When is the reason for the rainy season?

Plum rains are continuous, usually in the south. When the rainy season comes every year, it will rain continuously for a long time. So when did the plum rains form? How long will it last? What regions and cities do they cover?

Intermittent rain in Mao Mao (middle and lower reaches of the Yangtze River)

A unique phenomenon in a year. After mid-June, the rain belt remained in the Jianghuai basin, that is, Meiyu. (However, due to the current language usage habits, Meiyu is not limited to the Jianghuai Valley to Japan, and the continuous precipitation in East China such as Fujian during the Meiyu season is also called Meiyu. )

The stay time of rain belt is called "Meiyu season", the start day of Meiyu season is called "entering plum" and the end day is called "leaving plum".

In addition, due to the high air humidity during this period, everything is easy to be damp and moldy, so people gave Meiyu an individual name, called "moldy rain". Five Miscellaneous Torches by Xie Zaihang in Ming Dynasty. "Tianbu No.1" records: "Every year in March and April in the south of the Yangtze River, there is constant bitter rain, and everything is moldy and rotten. As the saying goes, it is called plum rain, and the plums are green and yellow. Be proud of

: the reasons for the formation of plum rain

1. The middle and lower reaches of the Yangtze River are located in the mid-latitude area in the eastern part of Eurasia. On the one hand, they are influenced by the cold air from the cold zone to the south, and on the other hand, they are influenced by the warm and humid airflow from the tropical ocean to the north. Every spring, the warm and humid air flow gradually strengthens, entering the mainland from the sea, from south to north, and often extending to the middle and lower reaches of the Yangtze River in early summer. Especially at the low altitude of two or three kilometers, there is often a very humid strong southerly airflow blowing from the ocean, and the wind speed reaches about ten to twenty meters per second. When it entered Chinese mainland, it encountered cold air from north to south. Cold and warm air meet, forming a front at the junction, and precipitation appears near the front. Meiyu belongs to frontal precipitation.

2. If the cold air is strong, the cloud and rain area will move southward with the cold air; If the warm air is strong, the cloud and rain area will move northward with the warm air. Therefore, they will not stay in one area. In the middle and lower reaches of the Yangtze River in early summer, on the one hand, the warm and humid airflow is quite active, on the other hand, the cold air from north to south still has a certain intensity, especially in the air layer near the ground, and a small amount of cold air often goes south. In this way, cold and warm air confronts each other in this area, forming a stable rainfall zone. This rain belt is only 200-300 kilometers from north to south, but it can reach about 2000 kilometers from east to west. It spans the middle and lower reaches of the Yangtze River and reaches Japan in the east.

Which cities will have plum rains?

Wuhan, Nanchang, Shanghai, Hangzhou and Nanjing are all typical cities of Meiyu. The rainfall in late June is incomparable to other periods of the year. Among them, in the eastern part of Shanghai and Nanjing, the number of precipitation days in late June is the most in the whole year. Compared with Wuhan, Nanchang and Hangzhou in the southwest, the rainy days are the most in late March (the spring rain is more lingering).

The cities with the most precipitation in late June are Suzhou and Changzhou in Jiangsu, Wuhu, Anqing and Huangshan in Anhui, Jingdezhen and Lushan in Jiangxi, Huangshi in Hubei, Changde and Sangzhi in Hunan.

When does the plum rain start?

Every year from late May to early June, the cold air in the north meets the warm air from south to north in South China, forming a quasi-static front in South China. Around the end of June, the warm air force strengthened, and the quasi-static front moved northward to the Jianghuai area, becoming the quasi-static front of the Jianghuai area (also known as Meiyu front).

How long?

For several days in a row, the sky was gloomy and the precipitation was constant, sometimes big and sometimes small. Therefore, there is a popular saying in southern China: "When the rain hits Huangmei's head, there will be no sun for forty-five days". Continuous rain, high temperature and high humidity are the main characteristics of plum rain.