What kind of weather system caused the precipitation in China, what kind of precipitation was formed, and what kind of meteorological disasters were produced?

Weather system usually refers to the atmospheric motion system of meteorological elements such as temperature, air pressure or wind that causes weather changes and has certain spatial structure characteristics. If some are characterized by spatial pressure distribution, they are composed of high pressure, low pressure, high pressure ridge and low pressure trough. Others are classified according to the distribution characteristics of wind, such as cyclone, anticyclone and shear line. Some are determined by the characteristics of temperature distribution, such as front; Others are classified according to certain weather characteristics, such as thunderstorms and tropical clouds. Usually, there is a certain configuration relationship between meteorological elements such as air pressure, wind and temperature that constitute a weather system.

The weather systems that cause precipitation in China are as follows:

1, front:

The front is a narrow transition zone formed by the meeting of cold and warm air in the near-surface layer. According to the moving direction and structure of cold and warm air masses on both sides of the front, the front can be generally divided into four types: cold front, warm front, quasi-static front and blocking front.

Cold front can be divided into two types according to the moving speed, one is cold front and the other is cold front. The first kind of cold front (slow moving cold front) moves slowly, and the front slope is small (about1100), resulting in a layered cloud system similar to a warm front, but the distribution order of the cloud system is opposite to that of the warm front, and the cloud system and rain area are mainly located behind the ground front. Because the front slope is greater than the warm front, the cloud area and rain area are narrower than the warm front, and the precipitation is more stable. The second cold front (fast cold front) moves fast and has a large slope (1/40— 1/80). The cold air mass behind the cold front is powerful and moving fast, which violently impacts the warm air, making the warm air rise rapidly, forming a narrow range of cumulus clouds arranged along the front, resulting in convective precipitation weather. In summer, the air is heated unevenly and has strong convection. When the cold front moves, there are often strong winds, dark clouds, heavy rains and lightning, and the meteorological elements change dramatically. However, this kind of weather lasted for a short time. After reaching the front line, the temperature dropped sharply and the weather suddenly became sunny.

Warm front precipitation mainly occurs in the middle of nimbostratus, mostly continuous precipitation. There are few obvious warm fronts in China, and most of them are accompanied by cyclones. In spring and autumn, it generally appears in the Jianghuai Basin and Northeast China, and it mostly appears in the Yellow River Basin in summer.

The cloud area and precipitation area of the quasi-static front are wider than those of the warm front, and the precipitation intensity is relatively small, but it lasts for a long time, which may cause continuous rain and cloudy weather in Mao Mao. For example, the plum rains in the middle and lower reaches of the Yangtze River from June to July every year are partly due to the fact that the quasi-static front in South China moves northward to the middle and lower reaches of the Yangtze River, resulting in long-term precipitation.

The occlusion front is formed by merging two moving front edges. So its weather still retains the weather characteristics of the original two fronts.

2. Cyclone:

Cyclone refers to the large vortex in which the horizontal airflow rotates counterclockwise (clockwise) in the northern (southern) hemisphere atmosphere. At the same height, the air pressure in the center of the cyclone is lower than that around it, which is also called low pressure. Because the airflow flows into the cyclone center from all directions, it forces the central airflow to rise and condense into rain. Therefore, when cyclones cross the border, the cloud cover increases, and rainy weather often occurs, that is, cyclone rain.

Usually classified according to the main areas or thermal structures where cyclones are formed and active. According to the region, it can be divided into tropical cyclone, temperate cyclone and polar cyclone vortex According to the thermal structure, it can be divided into cold air rotation and hot low pressure.

Most of our country is temperate zone, which belongs to the intersection of north and south airflow, and cyclone rain is extremely developed. Cyclones in China mostly occur in the eastern part of the plateau, and there are Mongolian cyclones, northeast low pressure and Yellow River cyclones in the north. The proportion of cyclone rain is above 60% everywhere, over 80% in Central China and North China, and even 70% in the northwest inland.

