressure of the northwestern Pacific Ocean, which sometimes turns to the south or southwesterly air currents.

The monsoon begins to appear in the northern part of the South China Sea in early May each year, after three sudden northward thrusts and four stationary phases in between, arriving in northern South China from late May to June 5-10, arriving in the Yangtze River Basin from late June to early July, advancing to the Yellow River Basin in mid- to 20 July, and moving northward to the final boundary from late July to August 10 before the end of the month -around northern China. China's winter winds are stronger than summer winds, especially on the east coast, often more than 8 north to northwest winds accompanied by a cold wave south; the South China Sea is dominated by northeasterly winds, the number of gales is less than in the north.

The monsoon region enjoys a unique climate, where most of the precipitation comes from the period of prevailing summer winds. In ancient times, China utilized the monsoon to carry out navigation activities and made brilliant achievements. The Ming dynasty Zheng He to the West, in addition to the first summer sailed back in the fall, the remaining six are in the winter half of the northeast monsoon period set off in the southwest monsoon during the return voyage. This fully demonstrates that the ancients already had a profound understanding of the law of wind activity.

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