Sunday, June 17, 2012

What makes the wind blow?

The way the earth rotates sets the prevailing wind

Who knows why the Wind blows?  The Wind knows!

The wind started blowing ever since the earth gained an atmosphere over four and a half billion years ago, and it has been blowing ever since,  It is caused by many factors including the fact that the earth is rotating from west to east through space in its axis at around 1,000 MPH.  Most other causes for the wind to blow is caused by differences in the temperatures of various air masses and the amount of moisture they contain.  Another cause is caused by the proximity of high and low pressure system literally the closer their centers are to each other the harder the wind blows.

The primary reason why the prevailing wind goes from west to east is because the earth is rotating at a rate of about 1,000 MPH and the friction of the atmosphere dragging on the earth’s surface sets up a drag that not only causes the wind direction to be from west to east.  The same frictional drag causes eddies in the atmosphere that show themselves as high or low pressure systems.

A further consideration is the fact that hot air rises creating a low pressure area, eventually it gets so high in the atmosphere that it cools and loses its moisture.  At that point the heavier cold air starts to descend and becomes a high pressure system. 

This can be readily observed in a mountainous area where the westward winds carrying moisture and are comparatively warm are cooled from rising up and over the mountains and lose their moisture.  The dry air on the east side of the mountains now descends and is reheated by compression causing a rain shadow.

As it rises the warm moist air causes a low pressure system to form that causes air to be drawn into the system from an adjacent high pressure system.  The air being heavier and moisture depleted sends a stream of air out of the bottom of the system that is attracted to the adjacent low pressure system.  When it enters the low pressure system it has already been heated by compression where it picks up fresh moisture by evaporation off the earth’s surface.

The wind always blows from a high pressure system to a low pressure system because of the pressure differential between the two systems.  The closer together the systems the harder the wind blows. 

The prevailing westerly winds cause these two systems to spin like a top.  In the northern hemisphere a low pressure system spins counterclockwise and a high system spins clockwise.  In the southern hemisphere the order is reversed. 

Under the right circumstances it is possible for a high pressure system to be transformed to a low, and a low pressure system to become a high pressure system.  This depends on how much moisture they are able to attract or lose.


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