Focus on
Circulation Around Lows and Highs

Low Pressure System

High Pressure System

The diagrams above illustrate the flow of air around areas of low and high pressure in the Northern Hemisphere. As air enters an area of low pressure from all directions, the Coriolis effect bends the direction of the to the right of its path. This creates a counterclockwise rotation around the low as it convergences toward the center of the system. As the air collides near the center it is forced aloft where it divergences away from the center. The divergence is necessary for the system to be maintained as an area of low pressure. Without divergence aloft the system would fill with air and the horizontal pressure difference would be equalized causing the system to dissipate.

For high pressure areas, air descends toward the surface with convergence of air aloft. As the air nears  the surface it is forced outward (divergence) from the center. The Coriolis effect bends the air to the right of its path creating a clockwise rotation around the high.

Because the Coriolis effect works in the opposite direction in the Southern Hemisphere, circulation around lows are clockwise and inward toward the center at the surface and highs exhibit a diverging, counterclockwise rotation.

Back to Atmospheric Circulation Lecture Outline