I. Geographical factors
1. The influence of latitude and longitude on China's climate: the mid-latitude is the main body, and the latitude across the north and south is large, with the mid-latitude climate as the main body.
2. Impact of land-sea pattern on climate in China: East Asian monsoon is the most typical monsoon climate in the world, which is formed in the eastern part of Eurasia and the west coast of the Pacific Ocean.
3. Topographic factors: China's mountainous areas are numerous and high, with complex trends, which have multiple functions such as lifting, blocking and diverting air masses, leading to complex climate differentiation.
4. Underlying surface factors: The underlying surface environment in China geographical space is complex and diverse, and there are many large-scale geomorphic units with relatively uniform properties, forming many typical local climates.
5. Ocean current factor: The Kuroshio warm current is the main part of China offshore, which can increase the temperature and humidity of the transit air mass and strengthen the summer monsoon.
6. Impact of the Qinghai-Tibet Plateau: The Qinghai-Tibet Plateau is the highest plateau in the world, with high terrain and an average elevation of 4,000-5,000 meters. There are many peaks standing above the snow line, with a height of over 6000-8000 meters. The outer edge of the plateau, surrounded by high mountains, stands on the basins and plains with a height difference of 3000 ~ 7000 meters around, setting off the majestic momentum of the plateau. The plateau covers an area of 2.5 million square kilometers, with a length of 3,000 kilometers from east to west, a width of 1.5 kilometers from north to south and a latitude of 1.5. Moreover, the plateau accounts for almost more than 1/3 of the mid-latitude troposphere thickness in winter, which has become a huge obstacle to the mid-latitude atmospheric circulation. It has undoubtedly played a great role in the formation of climate in China.
(1) block the exchange of cold air on both sides of the plateau, and expand the influence range of westerlies.
The huge Qinghai-Tibet Plateau, like the impact of a big stone in the center of a river that is not exposed to the water, makes the westerly belt below 500 millibars (3-4 kilometers) branch and flow around in winter, forming two air currents in the north and south. Part of the north branch air flow blows into Tarim Basin along Altun Mountain, and the other part blows into Hexi Corridor along Qilian Mountain. The two air flows merge into the northwest air flow in the eastern part of the plateau, and the streamline bends in an anticyclonic way, forming a dynamic high pressure ridge, which further strengthens the cold high pressure on the surface of the plateau and is beneficial to the south of the winter monsoon. The bondage of the plateau makes the winter wind stronger. The south branch airflow is the northwest airflow in the southwest of the plateau, bypassing the south side of the plateau and turning into the southwest airflow. The streamline bends in a cyclone, forming a dynamic trough of low pressure. Under the influence of warm and humid air flow in front of the trough, the winter climate in south China is quite different from that in north China. The north-south airflow meets in the middle and lower reaches of the Yangtze River, forming the strongest westerly belt in the northern hemisphere. The existence of the Qinghai-Tibet Plateau has caused cold air to pour into the southern latitudes of eastern China because of the blocking and squeezing of the plateau topography. The southwest area on the east side of the plateau is located in the leeward position of the westerly belt of the plateau, with low wind speed and unique weather and climate.
The dynamic function of the Qinghai-Tibet Plateau is also manifested in its blocking effect on the near-surface airflow. In the east-west direction, it prevents the weather system from moving eastward with the westerly airflow, and in the north-south direction, it directly blocks the north-south exchange of cold and warm air in the troposphere in western China. The winter plateau blocks the winter wind from going south, which makes India in the south have higher temperature, lower air pressure and lower annual temperature compared with other regions in the same latitude. At the same time, the pressure system in the westerly belt is blocked, weakened and disappeared by the plateau in the west, while the Sichuan basin in the east is relatively calm, with less airflow disturbance and weak wind force. The northern side of the plateau is not easily affected by the warm and humid air flow in the south. It is conducive to the accumulation of cold air, further strengthening the strength of Mongolian high pressure, and then having a strong cold current impact on the eastern region of China. However, the plateau prevented the humid air from entering the northwest basin of China, resulting in dry, hot and rainy weather, which made Xinjiang extremely dry and became a rare area with little rain and no flow.
