Why is sunny weather low pressure?

Generally speaking, areas with high ground pressure are often sunny, and areas with low ground pressure are often rainy. The high pressure and low pressure mentioned here are relative, not the absolute value of atmospheric pressure. The air pressure in a certain area is higher than that in the surrounding area, which is called high pressure area; The air pressure in a certain area is lower than the surrounding air pressure, which is called low pressure area.

On the same horizontal plane, if the air pressure distribution is uneven, the air will flow from the high pressure area to the low pressure area. Therefore, the air pressure in a certain area is high, and the air in this area flows out in the horizontal direction. The air above the high pressure area will drop. Because the atmospheric pressure increases with the decrease of altitude, when the air at high altitude falls, the pressure is increased, the volume is decreased, the temperature is increased, and the condensate in the air evaporates and dissipates.

Therefore, the high-pressure central area is not conducive to the formation of clouds and rain, and it is often sunny. If the air pressure in a certain area is low, the air in the surrounding area will flow into the area horizontally, causing the air in the area to rise, the rising air will expand due to the pressure drop, the temperature will drop, and the water vapor in the air will condense. Therefore, it often rains in the central area of low pressure.

The relationship between atmospheric pressure and altitude is:

With the increase of height, the atmospheric pressure decreases; In the range of 3000M, every time the air pressure increases 12M, the air pressure decreases 1mmHg, which is about 133Pa.

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.

Refer to the above? Baidu encyclopedia-low pressure weather