What is the origin of plum rain?

The name "Meiyu" comes from a meteorological term in China and was called Huang Meiyu in ancient times. As early as the Han Dynasty, there were many proverbs about Huang Meiyu in China. In the Jin Dynasty, there was already a record of "summer rain to the sun, named Huang Meiyu"; Since the Tang and Song Dynasties, there have been many interesting descriptions about Meiyu. Zhu He was once called "He Meizi" in the Song Dynasty. It is said that he once wrote a famous sentence in the word "Jade Case", "One Sichuan tobacco, full of wind and rain, plum rain yellow". In Song Dynasty, Chen also wrote in Geng Shi Hua: "Plum blossoms are ripe in May in the south of the Yangtze River, and it rains for ten days, which is called it". In history, "Huang Meiyu" usually refers to the precipitation of "Mei" Festival. People in the middle and lower reaches of the Yangtze River are used to taking the solar term of "Mangzhong" as May Festival, which coincides with the mature season of plums, so it is also called "Huangmei". Meteorologically, Meiyu is a unique climatic phenomenon in the process of seasonal transformation of atmospheric circulation in East Asia at the turn of spring and summer, which can be divided into typical Meiyu and early Meiyu. Typical plum rains generally "enter plum blossoms" from early June to mid-June, and bloom from early July to mid-July. Meiyu refers to the rainy days before plum blossom, which generally starts in mid-May and lasts for about half a month. After meiyu, the rain belt often recedes to the south for a period of time, and then goes north, which is a typical meiyu. In most years, the rainy season lasts for 20-25 days, ranging from more than a month to a few days. There is no plum rain in a few years, and the rain belt quickly passes through the Jianghuai Basin from South China to North China, which is called "empty plum". The rainy season in Hubei province generally begins in the middle and late June and ends on July 9 in the past 30 years. In Jiangnan, when it rains in June and July, it happens to be the season when plums turn yellow, so this rainy season is called Meiyu.