Harnessing the power of two special belts of winds
In the early days of exploration under sail, two large belts of winds were discovered blowing toward the equator: from the northeast north of the equator and from the southeast south of the equator. The word trade in those days meant to advance steadily and was synonymous with track and path. The trade winds did indeed allow those un-handy sailing vessels to advance steadily—and, of course, to set up patterns of international trade.Contrary to common belief, the trade winds are not totally steady in force or direction, but they do trend in the general direction of southwest and northwest at an average speed of force 4 on the Beaufort Scale, or 11 to 16 knots. Their actual speed at any one time varies with the seasons, and can reach force 7 (28 to 33 knots) at times, usually in winter. The trade-wind belts also move north and south as a whole with the sun, covering an area of many hundreds of miles between the approximate latitudes of 30 degrees north and south and the equator, where they are separated by an area of low pressure known as the doldrums.The trades are suppressed by the monsoons in some areas, mainly the Indian Ocean, the western portion of the Pacific, and West African waters. In summer, they can also turn into the
 |
| World wind patterns, January to March. |
 |
| World wind patterns, April to June |
 |
| World wind patterns, July to September |
 |
| World wind patterns, October to December |
tropical revolving storms known as hurricanes, cyclones, or typhoons. These storms usually occur in late summer.In the trade winds, the weather is generally fair and hot. Puffy white trade-wind clouds dot the sky from horizon to horizon, and it seldom rains except toward the western reaches of the trade-wind belts, where thunderstorms become more common as you approach the doldrums.Off the Portuguese coast, the so-called Portuguese trade wind blows from the north, reaching moderate gale force in summer. Clipper-ship sailors also sometimes referred to the Roaring Forties as trade winds.Most small sailboats take advantage of the trades when crossing oceans, and many fly special downwind sails that avoid the chafe of the ordinary mainsail-foresail arrangement; they move the center of effort forward to ease the wind vane’s task of steering to leeward in light weather. Beating to windward against the trades requires a weatherly boat and a brave long-suffering crew.See also
Beaufort Scale; Doldrums; Horse Latitudes.
