Why is it half sunny and half rainy?

It's simple. When it rains, the sun is obscured by clouds. There is a sun on a sunny day ... there is also a sun on the embankment ... just don't rain ... there is no sun in the field. So the answer is: the sun. Because this is a natural law and cannot be changed. I can honestly tell you that there will be a rainbow after the storm, and the clouds in the clear sky will be very thin, so the short-wave radiation of sunlight is not scattered, and the short-wave radiation is blue-purple, so the sky is blue. When sunlight enters the atmosphere, it will scatter when it meets atmospheric molecules and particles suspended in the atmosphere. These atmospheric molecules become the light source of scattered light. They shine in all directions. In the solar spectrum, light waves with shorter wavelengths such as violet, blue and cyan are most easily scattered by atmospheric molecules and particles. Light waves with longer wavelengths such as red, orange and yellow have the strongest transmittance and can penetrate atmospheric molecules and keep their original direction. In this way, light waves are separated and colors appear.