The reasons for the formation of monsoon climate.

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.

The Xia Feng that affects China comes from three air currents: one is the Indian summer monsoon. When the Indian monsoon moves northward, the southwest monsoon can go deep into Chinese mainland; Second, the cross-equatorial airflow flowing through Southeast Asia and the South China Sea belongs to the low-altitude southwest airflow; Thirdly, the southeast monsoon from the west side of the subtropical high in the northwest Pacific sometimes turns to the southerly or southwest airflow.

Monsoon begins to appear in the northern part of the South China Sea at the beginning of May every year, with three sudden northward pushes and four static stages in the middle. At the end of May to June 5- 10, it reached the northern part of South China, at the end of June to early July, it reached the Yangtze River valley, and from mid-July to 20th, it reached the northern boundary-North China. In China, the winter wind is stronger than the summer monsoon, especially in the eastern coastal areas, where there is often a north-northwest wind of magnitude 8 or above, accompanied by a cold wave. The south China sea is dominated by the northeast wind, and the number of strong winds is less than that in the north.

The monsoon region has a unique climate, and most of the precipitation comes from the prevailing summer monsoon. In ancient China, the use of monsoon to carry out navigation activities made brilliant achievements. Zheng He set sail for the first time in summer and returned in autumn in Ming Dynasty. The other six times set sail during the northeast monsoon in winter and returned during the southwest monsoon. This fully shows that the ancients had a profound understanding of the law of wind activity.

Due to the different degrees of heating and cooling between the mainland and the ocean in a year, the direction of a large range of winds between the mainland and the ocean changes regularly with the seasons, which is called monsoon. The most fundamental reason for the formation of monsoon is due to the different properties of the earth's surface and different thermal responses. Due to land and sea distribution, atmospheric circulation, large terrain and other factors, headwinds prevail in winter and summer with a one-year cycle.

[Edit this paragraph] Monsoon-Understanding

Monsoon has different names in ancient China, such as trade wind, yellowbird wind and plum blossom wind. In coastal areas, it is also called ocean wind. The so-called ocean wind is the southeast monsoon blowing from the southeast ocean to China in summer. Because ancient ships sailed mainly by wind, the northerly monsoon in winter was not conducive to the southern ships sailing to the mainland, and only the southerly wind in summer could make them reach the coast of China. Therefore, the southerly summer monsoon is also called the input wind. When the southeast monsoon reaches the middle and lower reaches of the Yangtze River in China, the rainy weather with regional climate characteristics ends and the summer drought begins. In Su Dongpo's poem "Ship Wind" in the Northern Song Dynasty, there is a sentence that "Huang Meiyu has broken three times and Wan Li has just come to ship wind". In the quotation of the poem, he explained: "Wuzhong (now southern Jiangsu) has had plum rains and the breeze is quiet;" At this age, the Lakers call it ship wind. The first time was the return of a sea ship, and the wind came from the sea and the ship to the cloud. The poem "Huang Meiyu", also called Meiyu, is a continuous rainy day in the middle and lower reaches of the Yangtze River from June to early July in the solar calendar. "Three o'clock" refers to the second half of the summer solstice, that is, early July. The plum rain mentioned in Su Dongpo's poems ended in early July, and the climate of the southeast monsoon is similar to the present climate.

Modern people's understanding of monsoon has made progress, and at least three points are recognized, namely:

Monsoon (1) is a phenomenon that the prevailing wind direction changes with the seasons in a large area. The emphasis on "large area" here is because the wind direction of a small area is greatly influenced by the terrain.

(2) With the change of wind direction, the nature of the control air mass also changes, such as the cold and dry air when the winter wind comes and the warm and humid air when the summer monsoon comes;

(3) With the change of prevailing wind direction, it will bring obvious weather and climate changes.

[Edit this paragraph] Monsoon formation

Monsoon is a kind of wind system with wide prevalence and obvious seasonal variation of wind direction. With the seasonal change of wind direction, the weather and climate also have obvious seasonal changes. The word "monsoon" comes from Arabic "mawsim", which means season. In ancient China, trade winds were called, which meant that the direction of this wind always changed with the seasons.