3. Frontal cyclone:

Surface cyclone and frontal cyclone, collectively referred to as frontal cyclone, are common weather systems in the middle and high latitudes of northern China. Because the airflow flows into the cyclone center from all directions, it forces the central airflow to rise and condense into rain. Therefore, when cyclones cross the border, the cloud cover increases, and rainy weather often occurs, that is, cyclone rain. In the frontal weather system, whether it is a cold front or a warm front, the warm air mass above the frontal surface rises along the frontal surface, which will form cloudy and precipitation weather, that is, frontal rain. When the two systems combine to form a frontal cyclone, it will converge into a stronger updraft, and the weather will change more violently, often causing clouds, rain and even heavy rain, thunderstorms and windy weather. Jianghuai cyclone is a frontal cyclone that occurs in Jianghuai basin and Hunan and Jiangxi areas. It occurs frequently in spring and summer, especially in June and July during the Meiyu period, which is one of the important weather systems that cause heavy rain in Jianghuai area.

4. Shear line:

Shear line usually refers to the discontinuous line of wind direction or wind speed of 700 hectopascals and 850 hectopascals, which is actually the dividing line between two opposite airflow. It is formed because the northern part of the trough moves fast and the southern part moves slowly. The airflow on the shear line is a cyclone circulation with obvious horizontal convergence, which is conducive to upward movement and easy to produce rainy weather. The middle and lower reaches of the Yangtze River are most prone to shear lines, and areas with abundant water vapor supply are prone to heavy rain.

Cyclone shear line appears all year round in China's plains and plateaus, and it is the most frequent in late spring and early summer, and it is one of the main precipitation weather systems. According to the type of wind field, it can be divided into cold front, warm front, quasi-static front and north-south shear. The distribution of precipitation on the shear line is very uneven, and heavy rains often appear in areas with strong convergence and sufficient water vapor supply. The eastward movement of southwest vortex along shear line is often the main reason for enhancing convergence.

The location of the shear line affecting the upper air in China is closely related to the activity of the subtropical Pacific high. In spring, the subtropical Pacific ridge line is located in the south of 20 N, forming a shear line in South China, which is called the South China shear line. From June to July, the Pacific subtropical high moved northward, and its ridge line was between 20 N and 25 N, forming a shear line in the Jianghuai basin, which was called the Jianghuai shear line. Under its control, it often produces heavy rain and thunderstorms, which is an important weather system for precipitation in Meiyu period in Jianghuai area. From mid-July to mid-August, the ridge line of subtropical high is between 25 N and 30 N, forming a shear line in North China, which is called the North China shear line. In winter, when westerly jet meets the Qinghai-Tibet Plateau, it is divided into two streams, the south and the north. The shear line formed by the confluence in the eastern part of the Plateau is an important weather system affecting the vast southwest.

5. Typhoon:

Typhoon is a kind of tropical cyclone. A tropical cyclone with a sustained wind speed of 12 to 13 (that is, 32.7m to 41.4m per second) is called a typhoon or hurricane. Tropical cyclone is a low-pressure vortex that occurs on the surface of tropical or subtropical ocean, and it is a powerful and profound tropical weather system.

Typhoon is a disastrous weather system with strong destructive power, and it is one of the weather systems that bring heavy rain. The area where the typhoon passes may produce rainfall of 150 mm ~ 300 mm, and a few typhoons can directly or indirectly produce heavy rain above 1000mm, such as the heavy rain in southern Henan after the (indirect) 1975 tropical cyclone landed, which broke the rainfall records in some areas.

Typhoon often brings stormy weather when crossing the border, causing huge waves on the sea surface, which seriously threatens the safety of navigation. After the typhoon landed, the storm surge may destroy crops and various building facilities, causing great losses to people's lives and property.

6, cut off the low pressure:

Cut-off depression is a cold air rotation in the upper and middle troposphere. It is a cold depression, sometimes called a cold vortex, which is formed by the rapid southward movement of the cold air pile at the southern end of the low-pressure trough in the middle and upper troposphere, and being cut off from the main body of the northern cold region by warm air on both sides. Cut off the updraft prevailing in the low-pressure area. The strongest updraft is in the east, which is generally rainy in the east and sunny in the west. Cut-off low pressure has regional and seasonal characteristics, and typical cut-off low pressure is rare in China. Only in the northeast, a cold vortex is common in summer, which is similar to cutting off the low pressure. Although this cold vortex has a weak circulation and a small range, it often produces heavy rain.