We have a love-hate relationship with wind. It can provide a welcome breeze or destroy umbrellas, mess with our hair and even cause untold destruction. Worse still, there's nothing we can do about it. Wind is just ... there! But what causes it?
Wind is caused by differences in atmospheric pressure, which are themselves largely the result of unequal heating of the planet's surface by the sun. Air "wants" to move from a high-pressure to a low-pressure zone and, although any difference in pressure can cause wind, greater differences produce stronger winds. Air directly above an area experiencing intense heating expands and moves away. This creates a low-pressure area that cooler, heavier air then rushes in to fill. If the Earth did not rotate, wind would move directly from high-pressure to low-pressure areas. However, this path is deflected by the Earth's rotation to the left in the Southern Hemisphere and to the right north of the equator.
Now that we know what causes wind, it's interesting to note that there are broad air current zones, the so called "wind belts" that compose our planet's general air circulatory system. This system is divided into five zones, which can migrate with the sun and are known as primary wind belts:
- Doldrums -- the area that receives the most heat from the sun and is generally between 5 degrees north and south latitude
- Trade Winds -- the area extending past the doldrums to as far as 30 degrees north and south latitude
- Horse Latitudes -- a wind belt that forms at about 30 degrees north and south latitude between the trade winds and the prevailing westerlies
- Prevailing Westerlies -- these winds extend to about 60 degrees north and south latitude from the horse latitudes
- Polar Easterlies -- these winds reach to the poles from about 60 degrees north and south latitude.
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