What is the humid monsoon climate in the north subtropical zone, and what changes have taken place throughout the year?

The climate in this area is characterized by warm winter and hot summer, distinct four seasons, abundant rainfall and even seasonal distribution.

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 not cold here in winter. The average temperature in 65438+ 10 is generally above 0℃, and it is hot in summer. The average temperature in July is generally around 25℃, and the direction of Xia Feng changes obviously in winter. The annual precipitation is generally above 1000 mm, mainly concentrated in summer and less in winter. This climate is most typical in the southeast of China. In other areas, because there is a considerable amount of precipitation in winter, there is little difference between winter and summer, so it is called subtropical monsoon humid climate.

This area is located between 25 and 35 north latitude and is divided according to the climate of planetary wind system. It is an arid area controlled by subtropical high. However, due to the difference between land and sea and the change of temperature and pressure field caused by the uplift of the Qinghai-Tibet Plateau, the monsoon circulation changed the circulation system of the near-surface planetary wind system, changed the arid continental climate into a humid subtropical monsoon climate, and changed the arid desert landscape into a humid evergreen broad-leaved forest landscape. After thousands of years of human activities, this area has become a densely populated and economically developed area in China.

This area is rich in heat resources, with the annual average temperature 13℃ to 20℃ and the accumulated temperature ≥10℃ from 4000℃ to 6500℃. The monthly average temperature in 65438+ 10 is above 0℃, 0℃~2℃ in the north of the Yangtze River, 2℃~ 10℃ in the south of the Yangtze River and10℃ in Nanling area. Due to the low terrain and weak barrier function, Huaiyang Mountain is often affected by cold air from the south in winter, especially Jianghan Plain and Dongting Lake Plain, which are connected to Nanyang Basin in the north and Gui Xiang Corridor in Nantong. Winter becomes a channel for cold air to move southward, where the 65438+ 10 monthly isotherm protrudes southward in a tongue shape. The absolute minimum temperature in the north of the Yangtze River can reach below-10℃, and the minimum value of-18. 1℃ has appeared in Hankou (197765438+1October 30th), and it is mostly between -7℃ and-0 in the south of the Yangtze River. Whenever strong cold air goes south, the temperature often drops above 10℃. In Shanghai, there was a record that the temperature dropped by 25.2℃ in two days. Therefore, although this area is subtropical, the winter temperature is lower than 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 of 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, Zhejiang and Anhua, Hunan have high temperatures above 465 and 438+0℃. 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 winter and hot in summer, 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 this area is generally 800 mm~ 1600 mm, which is 1~2 times more than 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 1200mm ~ 180mm, that in Nanling mountain area and hilly areas of the south of the Yangtze River is about 1500 mm, and that in the middle and lower reaches of the Yangtze River is about1200mm. 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 1800 mm.

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.

The middle and lower reaches of the Yangtze River lie in the east of the Qinghai-Tibet Plateau. In winter, the north-south jet of the westerly belt meets over this area, forming a relatively stable shear line. Coupled with the influence of Nanling Mountains, a relatively durable quasi-static front in South China appeared on the ground, with frequent cyclones and extremely rainy weather. In most areas, the average precipitation in 65438+February and 65438+1October is about 40 mm~50 mm, and it is 60 mm in February. Since March, the warm and humid air flow in the south has strengthened and the precipitation frequency has increased. In late March, Gannan first entered the spring rain period, with this as the center, the spring rain gradually extended to the northwest, southwest and northeast (figure 12. 1.2). In most areas, the spring rain doesn't end until early and middle June. There is a lot of precipitation and a long rainy period in the hilly areas of the south of the Yangtze River. In most areas, the spring rain begins in early April and ends in late May, and the rainy season lasts for 60 days. There are more spring rains in this area, and the proportion of spring rains in Changsha and Nanchang is about 40%, which is more than summer rain. In Nanjing, Shanghai, Wenzhou and other places, spring rain accounts for about 25% of the annual precipitation.