Meiyu, mildew and weather related knowledge

This is a season that only exists in humid areas in the south. There are two versions: one is called Huang Meiji, which means when plums turn yellow and mature. Because it happens to be the time when the air humidity is the highest in the south, things are easy to get moldy, so it is also called "yellow mold day"

Mild weather

From May to June all the year round, our province enters a long period of rainy weather from north to south, sometimes at intervals, sometimes with continuous heavy rain or rainstorm, which is the rainy season in our province. Because of the continuous rain, the temperature is relatively high, the air is humid, and clothes are prone to mildew. This kind of weather is commonly known as "mildew rain".

According to the statistics of meteorological data for many years, the mildew rain started from north to south in mid-May and ended from south to north in mid-June. The average is about 40-50 days, and the rainfall increases from southeast to northwest, about 360-660 mm, accounting for more than one third of the total annual rainfall. However, the specific start and end period of the annual mildew rain may be advanced or postponed. For example, 1973 and 1980 entered the mildew rainy season on April 19, while 1963 did not enter the mildew rainy season until May 30; Another example is the mildew rain in southern China. 1980 and 19 1 ended on June 4-5, while 1976 did not end until July 12. In a special year like this, the difference between morning and evening can be more than one month.

During the mildew rain, heavy rain, heavy rain and even heavy rain are common disastrous weather. If the rainfall is too concentrated or too large, it will often lead to the surge of river water level, which will lead to floods. According to records, since 1935, the hydrological data of Zhuqi water level in the lower reaches of Minjiang River show that the highest water level appears in May-June every year, accounting for more than 80%. Therefore, the rainy season is the main period of flood control and fighting in our province.

The formation of mildew and rain weather is mainly the result of the intersection of cold and warm air. After entering May, although the intensity of cold air has weakened, it often affects the basin south of the Yangtze River. At this time, the summer monsoon over South China has been quite active. In this circulation situation, the warm and humid air in the south is constantly transported to the north, and the cold and warm forces confront each other, thus causing heavy rain or heavy rain and forming a specific rainy weather.

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

In early summer, there are often long rainy days in the Jianghuai basin. At this time, the utensils are easy to be moldy, so it is also called "moldy rain" or "mildew" for short; It is also called "Plum Rain" or "Huang Meiyu" because plums in the south of the Yangtze River are yellow and ripe. It is recorded in China's historical records. For example, The Book of Beginners quoted the compilation of Emperor Liang Yuan in the Southern Dynasties, "Plum blossoms have plum rains when they are ripe". Liu Zongyuan's Plum Rain in the Tang Dynasty: "Shi Mei welcomes the rain, and it is worth the late spring." Wait a minute. It is recorded in China's almanac that there is mildew rain all day: it is called "mildew" at the beginning and "mildew" all day long. The first day after the awn is planted, it will be moldy, but it will not be moldy on the first day after the light summer. Mold always enters between June 6~ 15 and leaves between July 8~ 19. There is an obvious rainy season in the eastern part of China, with a long rainy period and relatively concentrated rainfall, which is caused by the displacement of the main rain belt from east to west to north, and is a unique phenomenon in the turn of atmospheric circulation in East Asia at the turn of spring and summer. After mid-June, the rain belt remained in the Jianghuai basin, which is Meiyu. The time that the rain belt stays is called "Meiyu season", the day when the rainy season begins is called "entering the plum blossom", and the day when it ends is called "emerging the plum blossom".

In addition, due to the high humidity in the air during this period, everything is easy to be damp and moldy, so people gave Meiyu an individual name, called "Moldy Rain". Xie Zaihang's Five Miscellaneous Torches in Ming Dynasty? "Tianbu No.1" describes: "Every year in March and April in the south of the Yangtze River, it rains bitterly, and everything is moldy, commonly known as Meiyu, and it is covered when it is green and yellow. From Xu Huai to the north, it is often dry in spring and summer. At the turn of June and July, it rained heavily and everything was moldy. " Li Shizhen, an outstanding medical scientist in Ming Dynasty, pointed out more clearly in Compendium of Materia Medica: "Plum rain or mildew rain, when it comes to clothes and things, will produce black mold." .

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