(2) The appearance of plateau monsoon makes the monsoon climate in China particularly prominent.
The physical properties of the surface of the Qinghai-Tibet Plateau are completely different from the highly free atmosphere. In summer, the plateau becomes a heat source, and the airflow converges on the surface of the plateau, forming the Qinghai-Tibet thermal depression. This thermal depression gradually evolved from spring, basically formed in early May and June, and reached its strongest in midsummer. Its formation destroyed the continuous distribution of subtropical high in the northern hemisphere. In winter, the surface of the plateau cools rapidly, and the terrain is high and the ice and snow area is large, forming a low temperature and high pressure center. The formation of plateau thermal depression in summer is beneficial to the convergence of air flow over the plateau, while it is beneficial to the divergence of air flow over the plateau in winter. The seasonal variation of pressure field causes the seasonal variation of local circulation. The air around the plateau flows to the plateau in summer, and the air around the plateau flows to the plateau in winter, thus forming the plateau monsoon.
The cold high pressure in winter strengthens the sinking of air flow in the neighboring areas. The superposition of the cold high on the plateau and the Mongolian high strengthens the Mongolian high on the north side of the plateau, and its power is particularly strong. Winter winds affect most parts of China. In summer, the plateau thermal depression attracts the atmosphere to converge to the plateau, which further strengthens the Indian depression on the south side of the plateau. It has a stronger pressure gradient with the Pacific subtropical high and the southern hemisphere subtropical high, which strengthens and accelerates the southwest and southeast monsoon. The air flow field formed by the configuration of the plateau pressure field in winter and summer coincides with the Eurasian pressure field in winter and summer and its air flow field, thus strengthening the intensity of the winter and summer monsoon in China. It also changed the pressure field in China and increased the typicality, extensiveness and complexity of the monsoon climate in China.
(3) Unique plateau climate
The Qinghai-Tibet Plateau plays an extremely important role in the atmospheric circulation in the whole mid-latitude region, and at the same time, it has formed a unique plateau climate in its region, which has a great influence on the climate formation in China and even Asia.
(4) The influence of Qinghai-Tibet Plateau on the temperature distribution in China.
Influenced by latitude, land and sea distribution and terrain fluctuation, the overall characteristics of temperature distribution in China are warm in the south and cold in the north, with a large temperature difference, while the influence of Qinghai-Tibet Plateau has greatly changed the temperature distribution in China.
A. In summer, the phenomenon of cold in the south and cold in the north appears in the western region, which is contrary to the latitude variation law of cold in the south and cold in the north. In summer, the temperature is very high all over the country. Although the isotherm is parallel to the coastline, it still has the changing law of hot in the south and cold in the north. However, the average summer temperature in the Qinghai-Tibet Plateau in the west is higher than that in the Tarim Basin in the north. At the same time, the mountainous area on the northern edge of the plateau has a blocking effect on the heat emission of the Tarim Basin, which is the hottest place in summer in China. However, the plateau has become the cold pole of the whole country in summer.
Yunnan-Guizhou Plateau in the east of B Plateau is in the leeward position of westerly belt in winter, and there is a "dead water area". In the south, winter is not cold, the temperature is high and the weather is unique. Kunming is known as the "Spring City", which is very important.
C. The temperature in plateau area is influenced by topography, which shows that the isotherm is obviously consistent with the contour line, breaking the law of temperature change in winter and summer in China.
D. Due to the high terrain and cold weather in the plateau area, the winter is long and there is no summer, and the average temperature in July is still below 8℃. The accumulated annual activity temperature is less than 2000℃, and the duration of ≥ 10℃ is less than 100 days. In some areas, the annual average daily temperature is below 0℃, and the active accumulated temperature is zero. It can be divided into three temperature zones: plateau cold zone, plateau sub-cold zone and plateau temperate zone.
(5) The influence of Qinghai-Tibet Plateau on precipitation in China.
The precipitation in China mainly comes from the southwest monsoon and southeast monsoon of summer circulation, which is relatively abundant and has the law of gradually decreasing from southeast to northwest in regional distribution.
