Why is the air pressure high on sunny days and low on cloudy days?

Differences between atmospheric circulation and atmospheric pressure system.

The reason why the air pressure is high in sunny days and low in cloudy days lies in the difference of atmospheric circulation, that is, the air pressure system. On sunny days, the air pressure system is a high-pressure system, and the air sinks and spreads around, forming a high-pressure state; On cloudy days, the air pressure system is a low-pressure system, and the air rises, causing more water vapor and clouds, forming a low-pressure state.

Air pressure refers to the air pressure per unit area, usually in Pascal (Pa). On the surface of the earth, due to the existence of the atmosphere, the atmospheric pressure at different heights and places is different, and the standard atmospheric pressure (10 1325 Pa) is usually taken as the reference value.