What is air pressure? How to distinguish between high pressure and low pressure?

Air pressure is the density of air, which is the density of air.

The more air molecules, the higher the air pressure.

Usually, the air pressure near the ground is high, and the farther away from the ground, the lower the air pressure.

In the atmospheric circulation diagram, the direction of the arrow is from high pressure to low pressure, which can be well understood from the formation diagram of pressure zone and wind zone.

Usually 1000 hectopascals can be considered as high pressure, and 500 hectopascals can be considered as low pressure.

But high pressure and low pressure are relative, because air is constantly flowing, and the direction is from high pressure to low pressure, which is the direction indicated by the arrow.

Therefore, in a thermodynamic cycle diagram, as long as you know the arrow, you can know its relative high pressure and relative low pressure.

Air expands and rises when heated and contracts and sinks when cooled. At the same level, cold things will become high pressure and hot things will become low pressure, so there is a saying called cold high pressure and hot low pressure.

In frontal cyclone (air convergence ascending system), the center of southern hemisphere and northern hemisphere is low pressure, so it can converge and ascend. In the anticyclone, the center of the southern hemisphere and the northern hemisphere is high pressure, so the anticyclone is a divergent system.

In the vertical direction, the cyclone rises and the anticyclone falls, and the wind direction can be known according to the frontal cyclone.

Cyclones are usually rainy and anticyclones are usually sunny.

In a word, air pressure is closely related to many weather conditions and natural phenomena.