1. Global Circulation Geog. 1, Week 4, 19 March 2002 Chapter 6 of Christopherson Need to know Major Wind Patterns High and Low Pressure Systems

2. Start From Highly Simplified Model 1.Pressure differences 2.Equator/Pole air movement 3.Add in upper troposphere cooling 4.Add in rotation of Earth 5.Coriolis ‘Force’ 6.Effects of land mass

3. Basic Air Movement Caused by Pressure Differences Air moves from high pressure to low pressure region If air is heated, density drops and so pressure drops, e.g. sea breeze High 1025hPa Low 995hPa Average Pressure 1013hPa Air movement

4. High to Low Air Flow Causes Vertical Movement as Well CloudsWHY?Clear Low – air flow in at groundHigh – air flow out at ground Rising air above a low Falling air above a high

5. Equator to Pole Air Movement This model is too simple to be useful EquatorSouth Pole North Pole Heating

6. Equator to Pole Air Movement More realistic model Equator South Pole Heating Loses heat by radiation 30 o S60 o S L LH H Polar Front Hadley cell

7. 30 o N 30 o S From Christopherson, p. 149 Equator

8. Now Add In a Rotating Earth Apparent change in direction referred to as the Coriolis Effect Coriolis Force Northern Hemisphere -Clockwise round high -Anticlockwise round low Southern Hemisphere -Anticlockwise round high - Clockwise round low

9. Southern Hemisphere This clockwise/anticlockwise air movement around lows and highs defines the synoptic wind direction for Tasmania as these systems move past the State H L

10. Christopherson p.150

11. Hobart: cool, early drizzle, light to moderate southerly winds Friday 8 March 2002 (Mercury Newspaper)

12. C

13. northeasterly winds developing

14. Strong northerlies, very warm

15. Ocean Currents Similar general pattern except, obviously, restricted to the oceans Surface currents driven by prevailing winds Deep currents driven by changes in water density (e.g. cold Arctic water sinking and moving south through Atlantic ocean) Movement slower than air (1000 years for full cycle)

16. Christopherson p.162

17. Christopherson p. 164

18. Summary Large scale atmospheric movement of air due to uneven heating and cooling plus effect of Earth’s rotation and position of continents. This moves heat (energy) from equator towards poles. Ocean currents driven by wind and uneven heating/cooling of oceans. Slower than wind but large amounts of heat carried from equator towards poles.

19. Equator – movement of warm moist air into upper troposphere

20. Subtropical Highs – around 30 o S e.g. Byron Bay

21. Storms at polar convergence about 60 o S

22. Next Week The importance of evaporation and condensation of water in the atmosphere Chapter 7 of Christopherson