Why is the air pressure low in summer and high in winter?

If the pressure center or pressure zone is formed due to thermal reasons, high temperature will form low pressure, such as equatorial low pressure and Indian low pressure. Low temperature forms high pressure, such as polar high and Mongolia-Siberia high.

If it is a pressure center or pressure zone formed by dynamic reasons, the pressure level is not necessarily related to the temperature. Such as subtropical high and subtropical low.

Thermal expansion and cold contraction, low temperature in winter, high air density and high air pressure, high temperature in summer, low air density and low air pressure.