Definition of Wind Currents
Although wind currents are circular patterns of moving area, they really start at the equator with the help of the sun. However, important factors such as low- and high-pressure zones as well as the tilt of the earth also affect how wind blows. The most common global winds are tropical easterlies, prevailing westerlies and polar easterlies. But wind belts exist on smaller scales, too, such as North America's Chinook and the Mistral in France.
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Purpose
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Because the equator receives a majority of sunlight, air is constantly heated, which causes it to rise. This leaves low-pressure zones along the surface while the air moves in the opposite direction of the equator. At about 30 degrees latitude, the air cools and sinks and returns toward the equator at low altitude. However, not all of the sinking wind moves toward the equator. Some of it continues toward the poles between 30 degrees and 60 degrees, where it is joins the winds from the poles.
Factors
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Because air rises along the equator creating low pressure zones, eventually when the air cools off, it becomes heavier and moves back to the low-pressure areas. Wind generally blows from high pressure to low pressure. This is the reason sea breezes blow from high pressure, or cool areas on the ocean, to low pressure or hot areas inland on a warm summer day.
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Coriolis Effect
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Wind does not blow in straight lines north and south of the equator. Because the earth rotates at a tilt, wind currents are bent, creating what is called the Coriolis Effect. Wind currents between the latitudes of 30 and 60 degrees both north and south of the equator blow from the west and are called westerlies. Wind currents between the equator and latitude of 30 degrees to the north and south blow from the east and are called easterlies. However, at the poles, because wind sinks to the surface and is turned to the west by the Coriolis Effect, they are called polar easterlies, because they originated from the east.
Trade Winds
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Winds were especially important to sailors who relied on wind power to travel from place to place. The easterlies or tropical easterlies also are known as trade winds, because ships used these winds to trade. On the other hand, the Doldrums were areas of low pressure along the equator where the trade winds met and rose as heated air. Sailors avoided these areas because there was little to no wind flow.
Specific Winds
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There are also specific wind currents that affect local areas all around the planet. The warm winter wind called the Chinook in North America can bring both damage and relief to people, plants and animals. In France, the Mistral is a cold northwest blowing wind that moves down the Rhone Valley. In West Africa, the Harmattan blows dry air and dust storms across the Sahara.
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References
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- Photo Credit wind image by hanna kreis from Fotolia.com
