There is often a period of heavy rainfall in early summer every year in the Jianghuai River Basin of my country.

Meteorological terminology: Meiyu

A period of continuous rainy weather with heavy rainfall and frequent rainfall that often occurs every early summer (June-July) from the Jianghuai River Basin in my country to southern Japan. It is named because the plums are yellow and ripe at that time. Because the temperature is high, the humidity is heavy, and there is a lot of rain at this time, the utensils are prone to moisture and mold, hence the name mold rain. Generally, the plum blossoms start in early to mid-June and bloom in early to mid-July. After the plum blossoms bloom, midsummer begins.

Generally, in mid-to-late May, the atmospheric circulation of the pre-flood season appears in South China. As the seasons change, the atmospheric circulation will slowly change. In mid-June, when the atmospheric circulation enters the Jiangnan region, the "Meiyu" season will appear in Shanghai, Nanjing, and Hefei.

Extended information:

Formation conditions:

1. In the high latitudes of Asia, there is blocking high pressure or a stable high pressure ridge in the middle of the troposphere, and the atmospheric circulation is relatively stable. Change.

2. The westerly circulation in mid-latitudes is flat, and frequent shortwave activities provide cold air conditions for the Jianghuai region.

3. The western Pacific subtropical high has an obvious westward and northward jump process. The 500hPa subtropical high ridge is stable between 20 degrees and 25 degrees north latitude, and warm and moist air flows from the edge of the subtropical high to the Yangtze-Huaihe River Basin.

Under such circulation conditions, the Meiyu front lingers in the Yangtze-Huaihe River Basin, often accompanied by southwest vortices and shear lines, and mesoscale systems are active above the Meiyu front. It not only maintains continuous rainfall during the Meiyu period, but also provides abundant water vapor for heavy rains.