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

Because when the sun reaches the ground on a sunny day, the heat is large, and the ground gas is heated and expanded, and the pressure line will bulge upward, and the air pressure will be high. This is a fact. On cloudy days, due to the cloud cover, the heat reaching the ground is less, the ground temperature is lower, and the gas will contract when it is cold, so the pressure line is concave downward and the pressure is lower.