Post on 16-Dec-2015
Pressure Gradient ForcePressure Gradient Force• How does the air move as a result of the
pressure gradient force?
996hPa
998hPa1000hPa
1002hPa
LOW PRESSURE
HIGH PRESSURE
(1) Right angle to isobars
(2) From high pressure to low pressure
Coriolis ForceCoriolis 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– Ferrel’s law
New Things to learn in F6New 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
Geostrophic Wind BalanceGeostrophic Wind Balance
996hPa
998hPa1000hPa
1002hPa
LOW PRESSURE
HIGH PRESSURE
Pressure gradient forceCoriolis force
Resulting wind
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.
Ekman SpiralEkman Spiral
Cyclone in NH
Cyclone in SH
Why do we have Wind blowing clockwise inward in the cyclone in NH?
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?
Unresolved QuestionsUnresolved Questions