Trade winds

From Glossary of Meteorology

trade winds

  1. (Commonly called trades.) The wind system, occupying most of the Tropics, that blows from the subtropical highs toward the equatorial trough; a major component of the general circulation of the atmosphere.

    The winds are northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere; hence they are known as the northeast trades and southeast trades, respectively. The trade winds are best developed on the eastern and equatorial sides of the great subtropical highs, especially over the Atlantic. In the Northern Hemisphere they begin as north-northeast winds at about latitude 30°N in January and latitude 35°N in July, gradually veering to northeast and east-northeast as they approach the equator. Their southern limit is a few degrees north of the equator. The southeast trades occupy a comparable region in the Southern Hemisphere and similarly change from south-southeast on their poleward side to southeast near the equator. In the Pacific, the trade winds are properly developed only in the eastern half of that ocean, and in the Indian Ocean, only south of about 10°S. They are primarily surface winds, their usual depth being from 3000 to 5000 ft, although they sometimes extend to much greater altitudes. They are characterized by great constancy of direction and, to a lesser degree, speed; the trades are the most consistent wind system on earth.
    See antitrades, tropical easterlies, equatorial easterlies.

  2. A name given to the prevailing westerlies in California and to the northwest winds that blow in Oregon in summer.