Is the air pressure high or low on cloudy days?

I found several references for you, and the simplest explanation is:

There is more water in cloudy air, and the molecular weight of water is 18, which is less than the average molecular weight of air, so the air density on cloudy days is relatively small. And atmospheric pressure is related to air density, which is high in atmospheric pressure and low in density, so it is cloudy.

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If you are interested, you can also look at the following more detailed explanation:

Why is the cloudy weather low and the air pressure high on sunny days? (Li Shouli) 27-3-14 19:14 Why is the cloudy weather low and the air pressure high on sunny days? (Li Shouli)

What we usually call the atmosphere is the whole air layer around the earth. Besides nitrogen, oxygen, carbon dioxide and other gases, it also contains water vapor and dust. We call air with little water vapor (i.e. low humidity) "dry air" and air with more water vapor (i.e. high humidity) "wet air". Don't think it is "dry". The molecular weight of dry air is 28.966, while that of water vapor is 18.16, so dry air molecules are heavier than water vapor molecules. Under the same conditions, the density of dry air is also higher than that of water vapor, which is only about 62% of that of dry air. < P > However, for dry air and wet air under the same conditions, the molecular density and average mass of gas molecules in dry air are higher than that of wet air. And the average momentum of dry air molecules is also greater than that of wet air, so the pressure of dry air with low humidity is greater than that of wet air with high humidity. Cloudy air is wet and sunny air is dry, so cloudy weather is low and sunny air pressure is high.

Because the total amount of atmosphere on the earth is basically constant, when the temperature in one area increases, it is often accompanied by the temperature decrease in another area, which makes it possible for the air in the high temperature to diffuse to the low temperature. The result of diffusion is often that the air pressure in the high temperature is lower than that in the low temperature. When the northern hemisphere where we live is the midsummer that receives the most solar heat, the southern hemisphere is the severe winter that receives the least solar heat. Because the air in the northern hemisphere will diffuse to the southern hemisphere, the air pressure in the northern hemisphere is lower than that in the southern hemisphere. However, because the total amount of atmosphere is basically unchanged, the air pressure in the northern hemisphere will be lower than the standard atmospheric pressure, and the air pressure in the southern hemisphere will of course be higher than the standard atmospheric pressure. Similarly, the air diffusion in the opposite direction will make the air pressure in the northern hemisphere higher than the standard atmospheric pressure in winter. Therefore, the atmospheric pressure in the northern hemisphere will be higher than that in summer.

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