Hydrostatic balance 1 Atmospheric pressure P Force F

Hydrostatic balance 1. Atmospheric pressure P: Force F acting on unit area due to the weight of the atmosphere. Why things do not fly away from surface? 2. Hydrostatic balance: The upward pressure gradient force balances the downward gravity. Pressure gradient force Gravitational force

3. What controls the horizontal pressure distribution? It’s temperature! 4. Force and winds Horizontal pressure gradient force

Sea breeze

Winds at high altitudes do not blow from high pressure to low pressure, rather, they blow along the constant pressure called isobars. Why?

5. Coriolis effect

Coriolis Deflection Depends on Latitude Z Z r North Pole to a u Eq

6. Geostrophic Balance Low pressure Pressure gradient force Geostrophic Wind Coriolis force High pressure

7. Curved flow and Gradient Wind L H Anti-clockwise (cyclonic) Clockwise (anti-cyclonic)

8. Effect of frictional force

L H

9. Vertical structure of pressure system

10. Vertical variation of geostrophic wind --- thermal wind

What causes wind variation with height? P’-1 P P’ Z 2 P+1 Thermal wind: wind difference between two levels Z 1

Thermal wind Z Fp 2 ΔP 1=P 11 -P 12=20 h. Pa B low Vg 2 Fc 2 Cold high low A Warm high

Mid-latitude westerly and jet stream