May 02, 2002
As air moves from high to low pressure, its motion is affected by the rotation of the Earth. The Coriolis force causes converging air to rotate in a cyclonic direction - counterclockwise in the northern hemisphere, and clockwise in the southern hemisphere. This effect is illustrated in the images above. In the upper image, Hurricane Olga is seen churning counterclockwise in the Atlantic Ocean on November 28 last year (the same direction as the rotation of the Earth as viewed from the North pole). A low pressure system south of Australia is seen to be rotating in a clockwise direction in the lower image from February 20 of this year, in the same direction as the Earth's rotation as seen from the South pole. Although the scale of the rotational features is different, the overall shape and direction of rotation are good examples of the physics of air motion on a rotating sphere. See the links below for why this works. Thanks to Norman Kuring for making these great SeaWiFS examples available!