Trade wind

The trade winds (also called trades) are the prevailing pattern of easterly winds found in the tropics near the Earth's equator [cite web|author= |title= trade winds|work=Glossary of Meteorology |publisher= American Meteorological Society |date= 2000 |accessdate=2008-09-08|url=http://amsglossary.allenpress.com/glossary/search?id=trade-winds1 |quote= ] . The trade winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere. The trade winds act as the steering flow for tropical storms that form over the Atlantic, Pacific, and Indian Oceans that make landfall in North America, Southeast Asia, and India, respectively.

Origin of the name

Their name originally derives from the late Middle English word 'trade' (borrowed from Middle Low German, and cognate with English 'tread'), meaning "path" or "track," and thence the obsolete nautical phrase "the wind blows trade," that is to say, on a consistent track. However, by the 18th century, because of the importance of these winds to England's merchant fleet crossing the Atlantic Ocean, both etymologists and the general public had come to identify them with a later meaning of 'trade', "(foreign) commerce". ["Trade-Wind", "Oxford English Dictionary", Second Edition, p.225.]

Origin of the winds

The surface air flows toward the equator and the flow aloft is poleward. A low-pressure area of calm, light variable winds near the equator is known to mariners as the doldrums. Around 30° N. and S., the poleward flowing air begins to descend toward the surface in subtropical high-pressure belts. The sinking air is relatively dry because its moisture has already been released near the Equator above the tropical rain forests. Near the center of this high-pressure zone of descending air, called the "Horse Latitudes," the winds at the surface are weak and variable. The term Horse Latitudes probably came from the "dead horse" ritual, a practice in which the seamen would parade a straw-stuffed effigy of a horse around the deck before throwing it overboard.

The surface air that flows from these subtropical high-pressure belts toward the Equator is deflected toward the west in both hemispheres by the Coriolis effect. Because winds are named for the direction from which the wind is blowing, these winds are called the northeast trade winds in the Northern Hemisphere and the southeast trade winds in the Southern Hemisphere. The trade winds meet at the doldrums. Surface winds known as "westerlies" flow from the Horse Latitudes toward the poles. The "westerlies" meet "easterlies" from the polar highs at about 50-60° N. and S.

Among the most well known trade winds is the alizé (sometimes alize), a steady, mild northeasterly wind which blows across central Africa and the Caribbean. It brings cool temperatures between November and February.

Trade winds are known to blow across Madagascar and other regions in the area.They are usually strongest in April to October but they do blow all year long.

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