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The Word on the Weather
http://www.gympieweather.com |
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Wind Flow |
As we look at satellite pictures it is
easy to distinguish the continuous circular movement of cloud masses.
This circular movement of weather patterns is caused by the rotation of
our planet. At the equator the earth spins at 1,670 kph, at the poles
however, the earth has no rotational speed at all. The best way to
explain this phenomenon is to consider a merry-go-round. If you were to
throw a ball from somewhere near the centre of the merry-go-round an
observer would see the ball appear to follow a curved path, on earth the
moving air displays a similar deflection. Since the globe is rotating,
any movement in the Southern hemisphere is diverted to the left, if we
look at it from our own position on the ground. (In the Northern
hemisphere it is diverted to the right). This apparent bending force is
known as the Coriolis force. (Named after the French mathematician
Gustave Gaspard Coriolis 1792-1843). The Coriolis force is a visible
phenomenon. Railroad tracks wear out faster on one side than the other.
Riverbeds are dug deeper on one side than the other. (Which side depends
on which hemisphere we are in: In the Southern hemisphere moving
particles are bent towards the left). In the Southern hemisphere the
wind tends to rotate clockwise (as seen from above) as it approaches a
low-pressure area. In the Northern hemisphere the wind rotates counter
clockwise around low-pressure areas. The wind rises from the equator and
moves north and south in the higher layers of the atmosphere. Around 30°
latitude in both hemispheres the Coriolis force prevents the air from
moving much further, at this latitude there is a high pressure area as
the air begins sinking down again. As the wind rises from the equator
there will be a low pressure area close to ground level attracting winds
from the North and South. At the Poles, there will be high pressure due
to the cooling of air. Keeping in mind the bending force of the Coriolis
force, we thus have the following general results for the prevailing
wind direction: |