Definition of rainstorm

Regulation: 12 hour rainfall of more than 30 mm, or 24 hours rainfall of more than 50 mm is called rainstorm.

Heavy rain, also known as rainstorm and storm, refers to the rain that accumulates huge rainfall in a short period of time, and its value varies according to different geographical locations. Generally, it refers to the precipitation with hourly rainfall greater than16mm, or12h continuous rainfall greater than 30mm, or 24h continuous rainfall greater than 50mm. It may be caused by a typhoon. Rainstorms often cause disasters, such as floods and landslides.

Formation condition

The formation process of rainstorm is quite complicated. Generally speaking, sufficient and continuous water vapor, strong and lasting upward movement of airflow and instability of atmospheric structure 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 in arid and semi-arid areas will also cause short-term and small-scale heavy rains. Rainstorms often fall from cumulonimbus clouds. The condition for the formation of cumulonimbus clouds is that the atmosphere contains enough water vapor, and there is a strong upward movement to transport the water vapor rapidly upward. The water droplets in the cloud are constantly affected by the upward movement until the upward airflow can't support them, and they drop sharply to the ground.