Does the air pressure rise or fall before it rains? Why?

The reduction of atmospheric pressure is closely related to the weather. Generally speaking, the air pressure in sunny days is higher than that in cloudy days, and the air pressure in winter is higher than that in summer. Atmospheric pressure is related to altitude, atmospheric temperature and atmospheric density, and generally decreases exponentially with altitude. The air pressure changes every day and every year.

In a year, the air pressure in winter is higher than that in summer. In a day, the air pressure has a maximum value and a minimum value, which appear at 9 ~ 10 and 15 ~ 16 respectively, and the second high value and the second low value appear at 2 1 ~ 22 and 3 ~ 4 respectively.

The daily variation of air pressure is small, generally 0. 1 ~ 0.4 kPa, and decreases with the increase of latitude. The change of air pressure is closely related to wind and weather, so it is an important meteorological factor.

Measuring tools:

The most commonly used instruments for measuring air pressure are mercury barometer and empty box barometer.

Air has weight, and air pressure refers to the force exerted by the atmosphere per unit area. The so-called air pressure in a certain place refers to the total weight of the air column extending vertically upward to the top of the atmosphere.

In meteorology, hectopascals are often used as the unit of pressure measurement. Specifically, when the sea level with a temperature of 0℃ and a latitude of 45 degrees is taken as the standard, it is called 1 atmospheric pressure, and its value is 760 mm Hg, or equivalent to10/3.25 hectopascals.