1. (Also called circumpolar westerlies, circumpolar whirl, countertrades, middle-latitude westerlies, polar westerlies, subpolar westerlies, subtropical westerlies, temperate westerlies, zonal westerlies, westerly belt, zonal winds.) Specifically, the dominant west-to-east motion of the atmosphere, centered over the middle latitudes of both hemispheres. At the earth's surface, the westerly belt (or west-wind belt, etc.) extends, on the average, from about 35° to 65° latitude. At upper levels, the westerlies extend farther equatorward and poleward. The equatorward boundary is fairly well defined by the subtropical high pressure belt; the poleward boundary is quite diffuse and variable. Especially in the Northern Hemisphere, even the annual average westerlies are markedly enhanced in some regions, namely, the jet streams. See polar vortex, antitrades, tropical easterlies, zonal index. 2. Generally, any winds with components from the west. 3. See equatorial westerlies.
Usually applied to the broad patterns of persistent winds with a westerly component. It is the dominant persistent atmospheric motion, centered over the midlatitudes of each hemisphere. Near the earth's surface, the westerlies extend from approximately 35 to 65 degrees latitude, while in the upper levels they extend further polarward and equatorward.
The Westerlies are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. The winds are predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere. Together with the trade winds, the westerlies enabled a round-trip trade route for early European sailing ships.
