effect moving air or water is deflected horizontally because the speed of rotation of the Earth's surface is faster at low latitudes then at high latitudes. The Coriolis effect acts to the left in the southern hemisphere, imparting a clockwise swirl into an are of low pressure. There is little Coriolis effect within 7o of the equator.
Coriolis effect [for Gaspard Coriolis], tendency for any moving body on or above the earth's surface to drift sideways from its course because of the earth's rotational direction (west to east) and speed, which is greater for a surface point near the equator than toward the poles. In the Northern Hemisphere the drift is to the right of the motion; in the Southern Hemisphere, to the left. In most human-operated vehicles, continuous course adjustments mask the Coriolis effect. The Coriolis effect must be considered, however, when plotting ocean currents and wind patterns, as well as trajectories of free-moving projectiles through air or water.