How is the rainstorm formed?

Rain with heavy rainfall intensity. The rainfall per unit time is called rainfall intensity. China's meteorological department stipulates that: 24-hour rainfall is greater than or equal to 50 mm for heavy rain; Heavy rain occurs when it is greater than or equal to 100 mm; It's a rainstorm of 200 mm or more. The world's largest rainstorm occurred in Reunion Island in the South Indian Ocean, with a 24-hour rainfall of 1.870 mm, and the largest rainstorm in China occurred in Xinliao, Taiwan Province Province, with a 24-hour rainfall of 1.672 mm. Extreme rainstorm is a disastrous weather, which often causes floods and serious soil erosion, leading to major economic losses such as engineering accidents, dike breaches and crop flooding. However, moderate heavy rain is an important source of water resources, which can be used to promote profits.

Abundant and persistent water vapor, strong and persistent upward movement of airflow and instability of atmospheric stratification are the main physical conditions for heavy rain. The favorable combination of various scales of weather system and underlying surface, especially topography, can produce heavy rain. The main weather systems that cause large-scale rainstorm in China are fronts, cyclones, shear lines, eddies, troughs, typhoons, easterly waves and intertropical convergence zone. In addition, thermal thunderstorms will also cause short-term and small-scale heavy rains in arid and semi-arid areas.

China is a rainy country. Except for some provinces and regions in the northwest, it is almost always heavy rain. Winter rainstorm is limited to the coastal areas of South China, with frequent rainstorm in South China from April to June. From June to July, persistent rainstorms often occur in the middle and lower reaches of the Yangtze River, with long duration, wide range and large amount of rainstorms. July-August is the main rainstorm season in northern provinces, and the rainstorm intensity is very strong. From August to 65438+ 10, the rain belt gradually withdrew southward. After summer and autumn, the typhoon rainstorm in the East China Sea and the South China Sea is very active, and the point rainfall of typhoon rainstorm is often very large.

In people's impressions and various literary works, rainstorm is instantaneous heavy rain, such as downpour and downpour, but in meteorology, rainstorm is the weather situation of a day. If the rainfall in a place is greater than or equal to 50mm within 24 hours, the weather here is rainstorm, and the "rainstorm" in people's impression is called short-term heavy rainfall.

Storm (full text)

I feel very honored to have the opportunity to introduce the rainstorm to you today. Today, I will systematically introduce the formation of rainstorm, the disasters caused by rainstorm, and how to monitor and forecast rainstorm, mainly introducing these contents. Rainstorm is a very important disaster in China, especially in the Yangtze River basin. Or the whole area south of Huaihe River in China. Of course, there was a big flood in the Yellow River. So in general, rainstorm is a major meteorological disaster in our country, so everyone is concerned that there was another flood in the Huaihe River Basin during the flood season in 2003, so this picture is a satellite cloud image released by Fengyun-2 meteorological satellite developed by our country, and we can see a cloud belt over the Huaihe River Basin for a long time.

So, for example, 1998, due to the flood in the Yangtze River basin, the whole country lost more than 300 billion RMB. /kloc-more than 0/000 people were killed in the flood. Therefore, flood disaster is different from drought. Flood disaster is like an acute disease, which will cause sudden losses to people's lives and property. Generally speaking, drought, like our chronic disease, affects for a long time. It will also cause great losses, but it is mainly the economy, especially agricultural production. So we can see from this table that in recent years, our country as a whole has suffered more and more losses due to meteorological disasters. With the development of China's national economy, the losses caused by meteorological disasters also increase with the development of national economy. So this is obvious from above.

We are also a flood disaster. For example, on August 5, 2006, there was a tropical cyclone in Shanghai from 1 to 10, which caused a heavy rain and flooded the whole Shanghai. So a disaster like this, if everyone knew it twenty years ago, was that several quilts were wet. But today, every family has all kinds of household appliances, and soaking in water will cause great losses. The same is true in that factory. The equipment in the factory now can't be compared with the factory decades ago. Therefore, with the development of China's national economy, the losses caused by rainstorm disasters to China's entire economy are becoming more and more serious. So this picture is caused by the flood in the Huaihe River basin, and we can see the flood in the countryside.

