The trade winds are part of the earth's atmospheric circulation

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".^[2]

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 name for this area is believed to have been given by colonial sailors, who, becalmed sometimes at these latitudes while crossing the oceans with horses as cargo, were forced to throw some overboard to conserve water.

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.

References

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