Is the air pressure constant in spring, summer, autumn and winter? Reason.

Diurnal variation of atmospheric pressure

For the same area, the air pressure on the ground will be different at different times of the day, which is called the daily variation of air pressure. In a day, the atmospheric pressure on the earth's surface has a maximum and a minimum. The highest value appears at 9 ~ 10. The lowest value appears in 15 ~ 16.

There are three main reasons for the daily variation of atmospheric pressure. One is the movement of the atmosphere; The second is the change of atmospheric temperature; The third is the change of atmospheric humidity.

After sunrise, the ground began to accumulate heat, and at the same time, it transported some heat to the atmosphere, and the atmosphere also accumulated heat, and the temperature and humidity increased. When the temperature rises, the atmosphere gradually moves upward and diverges. In the afternoon 15 ~ 16, the upward and divergent velocity of the atmosphere reached the maximum, and the atmospheric humidity also reached a large value. Due to these two factors, the atmospheric pressure is the lowest at this time of the day. After 16, the atmospheric temperature gradually decreases, its humidity decreases, the ascending divergence motion weakens, and the pressure value begins to increase; Into the night; When the atmosphere cools, it begins to converge to the ground. At 9 ~ 10 in the morning, the degree of atmospheric convergence and compression is the highest, and the air density is the highest. At this time, the atmospheric pressure is the highest value in a day.

Annual variation of atmospheric pressure

In the same area, the value of atmospheric pressure is different at different times of the year. This is called the annual variation of atmospheric pressure. The annual variation of atmospheric pressure can be divided into three types, namely continental type, ocean type and mountain type. Among them, the annual variation of atmospheric pressure in ocean type is just the opposite to that in continental type. Generally speaking, "the atmospheric pressure in winter is higher than that in summer" refers to the annual variation law of atmospheric pressure in mainland China. This is briefly analyzed below (the other two situations will not be discussed).

Because the atmosphere is in the open space around the earth and has no specific boundary, it is different from the gas in a closed container. In summer, the temperature of the mainland is higher than that of the ocean, and the atmospheric humidity is relatively high (compared with winter), which makes the mainland air diffuse to the ocean continuously, leading to its pressure reduction. In winter, the temperature in the mainland is lower than that in the ocean, and the air humidity in the mainland is also lower than that in summer, which makes the air in the ocean spread to the mainland and increases the pressure in the mainland. This is why the atmospheric pressure in mainland China is higher in winter than in summer (atmospheric temperature is also a factor that affects atmospheric pressure, but the factor that determines the change of atmospheric pressure here is not temperature, but the flow and density of the atmosphere).

Changes of atmospheric pressure with climate

There are many situations in which the air pressure changes with the climate, but the most typical one is the air pressure change between sunny and cloudy days. There is a proverb called "the air pressure is higher on a sunny day than on a cloudy day", which reflects the changing law of this air pressure.

Under normal circumstances, the ground continuously radiates long waves to the atmosphere effectively, and the atmosphere is also constantly radiating back to the ground. On sunny days, the heat on the ground can be transported to the outside through the effective radiation and upward divergence of the convective gas layer. On cloudy days, clouds reduce the outward divergence of troposphere atmosphere. The effect of clouds on preserving the surface and heating the liquid layer is called "greenhouse effect". In this way, the atmospheric expansion in cloudy areas is more intense, which leads to the lateral outward diffusion of the atmosphere in cloudy areas and reduces the density of air. At the same time, the atmospheric humidity in cloudy areas is high, which also reduces the density of the atmosphere. Due to these two factors, the air pressure on cloudy days is lower than that on sunny days.