A. The topographic precipitation is obvious in the mountainous areas on the edge of the plateau, with the precipitation on the south slope reaching more than 2,000 mm, 200-400 mm in the eastern region and 400-800 mm in the southeast edge region. ..
B. The plateau blocked the southwest monsoon and southeast monsoon, and could not enter the northwest inland area of China, so the Tarim Basin became an extremely arid area in China. The precipitation in most areas is below 100 mm, and in some areas it is below 50 mm.
C the establishment of the Qinghai-Tibet cold high and the speed of its disappearance also directly affect the intensity of the monsoon. The cold high pressure is established early and its intensity is high, and the winter wind is controlled quickly and widely in China. The disappearance of the later period and the outward divergent airflow prevented the summer monsoon from going northward, which directly restricted the precipitation in the eastern part of China. Therefore, the changes of cold high pressure and hot low pressure on the Qinghai-Tibet Plateau also affect the precipitation intensity and even the drought and flood disasters in China to a certain extent.
Second, the radiation factor.
The annual total radiation distribution in China is about 90 ~180× 4.1868kj/cm2. See figure 8. 192 of the textbook. The maximum value is on the Qinghai-Tibet Plateau, and the minimum value is in the Sichuan Basin in the middle and lower reaches of the Yangtze River, with the range of10 ~120× 4.1868kJ/cm2.
The total effective radiation on the ground in China is about 35 ~ 55× 4. 1.868 kJ/cm2, and there is more effective radiation in areas with more total radiation throughout the year. In areas with less radiation, there is less effective radiation. Therefore, the maximum value is in the Qinghai-Tibet Plateau, the minimum value is in the Sichuan Basin, and the middle and lower reaches of the Yangtze River are between 35 ~ 45× 4. 1.868 kJ/cm2.
The annual radiation difference in China is about 45 ~ 80× 4. 1.868kJ/cm2, the maximum value is in the Qinghai-Tibet Plateau, the minimum value is in the Sichuan Basin, and the middle and lower reaches of the Yangtze River are between 50 ~ 60× 4. 1.868kJ/cm2. Seasonal radiation difference: Generally, the total radiation in each season is the most in summer and the least in winter, followed by summer, spring, autumn and winter. However, there are exceptions. For example, in Tengchong, Yunnan, due to the rainy summer, the radiation amount in summer is less than that in spring and autumn, which is equivalent to that in winter, and the radiation amount is spring, autumn, summer and winter in turn. Seasonal radiation difference and its temperature state, the radiation difference in most areas is the largest in summer, the smallest in winter, and between spring and autumn. The same is true of the temperature in each season, with the highest in summer and the lowest in winter, with spring and autumn in the middle.
Third, the circulation factor.
The circulation mode of the lower atmosphere in China is mainly monsoon circulation, and the weather system that dominates monsoon circulation has different performances in each season of the year.
In winter, three activity centers dominate the atmospheric operation in China: Mongolian high, Aleutian low and equatorial low. The air pressure is low in the east and high in the west. Therefore, the winter winds in China blow from the mainland to the sea, with westerly winds in the northeast and northerly winds in North China. Because there is also a low pressure in the South China Sea (equatorial low pressure), there is also a pressure gradient in the north and south of China, and some cold air will go south along the coastline, affecting the southern provinces of China. The winter wind in these areas is northerly. When the Aleutian low pressure is strong, a lot of cold air moves eastward, but there is less cold air moving southward, and most parts of China have warm winters; On the contrary, when the Aleutian low pressure is weak, there is less cold air flowing eastward and more cold air flowing southward, and most parts of China are cold in winter.
In summer, the North Pacific subtropical high in the southeast sea and the Indian low in southwest China form a pressure situation of high in the east and low in the west, so the summer monsoon in most parts of China is southeast wind; In addition, there is a warm and humid air current blowing from the Bay of Bengal in the southwest of China in summer, so sometimes the southwest wind or southerly wind blows.
At the same time, the climate of China is also deeply influenced by the westerlies in the northern hemisphere.
References:
Zhang Hang. Influence of Qinghai-Tibet Plateau on Climate in China. Journal of College of Adult Education of Shaanxi Normal University, No.4, 1999.