Which weather system is a low-pressure area with winds circulating counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere?

• A. Tornado
• B. Cyclone
• C. Hurricane
• D. Anticyclone

Answer: (B)

Air moves around a low-pressure center in a cyclonic pattern, and the Coriolis effect makes that rotation take opposite directions in the two hemispheres: counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. This circulating flow around a low pressure is the defining feature of a cyclone. An anticyclone, by contrast, is a high-pressure system with the opposite rotation (clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere). Tornadoes are small, intensely rotating columns of air, not broad low-pressure weather systems, and hurricanes are tropical cyclones, a specific type of cyclone. The description given matches a cyclone most directly.