What Causes Wind?

Wind is an air current,moving with speed in any direction.As well as currents of air that flow across the earth's surface,there are upward and downward currents of air.A variety of conditions give rise to these winds,particularly land and sea breezes,which affect the coastal and lake side areas.These breezes are the result of the different rates at which land and water bodies heat up and cool down.This produces local pressure changes,and thus deermine the direction of these winds.Wind has an important effect on air temperature .This is known as the chill factor, which causes the wind to make  the air feel colder.

The amount of heat absorbed by the earth's surface varies from place to place.In high latitudes the sun rays have to pass through a greater thickness of atmosphere and they also spread  out  over a larger area.It is the equator where the  sun rays are most concentrated .Here the heated  air expands  and rises,creating  a low pressure area into which trade winds blow from north and south.The doldrums is the name given to the area of low pressure  around the equator.It is marked by calms:sailing ships tried to avoid the doldrums because they might be stationary for days at a time.
            As it rises  and spread north and south,the warm air from the equator cools.Around latitudes 30 degrees north and 30 degrees south (the Horse Latitudes),it finally sinks back to form an area of high pressure.From the Horse Latitudes some of the air flows back to the equator,and some flows  towards the poles as  winds known as the westerlies.These  relatively warm westerlies  finally meet cold,dense air  flowing from the north and souh poles .In these ways the winds redistribute heat around the earth's surface. As the map of the world's major wind belts shows,the air currents do not flow in  a north-to-south direction.Instead ,they are deflected  by the Coriolis Force,caused by the earth's rotation on its axis  from west to east.This has the effect that winds  and ocean currents in the northern Hemisphere are deflected to the right of the direction in which they are moving.The opposite occurs in the southern hemisphere.The Coriolis Force ,therefore ,is responsible for the north-east and southe-east trade winds,the north-westerlies and south-westerlies and the polar easterlies.