What factors determine the magnitude of atmospheric pressure?

Simply put, atmospheric pressure is the mass (weight) of air per unit area perpendicular to the ground at a certain point (measurement point). This is easy to understand. The outer surface of the atmosphere surrounding the earth's atmosphere is If it is round, the higher the altitude of a certain point on the earth, the shorter (lighter) the air column above it and vice versa

But the reason why the atmospheric pressure at a certain point on the earth does not change constantly is that The mass (weight) of the upper air column is changing, and the reason for the change in weight is the flow of the atmosphere. When the air with a lower temperature flows over, the atmospheric pressure will increase; when the air with a higher temperature flows over, the atmospheric pressure will decrease. This is because the density (weight) of the atmosphere with high temperature is small, and the density (weight) of the atmosphere with low temperature is large.

It is precisely because of changes in atmospheric pressure (the flow of the atmosphere) that there are weather changes such as bright sunshine and dense clouds. Therefore, atmospheric pressure is an extremely important data indicator in weather forecasting. We all have this experience: the weather is sultry in summer, and swallows will fly to higher places. This is because the sultry heat causes the air near the surface to be less dense (fewer gas molecules per unit volume) and slightly deprived of oxygen, so do you feel stuffy? Swallows can fly, so they have to go to high places, because the temperature there is lower (for every 1,000 meters above the surface, the temperature will drop by 5-6 degrees Celsius) and the density of the air is higher.

The International System of Units for pressure is Newton/square meter

Atmospheric pressure is generally expressed in bar (bar) - kilogram force/square centimeter; millibars (mbar) are also commonly used. One thousandth of a bar