What are the criteria for plum entry and plum exit?

The starting day when the average temperature of each station is basically stable at 22℃ or above is regarded as plum blossom day. The highest temperature of each station in this area has obviously risen above 30℃, and the surface southerly wind speed has also obviously increased, so it is designated as Meihua.

According to the principle of combining circulation conditions with regional precipitation, during the period from late May to the first half of July, the ground peak activity is frequent within the range of 29-33 north latitude, with six rainy days for two consecutive weeks. At the same time, referring to the lower reaches of the Yangtze River, the average temperature of each station is basically stable above 22℃, which is the start date of entering Mei. In the time curve of rainy days, rainfall, cloud cover and other climatic factors in early summer, there are also days that suddenly increase (that is, there is a turning point), which is regarded as the average plum blossom period.

During the Meiyu period, the Meiyu front system and the main rain belt obviously moved out of the middle and lower reaches of the Yangtze River. If there are less than two rainy days in the five days in this area, the maximum temperature of each station in this area will obviously rise above 30℃, and the southerly wind speed on the ground will also obviously increase, so it will be designated as plum blossom. China's current almanac uses the statement of Shenshu Jing, saying that after the slight summer heat, plum blossoms will bloom between July 8 and 19.

Seasonal distribution of plum rains

Meiyu mainly occurs in the middle and lower reaches of the Yangtze River in China, Taiwan Province Province in China, Liaodong Peninsula, the southernmost tip of the Korean Peninsula and the subtropical monsoon climate zone in south-central Japan. There is no plum rain in other parts of the world at the same latitude. There is no obvious plum rain in South China.

Although Meiyu is a unique weather and climate in the middle and lower reaches of the Yangtze River, its appearance is not isolated, but closely related to the north-south displacement of a large-scale rain belt.

In the east of China, east of 1 10E, the main rain belt swings in Nanling Mountains and its south area from mid-April to early May in flood season. In recent years, although it moved to the north of Nanling within a certain period of time, it often stayed in the south of 28N and 29° n from a waiting period (5 days) or the multi-year average of 10 days. This period is called "rainy season in the south of the Yangtze River" or "pre-flood season in South China".

Reference to the above content: Baidu Encyclopedia-Chumei

Baidu Encyclopedia-Entering Plum