What is the cause of the summer monsoon in China?

Most of China is located in the north temperate zone, with mild climate and distinct seasons, which is suitable for human habitation and survival. Continental monsoon climate is the main feature of China climate. From September every year to April the following year, a dry and cold winter wind blows from Siberia and Mongolia Plateau, which is cold and dry, with a great temperature difference between the north and the south. From April to September every year, a warm and humid summer monsoon blows from the eastern and southern seas, which is generally hot and rainy, and the temperature difference between north and south is very small. China is divided into six temperature zones from south to north: equatorial zone, tropical zone, subtropical zone, warm temperate zone, temperate zone and cold temperate zone. The precipitation gradually decreases from southeast to northwest, and the annual average precipitation varies greatly from place to place, reaching more than 1500mm in the southeast coast and less than 200mm in the northwest inland.

cause

As for the cause of monsoon, some people think that it is caused by the thermal difference between land and sea and the seasonal variation of this difference; Others believe that it is caused by the seasonal displacement of the planetary wind belt. Some climatologists in China believe that the monsoon phenomenon is a comprehensive phenomenon under the influence of three factors: the thermal effect of land and sea distribution, the seasonal variation of atmospheric circulation and the specific terrain. For example, the Indian monsoon is particularly remarkable and stable because the seasonal changes of the monsoon caused by the land and sea distribution are exactly the same as those of the planetary wind belt. In winter, India is located in the south of cold high pressure and in the trade wind zone, so the northeast monsoon in India is particularly stable; In summer, India is located in the south of the thermal depression. When the equatorial trough moves northward, the southwest wind will pass through it. So the southwest monsoon is particularly stable.

Asia is located in the east of Asia-Europe continent, the largest continent on the earth, close to the Pacific Ocean and the Indian Ocean. Coupled with the seasonal variation of planetary circulation in the upper air and the topography of the Qinghai-Tibet Plateau, it forms a unique monsoon circulation system in Asia. The thermal difference between land and sea in winter and summer causes the seasonal changes of the atmospheric activity centers (i.e. high and low pressure activity centers) between land and sea, and makes the monsoon wind direction change regularly.

In winter, the radiation on the Asian land cools rapidly, forming a dry and cold Siberian high (also known as Mongolian high) and a cold and wet Aleutian low in the North Pacific. Both are very developed, especially the former is very powerful and almost controls the whole Asian continent. It is the center of continental anticyclone and the source of dry and cold polar continental air mass, and also the source of continental monsoon in winter. Because the subtropical high and the continental high are linked together in winter, they are powerful and become the dominant climate in the Asian continent in winter and half a year. High-pressure dry and cold air flows outward. In winter, northwest wind prevails along the Pacific coast and northeast wind prevails along the Indian Ocean coast. This is the winter wind in East Asia and South Asia, with the characteristics of sunny, cold and dry winter high-pressure weather. Winter wind is a dry land wind, which is generally not easy to rain, but it can form a blizzard when it blows to the northwest of Japan. The warm sea invading Jiangnan metamorphic polar continental air mass can form cloudy and warm weather in winter and spring or rainy weather. In winter, the Qinghai-Tibet Plateau blocks the westerly airflow and divides it into two branches, forming a circulation situation in the southern trough of the northern ridge. Because of the existence of the high-pressure ridge in the northern plateau, it is very beneficial to the southward movement of the winter monsoon, which strengthens the influence of the winter monsoon and causes the winter climate in China to be cold. The low pressure trough in the south of the plateau has a great influence on the weather and climate in the south of China because of the large amount of warm and humid air flow in front of the trough. Due to the blocking of the plateau, the southern Xinjiang and Hexi areas on the north side of the plateau are dry and cold in winter; There is little cold air activity in India and Myanmar in the south, and it is dry and warm in winter. In winter, the Qinghai-Tibet Plateau is a cold source, which will strengthen the downdraft near the plateau, thus strengthening the winter monsoon circulation.

In summer, the Asian continent is controlled by the heating depression, and its center is in northwest India, southern Iran and Arabian Peninsula, and it is integrated with the equatorial depression. At this time, the Hawaiian high extends westward and pushes northward, with the strongest force and the largest range, thus forming the southeast monsoon blowing from the western edge of the North Pacific high to the eastern part of Asia. This is the East Asian summer monsoon, which is a warm and humid air flow originating from tropical ocean air mass, and has the greatest influence on the Asian continent in summer. In South Asia, at this time, due to the northward shift of the planetary wind belt, the equatorial depression moved to the northern hemisphere, and the southeast trade winds in the southern hemisphere turned into southwest winds after crossing the equator. This is the summer monsoon in South Asia. When the southwest monsoon reached the Bay of Bengal and advanced northward, it was blocked by the Qinghai-Tibet Plateau and divided into two branches: one along the Himalayas to the west, thus maintaining the thermal depression in northwest India; The other branch flows to China along the mountain range, expanding the influence of southwest monsoon on China. The Qinghai-Tibet Plateau is the heat source of the surrounding free atmosphere in summer, which will inevitably strengthen the monsoon depression near the plateau, thus playing a role in strengthening the summer monsoon.

Responder: Painter-Juren Level 4 3- 17 16:39

monsoon climate

Monsoon climate is a mixture of continental climate and maritime climate. Summer is affected by the warm and humid air current in the ocean, which is hot, humid and rainy, and the climate is maritime. In winter, affected by the dry and cold air currents in the mainland, the climate is cold, dry and rainy, which belongs to the continental climate.

In monsoon climate, it is warm in summer and cold in winter. Therefore, the annual temperature is higher than that of the ocean. The month of 1 appears in Leng Yue, showing the characteristics of continental climate. The hottest month appears in July and August, and the temperature in autumn is higher than that in spring, showing maritime climate characteristics. For example, the annual variation of temperature in Changsha is 24.6℃, the average temperature in Leng Yue is 4.7℃ in June and 65438+ 10, and the hottest month is July-August. From the monthly average, the average temperature in July is 29.3℃, and that in August is 28.7℃, only 0.6℃ higher than that in August. In fact, in the 30 years from 195 1 to 1980, the average temperature was higher in 1/3 years than in July. Taking Nanjing as an example, the annual variation is 26.0℃, 65,438+10, the coldest in October, with an average of 2.0℃, the hottest in July and August, with an average of 28.0℃ in July and 27.8℃ in August,1951~1.

In monsoon climate, it is wet and rainy in summer and dry and rainy in winter. For example, the annual precipitation in Changsha is 1390 mm, accounting for 71%from March to August; The annual precipitation in Nanjing is 103 1mm, accounting for 74% from April to September. Under the monsoon climate, the amount of precipitation and the time of rainy season depend entirely on the time and intensity of monsoon advance and retreat. For example, the rainy season in Changsha is one month earlier than that in Nanjing. In northern China, the rainy season only lasts from June to August, even from July to August. The length of rainy season is related to the control of summer monsoon. In monsoon climate, rainfall is extremely unstable and varies greatly every year. In Changsha, the rainfall in rainy years is twice that in dry years, three times that in Nanjing and five times that in Beijing. Therefore, in the monsoon climate, frequent floods and droughts are extremely unfavorable to people's production and life.

The high temperature in monsoon climate is basically the same as that in rainy season. Although it is inevitably sultry, it is very beneficial to the development of agriculture. Because the crops are growing vigorously, when water is most needed, the rainwater supply is sufficient.