The meaning of entering plum blossom and leaving plum blossom

Lead: Plum rainy days are common weather in the middle and lower reaches of the Yangtze River, which can be divided into plum blossoms and plum blossoms. Let's have a look!

Plum entry and plum exit, also known as mold entry and mold exit. Every year, the rainy weather in the plum yellow ripening season, referred to as "Huang Meiyu" or "Meiyu", makes clothes easy to get moldy.

Plum entering and plum leaving refer to the beginning and end of rainy season respectively. Maggie is calculated according to the date of the main branch:

The first and third day of planting plum in the awn;

The first day of plum blossom in hot summer.

For example, in 2005, the date of planting awn was June 5, and the first day of planting awn was June 1 1, which was the day of plum blossom; Until the first Sunday after the summer heat (July 7th), that is, July 6th 10.

How to determine the date of plum entry and plum exit?

The traditional entry and exit of plums is related to heavenly stems and earthly branches. The meteorological significance of entering Mei has specific indicators.

Traditionally, in China, the judgment of plum entry and plum exit is based on the combination of solar terms and branches. According to the calendar, the first third day after mango seeds is plum blossom, and the first last day in Xia Hou is plum blossom. If the weather on the awning day is C, it is designated as entering the plum blossom, and if it is not in the shallow summer, it is designated as leaving the plum blossom.

Meteorological significance of plum blossom

Definition of Meiyu: From the middle and late June to the early summer of the first half of July, there is often a continuous rainy period from the middle and lower reaches of the Yangtze River (or Jianghuai Basin) to southern Japan, with frequent precipitation processes and frequent heavy rains. At this time, it is the mature period of plums in Jiangnan, so it is called "Meiyu". The ancient poem "It rains at home in Huangmei season, and frogs are everywhere in the grass pond" vividly depicts the natural scene of the local rainy season. Because of the high humidity and temperature in the rainy season, clothes are easy to get moldy, so it is also called "mildew rain". Except China, there are plum rains in the southernmost part of South Korea and south-central Japan, but not in other parts of the world at the same latitude. Therefore, Meiyu is a unique weather and climate phenomenon in East Asia.

Meiyu area in China starts from Huaihe River in the north and ends in the middle of Fujian, Jiangxi and Hunan provinces in the south, roughly between 27 and 34 east of east longitude110, and the length of Meiyu period is the longest in the middle of Meiyu area. On average, Shanghai entered Mei on June 15, and blossomed on July 9, with a length of 25 days. Generally, there are only about 20 days near the north-south boundary line in Meiyu area. But this is the average climate, which may change greatly every year. For example, in the morning and evening, the plum blossom period can be 40 days apart, and the plum blossom period can be 45 days apart; The longest meiyu period can be as long as 60 days or even longer, and some years are even longer, while some years have basically no meiyu, which is called "empty plum". The year with the highest rainfall in Meiyu period is 1954, and the total rainfall in Meiyu period in that year is more than twice the average for many years. The division of meiyu and meiyu period is mainly based on the seasonal turning and adjustment of atmospheric circulation. In the analysis of circulation adjustment, the steady northward movement of warm and humid air flow, that is, the northward movement of the ridge line of the western Pacific subtropical high at 120 degrees east longitude, is the main position, supplemented by the circulation adjustment of the westerlies. According to the above principles, the adjustment date of plum blossom circulation is determined first, and then the plum blossom period is divided according to the start and end dates of large-scale precipitation.

First, the criteria for Shanghai Meiyu index to enter Mei: the ridge line of the subtropical high is north of 18 N five days before entering Mei; In addition, the average temperature between China and Japan must be ≥22℃ for at least 3 days within 5 days, and there must be ≥ 4 rainy days (including meteorological stations in all districts and counties) within 5 days after entering Mei. If the plum rains are segmented, the temperature after each segment of plum rains shall be ≥22℃. Pruning standard: Before and after the end of the Meiyu, the ridge line of subtropical high jumped northward to 26 N or north between 120- 130 E, with the daily average temperature ≥27℃ and the highest temperature ≥30℃, and there was no rain for more than 6 days. If it rains again, it will be summer rain, not plum rain.

