What is plum rain? What is the cause of Meiyu?

Meiyu is in the middle and lower reaches of the Yangtze River in China, Taiwan Province Province, south-central Japan and south Korea. Every year in June and July, there will be continuous rainy weather. Because it is the mature period of plums in Jiangnan, it is called "Meiyu", and this period is called Meiyu season.

Reasons for the formation of plum rain:

1. There is blocking high pressure or stable high pressure ridge in the middle troposphere in high latitudes of Asia, and the atmospheric circulation is relatively stable with little change.

2. The westerly circulation in the mid-latitude area is gentle, and frequent short-wave activities provide cold air conditions for the Jianghuai area.

3. The western Pacific subtropical high has an obvious process of extending westward and jumping northward. The ridge line of the 500 HPA subtropical high is stable between 20 and 25 degrees north latitude, and the warm and humid air flow is transported from the edge of the subtropical high to the Jianghuai basin. Under this circulation condition, Meiyu front lingers in the Jianghuai basin, often accompanied by southwest vortex and shear line, and the mesoscale system on Meiyu front is active. It not only maintains the continuous precipitation during the Meiyu period, but also provides abundant water for the rainstorm.

Extended data

There are many proverbs that use winter weather characteristics to predict plum rains. For example, "there is more snow in the twelfth lunar month, and the water is yellow and the plum blossoms are fragrant", which means that the snow in the twelfth lunar month is positively related to the plum rains.

"Cold water is dry, so is summer water", and "dry" means less rain. When there is less rain in winter, there is less plum rain. This is because the weather often has stages. Persistent drought is often caused by the relative stability of a weather situation conducive to drought. However, due to the constant movement of the atmosphere, the above-mentioned relatively stable state will always be destroyed and will turn to the opposite side under certain conditions.

"Spring water overflows and summer water dries up", and "flooding" means that there is more rain than normal. As the saying goes, if there is more rain in spring, there will be less plum rain in summer, which is easy to dry. Like "peach blossoms must be dried plum blossoms", spring rains are used to predict plum rains.

"Where there is spring breeze, there must be summer rain". Spring breeze refers to the east wind (mostly southeast wind), and summer rain refers to plum rain. The proverb means that when there is a lot of easterly wind in spring, there is usually a lot of plum rain in summer.

Baidu Encyclopedia-Meiyu