The daily variation of atmospheric pressure is characterized by a maximum value and a secondary high value, a minimum value and a secondary low value in a day. The highest value appears at 9-10, and the second highest value appears at 21-22; The lowest value occurs at 15~16, and the second lowest value occurs at 3~4.
The diurnal variation of atmospheric pressure is more obvious in low latitude areas. The daily amplitude of atmospheric pressure (the difference between the highest and lowest values in a day, also known as the daily range) decreases with the increase of latitude. In the low latitude area, the average daily amplitude can reach 3~4 hPa, and the daily amplitude near the latitude of 50 degrees is less than 1 Pascal Has. The daily amplitude of atmospheric pressure in different latitudes ranges from 1 to 2.5 hPa in the middle latitudes of China, 2.5 to 4 hPa in the low latitudes, and sometimes up to 6 5 hPa. There are three main reasons for the daily change of atmospheric pressure: first, the movement of the atmosphere; The second is the change of atmospheric temperature; Third Atmospheric humidity Changes. After sunrise, the ground begins to accumulate heat, and at the same time, the ground transmits part of the heat to the atmosphere, which also continuously accumulates heat, and its temperature rises and humidity increases. When the temperature rises, the atmosphere gradually makes upward divergent movement towards the upper air. At 15~16 p.m., the speed of atmospheric upward divergent movement reaches the maximum, and the atmospheric humidity also reaches a larger value. Due to the influence of these two factors, the atmospheric pressure at this time of the day is the lowest. After 16:00, the atmospheric temperature gradually decreased, its humidity decreased, the upward divergent movement weakened, and the atmospheric pressure began to increase. At night, the atmosphere becomes cold and begins to move toward the ground convergence The atmospheric divergence decreases and compresses to the maximum extent at 9~10 a.m, Air density The atmospheric pressure is the highest in a day. [1] 
