Global wind patterns

Global wind patterns: Winds are named by the direction from which they blow. The globe is encircled by six major wind belts, three in each hemisphere. From pole to equator, they are the polar easterlies, the westerlies, and the trade winds. All six belts move north in the northern summer and south in the northern winter. Each belt occupies about 30 degrees of latitude, that is, one third of the way from the pole to the equator.

Polar Easterlies: At about the latitude of Norway, Alaska U.S.A, and northward (60-90 degrees), the Polar easterlies blow irregularly from the east and north.

Polar Front: Between the polar easterlies and the westerlies is the polar front.

Prevailing Westerlies: At about the latitude of Western Europe and Continental U.S. (30-60 degrees), the Westerlies blow from the west, tending somewhat toward the north. This causes most weather in the United States to move from west to east.

Horse Latitudes: Where the Westerlies meet the trade winds at about 30 degrees (Jacksonville, Florida) is the Horse latitudes, also Variables of Cancer, Subtropical High, or Subtropical ridge. This is a region of high pressure, dry air, and variable winds, and is associated with deserts over land.

Trade Winds: South of about 30 degrees the northern or northeast trade winds blow mostly from the northeast toward the equator. These were the sailor's favorite winds, since the weather was warm, and the winds usually blew steadily in an advantageous direction. Columbus used these to sail to the Caribbean.

Doldrums: At about the equator is Intertropical Convergence Zone or doldrums, a region of light and irregular wind broken by occasional thunderstorms and squalls. The width and exact location of the doldrums were hard to predict. Sailing ships are sometimes becalmed here for many days waiting for a proper wind.

Southern hemisphere: In the southern hemisphere the belts are reversed. The southeast trade winds blow from the southeast toward the equator. The southern equivalent of the horse latitudes (or Variables of Cancer) is called the Variables of Capricorn. The southern westerlies start somewhat south of South Africa. They tend to be stronger than the northern westerlies because they are mostly over water (roaring forties). The southern polar easterlies are mostly over Antarctica.

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Wikipedia