So it is very important to forecast the rainstorm now, because we should take measures to prevent floods. 1998 floods are a great threat to the Three Gorges Reservoir, and it is very important to make a good rainstorm forecast to ensure the construction safety of the Three Gorges Reservoir. In this process, China Meteorological Bureau has played a great role in ensuring the Three Gorges Reservoir to survive the flood. We basically guaranteed the meteorological forecast and meteorological support for the entire Three Gorges Reservoir during the flood. For example, by the end of the flood, the Three Gorges Reservoir had been greatly affected by the earth dam, that is, the dam made of soil had been soaked in the water for a long time. If there is another rainstorm exceeding 50 mm, all the machinery and equipment of the Three Gorges Reservoir will be evacuated. Personnel should be evacuated to ensure the safety of mechanical equipment and personnel. Then at this time, the Yangtze Three Gorges Corporation asked the China Meteorological Bureau to give a correct forecast. Is it possible to have another rainstorm over 50 mm later? If there is going to be a rainstorm exceeding 50 mm, all these personnel and equipment should be evacuated from the Three Gorges site. Then the National Meteorological Center correctly predicted that the precipitation would not exceed 50 mm, so the whole project could not be stopped. If all equipment and personnel are evacuated from the Three Gorges Reservoir, it is estimated that the project progress will be delayed by one year. Therefore, meteorological support, especially rainstorm forecast and disaster forecast, has played a great role in safeguarding major projects in China. However, the rainstorm forecast is not a simple matter. There are two main difficulties in rainstorm forecasting. The first rainstorm was sudden and intense. As we all know, in summer, we see a large dark cloud rising from the west. It won't be long before it rains heavily. This is what we call a rainstorm. Especially in the rainy season, it often happens, so the sudden occurrence of heavy rain has a great influence on our forecast, and the area of heavy rain is usually relatively small.

For example, let me give you an example. On July 2 1, 1998, there was a three-day rainstorm in Wuhan, with an hourly rainfall of 88.4 mm. What is the equivalent of three days' rainfall in Wuhan? I wonder if the audience here have ever been to Wuhan? There is a place called East Lake in the center of Wuhan. The water falling in three days is equivalent to 1.5 times of the water inflow of East Lake, falling over Wuhan. Then this will definitely cause water disasters in Wuhan, so from this perspective, how to forecast this rainstorm is a very difficult place. Especially its turning point, critical moment, is particularly difficult. When did it happen? Where did it happen? How strong is it? This is a very difficult thing in our meteorology and weather forecast.

The second rainstorm forecast must have happened under the background of a certain atmospheric general circulation, which is the general motion state of our atmosphere. Especially those who care about the weather forecast will always hear the so-called tropical negative high. The negative tropical high is a high pressure belt that controls our southeast coast in summer, and this high pressure has a great influence on our whole eastward airflow. To the west of this negative tropical high, there must be a southbound airflow. Moreover, this southerly airflow brings a lot of warm and humid air from the south to the north, so the change of tropical negative high pressure can make our water vapor directly sent from South China to the Yangtze River basin. This caused the cold air from the north to come over and the warm and humid air from the south to go north. When cold and warm air collide, strong convection occurs. Warm air comes, cold air goes down and warm air goes up. In this way, the warm air goes up desperately, and it is warm and wet. So in the process of rising, it cools down and becomes precipitation, and then falls down. Therefore, the whole process is a very complicated problem in dynamics, physics and thermodynamics. So this rainstorm forecast is a very difficult place. Therefore, in order to make a good rainstorm forecast, we must first do a good job of monitoring. Therefore, if we can improve the ability of rainstorm forecasting, we will actually improve the overall ability of disaster prevention and mitigation in our whole country. So how do we monitor the rainstorm? This is a matter of great concern to us.

I think the following, as far as our current scientific and technological development is concerned, I will introduce it to you. Let me first talk about how the rainstorm is formed. Generally speaking, there are three kinds of rainstorm, one is the Meiyu front rainstorm I just mentioned. The second is a typhoon, or a typhoon with low intensity. We call it a tropical cyclone. Thirdly, in summer, we often encounter heavy rain brought by convection. So we generally divide rainstorm into three types. So how did the rainstorm form? It has three main conditions. The first condition, you must have enough water vapor to form a rainstorm. The second is that you have enough steam. How is this steam sent from bottom to top? So there must be upward movement. That is, this steam must climb up. As we all know, the temperature of the lower atmosphere is relatively high, and it becomes lower in the upper atmosphere. Then, as we all know, we never said that opening the window was for flying. Why? Because when the plane flies into the sky, it is tens of degrees below zero outside the glass window. So if the plane flies in the sky, it must be sealed. It must ensure that the inside of the plane reaches the temperature and humidity comfortable for our human body. So when our warm and humid air climbs up, it condenses into water drops as soon as it meets cold. If this water drop is greater than such a supporting force caused by our upward movement, then this water drop will fall, and then a rainstorm will be formed. Therefore, the second condition must have a strong upward movement. The third condition is stability. What is stability? I just said that if our warm air is below, our cold air is above. As we all know, the proportion of cold air is large, while the proportion of warm air is small. So warm air will definitely rise and cold air will come down. This will lead to agitation in the atmosphere, and the cold will drop and the warmth will rise. After this caused a somersault, it caused a strong upward movement, because warm air had to climb up and cold air had to come down to warm the air. As soon as this warm air goes up, it will cause what I just said, and it will condense when it meets cold. When it condenses, it becomes a water drop, and when it falls, it becomes rain.