About the daily variation of air pressure? People with certain geographical knowledge will answer.

The diurnal variation of surface pressure has the form of single peak, double peak and three peaks, of which the double peak type is the most common, which shows that there is a highest value, a second highest value, a second lowest value and a second lowest value in one day. Generally, the air pressure rises in the morning, with the highest value at 9- 10, and then drops, with the lowest value at 15- 16, and then gradually rises, with the second highest value at 2 1-22, and then drops again, with the second lowest value at 3-4 the next day. The time and range of the highest and lowest values vary with latitude, and the diurnal variation of air pressure in tropical areas is the most obvious, with a daily range of 3-5 hectopascals. With the increase of latitude, the diurnal range of air pressure decreases gradually, and the diurnal range to latitude 50 has decreased below 1hPa.

The reasons for the daily variation of air pressure are very complicated, and there is no explanation from the staff at present. Generally speaking, it is closely related to the daily variation of temperature and atmospheric tides. For example, the daily fluctuation of air pressure (single peak type) has a great relationship with the daily change of temperature. When the temperature is the highest during the day, the lower air rises due to thermal expansion, rises to the upper air and spreads around, resulting in ground decompression. When the temperature is the lowest in the morning, the air cools and contracts, and the air pressure correspondingly rises to the highest value. It is only because the influence of temperature on air pressure takes some time that the extreme value of air pressure appears behind the temperature. At the same time, the daily variation range of air pressure varies with land, sea, season and terrain, which shows that land is greater than sea, summer is greater than winter, and valley is greater than plain. The semidiurnal wave (double peak) of atmospheric pressure may be related to the whole semidiurnal vibration cycle of the atmosphere caused by the alternation of cold and warm during the day, and may also be related to the atmospheric tides caused by the sun and the moon. As for the three-peak pressure wave, it seems to be related to the comprehensive action of diurnal wave, semidiurnal wave and local topographic conditions.

I picked the above content from the professional course book, which is probably the case. It seems that there is no accurate conclusion.

Meteorology and Climatology (3rd Edition), edited by Zhou Shuzhen Higher Education Press, July 1997.

Wu Guanghe's physical geography has many contents and is comprehensive, but many of them are simply mentioned without narration and analysis. It is a compressed version of all professional courses of physical geography for geography majors. If you want to know more, you should read some books in the departments below physical geography. I recommend the old version, but the new version doesn't seem to be detailed. If you have any questions, you can call me. I hope I can help you.