What is the origin of rain in the 24 solar terms?

Rain is one of the twenty-four solar terms. There are four seasons in a year, three months in spring, summer, autumn and winter, and two solar terms in each month. Each solar term has its own unique meaning. The meaning of rain solar term is that rainfall begins and gradually increases. Wu Cheng's book "Twenty-four Solar Terms" in the Yuan Dynasty said: "The first month is aquatic in the sky, and spring is wood. However, people who grow trees must have water, so it rained successfully in beginning of spring. If the east wind melts, it will disperse into rain. " Rain has two meanings, one is that the weather gets warmer and the precipitation increases gradually, and the other is that there is less snow and more rain. In Yizhoushu, there are phenological descriptions such as "Hongyan coming" and "vegetation sprouting" after the rain.

Rain solar term means the beginning of rainfall, but the rainfall level is mainly light rain or Mao Mao rain. In rainy and solar terms, the direct point of the sun is gradually approaching the equator from the southern hemisphere. At this time, the sunshine hours and intensity in the northern hemisphere are increasing, and the temperature is rising rapidly. Warm and humid air from the ocean becomes active and gradually pushes northward. At the same time, cold air is not to be outdone in the weakening trend, and it frequently competes with warm air to form rainfall.