How is the rainy season formed? How is the rainy season formed?

The Meiyu is produced in the frontal region of the edge of the western Pacific subtropical high (known as the Meiyu front), which is the product of the interaction between the polar air mass and the subtropical air mass. The location and stability of the Meiyu rain belt are closely related to the location and intensity of the subtropical high (the ridge line is generally stable between 20° and 25°N), and also related to the circulation situation of the westerly wind belt that is not conducive to the southward movement of cold air to the Yangtze River Basin. At the beginning of June every year, when the situation of atmospheric circulation is relatively large, the ridge of the subtropical high in the western Pacific jumps to the north of 20°N, and it begins to be human.

When the ridge line of the western Pacific subtropical high jumps further northward and crosses 25°N, the Meiyu period ends, and the Yangtze River basin enters a period of drought.

In early summer, there is often a long period of gloomy and rainy weather in the Yangtze-Huaihe River Basin. At this time, the utensils are easy to mold, so it is also called "mold rain", referred to as "mold"; It is also the time when the plums in the south of the Yangtze River are ripe, so it is also called "plum rain" or "yellow plum rain". There are many records in Chinese historical books.

For example, "Beginner's Notes" quotes the "Compendium" of Emperor Liang Yuan of the Southern Dynasty: "The plum is ripe and the rain is called the plum rain". Tang Liu Zongyuan's "Plum Rain": "Mei Shi welcomes the rain, and the vast is in late spring."

Wait. In the Chinese almanac, there are records of the beginning and end of the mold rain: the beginning day is called "mold", and the end day is called "mold".

After the miscanthus planting, the first day of mold, after the summer heat, the first day of mold. The arrival of mildew is always between June 6 and 15, and the mold is always between July 8 and 19, and there is an obvious rainy season in eastern China with a long rainy period and relatively concentrated rainfall, which is caused by the north-south displacement of the main rainfall belt in the east-west direction, which is a unique phenomenon of the East Asian atmospheric circulation during the transition of the spring and summer seasons. After mid-June, the rain belt remains in the Jianghuai River Basin, which is the plum rain.

The duration of the rainy season is called the "rainy season", the day that begins the rainy season is called "Izume", and the day that ends is called "Izume". In addition, because the air humidity during this period is very high, all things are very easy to get damp and mildew, so people give the rainy season another name, called "mildew rain". Ming metabolism in Hangzhou's "Five Miscellaneous Torches 6 1 Days Part 1" describes:

Jiangnan every year. In March and April, the bitter rain does not stop, all things are mildew, commonly known as the plum rain, and when the plum is green and yellow. From Xuhuai to the north, there is often drought in spring and summer, and at the turn of June and July, the rain does not stop, and the things are moldy." Li Shizhen, an outstanding medical scientist in the Ming Dynasty, pointed out more clearly in the "Compendium of Materia Medica":

The rainy season may be mildew, and it is said that it is stained with clothes and things, and black mold is also produced."

In the high latitudes of Asia, there is a blocking high or stable ridge of high pressure in the middle troposphere, and the atmospheric circulation is relatively stable and unchangeable. The westerly circulation in the mid-latitudes is straight, and frequent shortwave activities provide cold air conditions for the Yangtze-Huaihe region. The western Pacific subtropical high has a significant westward and northward jump, and the warm and humid airflow is transported from the edge of the subtropical high to the Yangtze-Huaihe River Basin.

The cause of the rainy season.

1. The cause of the rainy season.

1.In the high latitudes of Asia, there is a blocking high or stable ridge of high pressure in the middle troposphere, and the atmospheric circulation is relatively stable and unchangeable.

2.The westerly circulation in the mid-latitudes is straight, and frequent shortwave activities provide cold air conditions for the Yangtze-Huaihe region.

3.The 500 hPa subtropical high ridge is stable between 20 degrees and 25 degrees north latitude, and the warm and humid airflow is transported from the edge of the subtropical high to the Yangtze-Huaihe River Basin. Under such circulation conditions, the Meiyu front lingers in the Yangtze-Huaihe River basin and is often accompanied by a southwest vortex and shear line, and is active in the mesoscale system above the Meiyu front.

It not only maintains the continuous precipitation during the rainy season, but also provides abundant moisture for the heavy rain.

2. Special circumstances of rainy season.

1.Normal plum rain: The normal plum rain in the middle and lower reaches of the Yangtze River starts in mid-June and ends in mid-July, that is, it occurs in the two solar terms of "mangzhong" and "summer solstice". The rainy season lasts about 20-30 days and receives between 200 and 400 mm of rainfall.

2.Early rainy season: In some years, the rainy season starts early, and it comes suddenly at the end of May and the beginning of June. In meteorology, the rainy season that began before the "mango" is usually referred to as the "early rainy season".

3.Late Rainy Season: Meteorological speaking, the rainy season that begins after the end of June is usually called late rainy season.

There are more opportunities for late rainy season than early rainy season. Because the solar term is relatively late when the late plum rain begins, once the warm and humid air goes north, its power is very strong, and at the same time, the solar radiation is also relatively strong, and after the air is heated, it is easy to have fierce convection, so the late plum rain often has many thunderstorms and showers.

: A long strip of rain is formed. If the cold air is stronger, the rain band will move southward; If the warm air is stronger, the rain bands move northward. But in early summer, it is in the middle and lower reaches of the Yangtze River.

There's too much precipitation.

The pattern of rain bands slips smoothly as follows:

In the south of the Yangtze River in June, in June, between the Jianghuai and Huaihe rivers, in the northeast of China, the middle and lower reaches of the Yangtze River are drought. In September, it returned to the south bank of the Yangtze River, and in October, it withdrew from the South China Sea.

The seasonal pattern of the rainy season is as follows: the rain band lingers in southern China; In June, the rain belt moved to the Yangtze River basin and lingered between the Yangtze River and the Huaihe River for about a month, forming a month-long plum rainy season. In July, the rain band began to advance northward, reaching the North China Plain and the Northeast Plain in July and August. After that, it continued to move south, and then withdrew from the mainland.

Movement of frontal rain bands in China:

From winter to summer, the location of the precipitation belt gradually shifts northward: approximately.

In April and May, the summer monsoon made landfall in South China (the rainy season began); In June, the cold and warm air masses held each other in the Jianghuai region for about a month, forming a quasi-stationary front of the plum rain; In July and August, the frontal rain band moved to North China and Northeast China (drought weather occurred in the middle and lower reaches of the Yangtze River).

From summer to winter, it moves southward: in September, the frontal rain band retreats southward, and the rain band is mainly in southern and southwestern China; In October, the summer monsoon completely withdrew from the mainland of our country (the rainy season ended); In July and August, the frontal rain band moved to North China and Northeast China (the middle and lower reaches of the Yangtze River experienced drought in Helafu).

At the beginning of summer every year, the winter and summer winds in the middle reaches of the Yangtze River are evenly matched, and this rain lingers here, and the rain lasts for as long as a month.