Transcript Forces Affecting Wind

Pressure Gradient Force
• How does the air move as a result of the
pressure gradient force?
LOW PRESSURE
(1) Right angle
to isobars
996hPa
998hPa
1000hPa
1002hPa
HIGH PRESSURE
(2) From high pressure to low pressure
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
Ferrel’s law
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
Geostrophic Wind Balance
LOW PRESSURE
996hPa
998hPa
1000hPa
1002hPa
HIGH PRESSURE
Pressure gradient force
Coriolis 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 Spiral
Cyclone in NH
Cyclone in SH
Unresolved Questions
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?