Water is the foundation of all kinds of life on the earth, and its changes and movements have created our world today. On the earth, water is constantly circulating. The water in the ocean and on the ground is heated and evaporated into the sky. The water vapor moves to other places with the wind. When they encounter cold air, they form precipitation and return to the earth's surface. There are two kinds of precipitation: one is liquid precipitation, which is rain; The other is solid precipitation, which is snow or hail.
Snowfall mostly comes from nimbostratus and high-level clouds, and the precipitation intensity changes slowly; Cumulonimbus clouds snow in cold days and have the characteristics of showers, which are called snow showers.
Snowfall consists of a large number of snow crystals of different sizes, and generally there are many smaller ones. In order to describe the particle size distribution characteristics of falling snow crystal population, snow crystal spectrum or solution spectrum after snow crystal melting is often used.