Heavy rain refers to rain with high precipitation intensity, which is often formed in cumulonimbus clouds. According to China's meteorological regulations, heavy rainfall with 24-hour precipitation exceeding 50 mm is called "rainstorm". According to its precipitation intensity, it is divided into three grades, namely, 24-hour precipitation of 50-99.9 mm is called "rainstorm", 100-250 mm is called "heavy rainstorm", and more than 250 mm is called "extraordinary rainstorm".
The world's largest rainstorm occurred in Reunion Island in the South Indian Ocean, with a 24-hour precipitation of 1.870 mm, and the largest rainstorm in China occurred in Xinliao, Taiwan Province Province, with a 24-hour precipitation of 1.672 mm, all caused by tropical cyclone activities. China is one of the countries with the most rainstorms in the world, and almost all provinces (cities, districts) have rainstorms. Mainly concentrated in the summer half year. The regional distribution of rainstorm days is obviously more in the south and less in the north; There are many coastal areas and few inland areas; There are many windward slopes and few leeward slopes.
Types of rainstorm
1. Stable meridional pattern: In this flow pattern, the westerly belt is dominated by meridional circulation, and the long-wave system moves slowly or stagnates. The subtropical high is also relatively stable, but it is located in the north. In this case, the mid-low latitude system can easily interact with each other. Stable meridional rainstorms are often the most serious, and some famous rainstorms in China's history have occurred under this circulation.
2. Stable zonality: the second is stable zonality. At this time, zonal circulation prevails in the westerly belt of 35 ~ 55 N, with more short-wave trough activities, and the subtropical high is relatively stable, often zonal.
3. Transitional type: The main feature of transitional type is the unstable position of subtropical high. During the rainstorm, the subtropical high often advances and retreats obviously. The westerly circulation is a moving system, and the precipitation time is relatively short, and the intensity is not as great as that of the first and second types.