Clouds composed of liquid water droplets (including supercooled water droplets) are called water clouds. If the conditions for cloud droplets to grow into raindrops are met in the water cloud, and the raindrops have a certain falling speed, then it is rain or Mao Mao rain that falls. Clouds composed of ice crystals are called ice cloud, and clouds composed of water droplets (mainly supercooled water droplets) and ice crystals are called mixed clouds. Ice crystals or snowflakes falling from ice cloud or mixed clouds fall into the gas layer above 0℃, and after melting, they will also fall to the ground in the form of raindrops, forming rainfall.
In the process of rain formation, large water droplets play a very important role. When the radius of water droplets increases to 2 ~ 3 mm, the attraction between water molecules is difficult to maintain such a large water droplet, and it is easy to be split by the impact of airflow on the way down. Through the "chain reaction", the big raindrops continue to split, and the small raindrops continue to fall, forming new big raindrops. This is an important reason for the formation of rain in water clouds and mixed clouds with strong updraft.