The Highs and Lows of Air Pressure





High atmospheric pressure and low atmospheric pressure

The cause of wind blowing is the difference in air pressure.

A high pressure system has higher pressure at its center than the areas around it. Wind blows away from high pressure. Winds of a high pressure system swirl in the opposite direction as a low pressure system – clockwise north of the equator and counterclockwise south of the equator. This is called anticyclonic flow. Air from higher in the atmosphere sinks down to fill the space left as air blew outward. On a weather map the location of a high pressure system is labeled with a blue H.

A low pressure system has lower pressure at its center than the areas around it. Winds blow towards the low pressure, and the air rises in the atmosphere where they meet. As the air rises, the water vapor within it condenses forming clouds and often precipitation too. Because of Earth’s spin and the Coriolis Effect, winds of a low pressure system swirl counterclockwise north of the equator and clockwise south of the equator. This is called cyclonic flow. On weather maps a low pressure system is labeled with red L.