Why is it rainy and foggy in Yunguichuan Basin?

1 1. Because of the basin topography, and Sichuan is located in the south of Huaihe River in Qinling Mountains, the climate is mild and humid, the air is full of moisture, the temperature is high, and the air sinks, so it is foggy. Because of the cloud cover, the sun can't shine directly, so the temperature in Sichuan is low during the day, and it is higher than that in the same latitude area at night because of the strong reverse radiation of the atmosphere. Physically, the gravity of the earth produces atmospheric pressure, just like in water. The greater the underwater pressure, the stronger the compressibility of gas, so the lower the air pressure, the smaller the volume. The lower the pressure, the larger the volume and the smaller the density.