ARTICLE INDEX:
1. Gravitational Force
This is related to the mass of the air and is directed downwards perpendicular to the earths surface. This is usually counter balanced largely by the upwards pressure gradient forces.
2. Pressure Gradient Force
The pressure gradient force is the change in pressure over a distance. This is manifested mostly in a horizontal direction, but there is also a vertical component, which was referred to in 1 above as counterbalancing the gravitational force on air. The differences in pressure can usually be traced back to uneven heating of the earth surface by the sun. The force can be derived from the following equation:
PG Force = |
___1____ |
x |
Change in Pressure |
| |
Air Density |
|
Distance |
3. Coriolis Force
This is due to the fact that the surface of the earth is traveling at different speeds as one moves from the equator to the poles. This is an apparent force. It is only becomes into play if the air is moving.
Coriolis Force = +/- f V
where v is the velocity of the wind,
and f = 2X Earth's rate of rotation X the sine of the latitude.
This effect does not play a role at the small scale level.
4. Centrifugal Force
When wind moves in a circular path, eg in an anticyclone or cylone it experiences a force directed outwards from the centre of rotation. This effect does not play a role at the small scale level.
Centrifugal Force = V 2 / R
where V is the wind velocity
and
R is the radius of the curved path.
5. Friction Force
This is caused by wind flowing over the rough surface of the earth. (7)
Friction Force = - kV
where V is the wind velocity
and
K is a constant.
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