2. Daily adjustment index of Meiyu index in Jiangsu Province: From May to June, when the stable westerly wind at 500hPa in Kolkata ends and the east and west winds alternate, it reaches the following index for three consecutive days: (1) 120 E subtropical high ridge ≥ 20n. (2) The average position of line 588 is at east longitude11. Daily index of circulation adjustment during plum blossom: it appears three days after plum blossom: (1)120 e subtropical high ridge ≥ 27 n (or longitude115 e,120 e,/kloc. (2) At120 E, the position of -8℃ isotherm is ≥ 40 N. ..

Three. Meiyu index in Zhejiang: (1) Plum-entering index appears for more than 5 consecutive days (daily rainfall ≥0. 1mm, two days of daily rainfall ≤ 1.0mm or one day without rain is allowed). After that, there will be rainy weather, and there will be no rainy weather for more than 5 consecutive days. Meiyu is defined as daily rainfall ≥1mm. Reference index: At the same time, the subtropical ridge jumped northward to 20 north latitude, and the stability time exceeded 10 day, and remained stable for three consecutive hours. (2) The continuous rainy weather with plum blossom index of more than 5 days (daily rainfall ≥0. 1mm) ends, and there is no rainy weather for more than 5 days (rain 1 day is allowed), and the date of the last daily rainfall ≥0. 1mm is the plum blossom date. Reference index: The ridge line of subtropical high jumped northward to 25 N and remained stable for two hours. During this period, rainy weather with daily rainfall not exceeding 1mm occurred for five consecutive days, and the date of the last daily rainfall ≥ 1mm was taken as the date of plum blossom.

4. Meiyu index in Anhui: (1) subtropical high at the ridge line of (1) east longitude 120 for at least 4 consecutive days, and the position of subtropical high ridge line is not considered when there is a typhoon. (2) The average daily temperature is ≥22℃ for more than 4 consecutive days (Hefei is the representative between Jianghuai and Anqing along the river). After plum blossom, the temperature is allowed to be lower than this value. (3) The difference between the daily average temperature and the daily average absolute humidity is negative for more than 4 consecutive days, and it is allowed to be positive when the rainy season is interrupted (Hefei Station in the north and at least two stations in Anqing, Wuhu and Tunxi in the south meet this requirement). (4) The starting date of continuous rainy days after meeting the above three criteria is regarded as the date of plum blossom (if the starting date of continuous rainy days is earlier than the date of meeting the above three criteria, the starting date of continuous rainy days in advance is regarded as the date of plum blossom). (2) The ridge line of subtropical high in Meizhou for more than 4 consecutive days (1) east longitude 120 ≥ 27 north latitude (only 26 north latitude is needed in the south of a few years). (2) Line 588 began to stably control the area south of Huaihe River for ≥4 days. (3) The average daily temperature has remained above 28℃ for more than 4 consecutive days. The end date of continuous rainy or obvious precipitation near the start date of one of the above three items is designated as the end date of Meiyu, and the next day is designated as Plum Blossom Day. (3) Meiyu period: from the date of plum blossom to the day before the date of plum blossom is Meiyu period. If the rainy season is segmented, the rainy season is segmented. (4) The earliest plum blossom date in the northern and southern parts of the province is the plum blossom date in the province, the later plum blossom date in the two areas is the plum blossom date in the province, and the day before plum blossom to the plum blossom date is the plum rain period in the province.

Verb (abbreviation of verb) Division standard of rainfall concentration period in Jiangxi Province: Division standard of single-station rainfall concentration period. The obvious floods in Jiangxi Province mainly occur from April to July. The duration of heavy precipitation can reach 1 ~ 10 days, and the daily rainfall is also between 25 mm and 400 mm. This continuous period of heavy precipitation is called rainfall concentration period. The calculation formula of rainfall concentration period at a single station is as follows: δ = [∑R-a (n-1)]/100, where ∑ r is the sum of rainfall in n days and n is the number of days of heavy precipitation. According to the precipitation situation in Jiangxi province over the years, n is determined to be 1 ~ 10 days, and the coefficient a is 25. The coefficient α can take different values in different regions. See the following table for the days of concentration period and the lower limit of rainfall in this period calculated by the formula: days of concentration period 1 2 3 4 5 6 7 8 9 10 lower limit rainfall (mm)100125150175 200 225 250 270. In the middle and lower reaches of the Yangtze River, besides the short-term floods caused by tropical cyclones, the general trend of drought and flood is mainly determined by the abundance of plum rains.