Meteorology An atmospheric system characterized by the rapid inward circulation of air masses about a low-pressure center, usually accompanied by stormy, often destructive weather. Cyclones circulate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Meteorology A violent tropical storm, especially one originating in the southwestern Pacific Ocean or Indian Ocean. A violent rotating windstorm. Any of various devices using centrifugal force to separate materials.