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.
References
Weather, Wikipedia, http://en.wikipedia.org/wiki/Weather
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