Englishman e Harley believes that monsoon is a large-scale direct circulation between land and sea with a period of one year due to the different thermal properties of land and sea and the seasonal variation of solar radiation. In winter, the mainland is colder than the ocean, there is cold high pressure on the mainland, and the near-surface air blows from the mainland to the ocean; In summer, the mainland is warmer than the ocean, hot and low pressure, and the near-surface air blows from the ocean to the mainland. Since 1950s, it has been pointed out that the seasonal displacement of planetary wind system is also a major cause of monsoon. In addition, not all areas with different land and sea have monsoon, and other physical factors play a role in the formation of monsoon. For example, the accumulation of heat and power in large terrain (such as Qinghai-Tibet Plateau) is difficult to return, and the air flow across the equator in the southern hemisphere has a great influence on the summer monsoon.

The main reason for the formation of monsoon is the seasonal variation of thermal circulation between land and sea. In summer, the heating of the mainland is stronger than that of the ocean, and the pressure changes slowly with the height above the ocean. So at a certain height, there is a horizontal pressure gradient from the mainland to the ocean, the air from the mainland to the ocean forms a high pressure, the mainland forms a low pressure, and the air from the ocean to the mainland forms an airflow opposite to that at high altitude, which constitutes the summer monsoon circulation. In China, there are southeast monsoon and southwest monsoon. Summer monsoon is especially warm and humid.

In winter, the mainland cools down quickly, and the temperature on the ocean is higher than that on the land, so the mainland is under high pressure and the ocean is under low pressure. The low-level airflow flows from the mainland to the ocean, and the high-level airflow flows from the ocean to the mainland, forming a winter monsoon circulation. In China, it is the northwest monsoon, which becomes the northeast monsoon. The wind in winter is very dry and cold.

But the degree of land and sea influence is related to latitude and season. In winter, the middle and high latitudes have a great influence on land and ocean. The cold high pressure center on land is at higher latitudes, while the low pressure is on the ocean. In summer, the influence of low latitude land and sea is great, the center of land thermal depression is southward, and the position of ocean subtropical high moves northward.

Of course, the seasonal movement of the planetary wind belt can also strengthen or weaken the monsoon, but it is not the basic factor. Whether the monsoon phenomenon is obvious or not is related to the size, shape and latitude of the mainland. The continental area is large, and the seasonal high and low pressure and pressure gradient caused by the thermal difference between land and sea are also large, and the monsoon is more obvious. North America is much smaller than Eurasia, with cold and high pressure in winter and low heat pressure in summer, so the monsoon is not obvious. The shape of the continent is a horizontal rectangle, and it is difficult for the warm air from western Europe to reach the eastern part of the continent, so the monsoon in the eastern part of the continent is obvious. The North American continent is a vertical rectangle, and the airflow entering the continent from the west coast can reach the east, so there is no obvious monsoon in the east of the continent. Whether from the thermal difference between land and sea or the monsoon movement of planetary wind belt, the low latitude of the mainland is conducive to the formation of monsoon. The latitude of Eurasia reaches a lower latitude, while North America is mainly distributed in the north of latitude 30, so the monsoon in Eurasia is more obvious than that in North America.

[Edit this paragraph] Monsoon-Characteristics

The regions with obvious monsoon in the world mainly include South Asia, East Asia, Central Africa, Southeast North America, East Brazil in South America and Northern Australia, among which Indian monsoon and East Asia monsoon are the most famous. There will be monsoon climate such as rainy season and dry season in areas with monsoon. In summer, the wind blowing to the mainland transports humid ocean air to the inland, where it is often forced to rise into clouds and cause rainfall, forming a rainy season; In winter, the wind blows from the mainland to the ocean, the air is dry, accompanied by sinking, and the weather is fine, forming a dry season.

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 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.