Winds, Westerlies

THE WESTERLIES ARE the prevailing winds in the middle latitudes blowing from the subtropical high pressure toward the poles. The westerlies originate as a result of pressure differences between the subtropical high-pressure zone and the subpolar low-pressure zone. The westerlies curve to the east because of the Coriolis effect, caused by the Earth's rotation. In the Northern Hemisphere, the westerlies blow predominantly from the southwest, whereas in the Southern Hemisphere, they blow predominantly from the northwest. The equator-ward boundary is fairly well defined by the subtropical high-pressure belts, whereas the poleward boundary is more variable. The westerlies can be quite strong, particularly in the Southern Hemisphere, where less land causes friction to slow them down. The strongest westerly winds typically occur between 40 degrees and ...