Forces Affecting Wind

1
Forces Affecting Winds
2
Pressure Gradient Force

• How does the air move as a result of the pressure
  gradient force?

(1) Right angle to isobars
LOW PRESSURE
996hPa
998hPa
1000hPa
1002hPa
HIGH PRESSURE
(2) From high pressure to low pressure
3
Coriolis Force

• What you have learnt in F4?
• Due to earth rotation
• The air moves to right in NH
• The air moves to left in SH
• Ferrels law

4
(No Transcript)
5
New Things to learn in F6

• Factors Affecting Coriolis Force
• - Cf -2WVsin A
• where W is the angular velocity of the rotation
  of the earth
• (15?/hour 0.0000729rad/hour)
• V is the velocity of the air mass
• A is the latitude
• Cf is the Coriolis force

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Geostrophic Wind Balance
LOW PRESSURE
996hPa
998hPa
1000hPa
1002hPa
HIGH PRESSURE
Pressure gradient force
Resulting wind
Coriolis force
7
Necessary Conditions

• . Geostrophic wind takes place above the
  influence of surface frictional drag, air
  movement is controlled by the horizontal pressure
  gradient force and the Coriolis force.
• For the purpose of explaining horizontal air
  movement, or wind, the forces of gravity and the
  vertical pressure gradient may be assumed to
  cancel each other out.

8
Upper Level Condition -gt No friction
9
Ekman Spiral
10
Cyclone in NH
Cyclone in SH
11
Why do we have Wind blowing clockwise inward in
the cyclone in NH?
Unresolved Questions
Why do we have Wind blowing anti-clockwise inward
in the cyclone in SH?
Why do we have Wind blowing clockwise inward in
the cyclone in NH?
Why do we have Wind blowing clockwise inward in
the cyclone in NH?