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The westerlies, anti-trades, [2] or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes (about 30 degrees) and trend towards the poles and steer extratropical cyclones in this general manner. [ 3 ]
The westerlies play an important role in carrying the warm, equatorial waters and winds to the western coasts of continents, [13] [14] especially in the southern hemisphere because of its vast oceanic expanse. The westerlies explain why coastal Western North America tends to be wet, especially from Northern Washington to Alaska, during the winter.
The term originally derives from the early fourteenth century sense of trade (in late Middle English) still often meaning "path" or "track". [2] The Portuguese recognized the importance of the trade winds (then the volta do mar, meaning in Portuguese "turn of the sea" but also "return from the sea") in navigation in both the north and south Atlantic Ocean as early as the 15th century. [3]
The westerlies can be particularly strong, especially in the southern hemisphere, where there is less land in the middle latitudes to cause the flow pattern to amplify, which slows the winds down. The strongest westerly winds in the middle latitudes are within a band known as the Roaring Forties , between 40 and 50 degrees latitude south of the ...
The weaker Westerlies of the Ferrel cell, however, can be disrupted. The local passage of a cold front may change that in a matter of minutes, and frequently does. As a result, at the surface, winds can vary abruptly in direction. But the winds above the surface, where they are less disrupted by terrain, are essentially westerly.
The largest ocean gyres are wind-driven, meaning that their locations and dynamics are controlled by the prevailing global wind patterns: easterlies at the tropics and westerlies at the midlatitudes. These wind patterns result in a wind stress curl that drives Ekman pumping in the subtropics (resulting in downwelling) and Ekman suction in ...
Roaring Forties as they contract towards southern Australia (observed in September 1895). [1]The Roaring Forties are strong westerly winds that occur in the Southern Hemisphere, generally between the latitudes of 40° and 50° south. [2]
A third explanation, which simultaneously explains both the northern and southern horse latitudes and does not depend on the length of the voyage or the port of departure, is based on maritime terminology: a ship was said to be 'horsed' when, although there was insufficient wind for sail, the vessel could make good progress by latching on to a ...