Why do you say "sunny and foggy for a long time, foggy and sunny for a long time"

The agricultural proverb says, "It's sunny and foggy for a long time, and the fog is sunny for a long time." Practice has proved very reasonable.

We know that fog is caused by a lot of water vapor in the air. A weather phenomenon in which water vapor condenses due to temperature drop. In a place, the weather is fine for a long time. Although there is a temperature difference between day and night, the air is dry and stable, and fog will not form. Once warm and humid air moves in at night, it will form advection radiation fog. So fog appears after a long sunny day, indicating that the air in this place has become humid. Once it meets cold air, it will turn into clouds and cause rain.

On the contrary, the weather in a place is always rainy, the ground is covered with clouds, the temperature difference between day and night changes little, and fog is not easy to form. Once the cloud splits, the ground radiates heat and cools down at night, which is conducive to the condensation of water vapor and the formation of fog. Therefore, after a long rain, there will be foggy weather. After the sun appears, the fog will fade away and it will be sunny. This is why it is foggy and sunny after a long rain.