3. Pressure Gradient Force How does the air move as a result of the pressure gradient force? 996hPa 998hPa 1000hPa 1002hPa LOW PRESSURE HIGH PRESSURE (1) Right angle to isobars (2) From high pressure to low pressure

4. 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

6. 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

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

8. 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.

10. Ekman Spiral

11. Cyclone in NH Cyclone in SH

12. 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? Unresolved Questions