Why is the air pressure lower on a sunny day than on a rainy day?

Because there is more moisture in the air on rainy days and the molecular weight of water (18) is less than the average molecular weight of air (29), the air density on cloudy days is relatively small. And the atmospheric pressure is related to the air density. The density of atmospheric pressure is high, and the density of small air is low, so Rainy weather lowers the pressure by 1. The reason why atmospheric pressure is generated: The atmosphere is as fluid as liquid, and both are affected by gravity due to the attraction of the earth. Therefore, the atmosphere around the earth also exerts pressure on the objects immersed in it. This pressure is called atmospheric pressure. Strong. The famous Magdeburg Hemisphere Experiment in history proved the existence of atmospheric pressure. 2 The value of atmospheric pressure can be measured using Torricelli's experiment. The value of 1 standard atmospheric pressure is equal to the pressure generated by a 760 mm high mercury column, which is 1.01 ×10 5 Pascal.3 Changes in atmospheric pressure (1) The higher it is from the ground, the thinner the air and the smaller the density of the air. Within an altitude of 2000 meters, it can be approximately considered that for every 12 meters of altitude increase, the atmospheric pressure decreases by 1 mm of mercury. .(2) Generally, the atmospheric pressure on a clear day is higher than that on a cloudy day, and the atmospheric pressure in winter is higher than that in summer. The atmospheric pressure is related to the density of the air. The density of water vapor is less than that of air (mainly depends on the two main components of nitrogen and oxygen). The air on cloudy days There is more water vapor in the air, so the air pressure becomes lower! Although the air is a mixture containing a variety of gases, it can be simply divided into two parts: water vapor and other dry air without water vapor. When considering atmospheric changes as quasi-static process and there is no heat exchange, that is, regardless of the formation of clouds, fog, rain, snow, etc., the atmospheric pressure is the sum of the pressures generated by these two parts, which is the sum of the weight of water vapor and the weight of dry air in the above-mentioned air column.