Distribution law of subtropical monsoon climate

The subtropical monsoon climate is distributed on the east coast of subtropical continent at 25 ~ 35 north latitude, and it is a zone where tropical marine air masses and polar continental air masses alternately control and compete with each other. It is mainly distributed in the south of Huaihe River in Qinling Mountains in eastern China, north of tropical monsoon climate, south of Japan and south of Korean Peninsula. It's warm in winter here, and the average temperature in Leng Yue is above 0℃. Summer is hot, the average temperature in the hottest month is above 22℃, and the temperature changes obviously in seasons with four distinct seasons. The annual precipitation is generally 800 ~ 1 500mm, which is more in summer, but there is no obvious dry season. Compared with the temperate monsoon climate, the seasonal changes are basically similar, except that the winter temperature is higher and the annual precipitation increases.

Although it is subtropical, the temperature in winter is lower than that in other parts of the world at the same latitude. Due to the low temperature in winter, the subtropical latitude of China is south, and its northern boundary is 4~5 latitudes south than the theoretical boundary. Compared with the Mediterranean region, it is 10~ 1 1 latitude to the south. However, subtropical areas in China, especially central China, are generally hot in summer, with the average temperature in July around 28℃ and some areas exceeding 29℃. High temperature weather above 35℃ often occurs from May to September. July-August is controlled by subtropical high, with many sunny days and long sunshine hours. The frequency of high temperature is the highest, and the absolute high temperature often exceeds 40℃. Jinhua, Lishui, Zhejiang and Anhua, Hunan all have high temperature meteorological records above 4 1℃. The average temperature in April and1October is 16℃~2 1℃, and the temperature in autumn is slightly higher than that in spring.

Generally speaking, the middle and lower reaches of the Yangtze River are warm in spring and cool in autumn, hot in summer and cold in winter, with four distinct seasons. Generally, winter is 1~4 months long, about 4 months north of the Yangtze River, and less than 1 month in Nanling area; Summer lasts for more than four months, generally ending from mid-late May to late September, and arriving at the beginning of 10 at the latest in the south. The length of spring and autumn in most areas is 2 months each, and it can reach 3 months in the south.

The average annual precipitation in subtropical monsoon climate zone is generally 800 mm~ 1500 mm, which is twice as much as that in North China and richer than that in Southwest China. The distribution of precipitation decreases from southeast to northwest. The annual precipitation in hilly areas of Zhejiang Province is 1200 mm~2000 mm, that in Nanling mountain area and hilly areas of the south of the Yangtze River is about 1500 mm, and that in plain areas of the middle and lower reaches of the Yangtze River is1000 mm ~1200 mm.. The influence of topography on precipitation is also remarkable. Generally, there are more mountains than flat land, and there are more windward slopes than leeward slopes. For example, Tunxi in Anhui is very close to Huangshan, and the precipitation in Huangshan is 700 mm more than that in Tunxi (Tunxi 1507.8 mm, Huangshan is 2263.9 mm). The annual precipitation of Luoxiao Mountain and Xuefeng Mountain can exceed 180 cm.

In the seasonal distribution of precipitation, summer rain is the most, followed by spring rain, autumn rain is worse, and winter rain is the least, but winter rainfall can also account for more than 10% of the annual precipitation. The middle and lower reaches of the Yangtze River are areas with high proportion of winter rain and abundant spring rain in China.

This seasonal distribution of precipitation is closely related to the geographical location of the middle and lower reaches of the Yangtze River and the atmospheric circulation process.