Understanding Global Air and Ocean Circulation Systems

1. Physical ScienceLecture 154 Instructor: John H. Hamilton

2. Last lecture review • Driving forces of air motion • Temperature induced pressure gradients • Wind generation • Convective currents • Coriolis affect

3. Recommended exercises solutions • Teach somebody how the coriolis affect works • Teach someone, using the 2 air columns and assumptions, how wind is produced

4. Lecture review • Global circulation patterns • Major cells • Hadley • Ferrel • Polar • Upper atmospheric circulation • Ocean circulation • Surface currents • Deep water currents

5. Diagram first!

6. Hadley cells • Hadley cells are direct. They are convective currents created by solar heating • The Hadley cell starts on the equator where warm moist air rises straight up and then moves towards the poles. • The air sinks at about 30 degrees latitude (horse latitudes) and is warmed by compression as it sinks (here are the worlds great deserts)

7. Polar cells • Polar cells, like Hadley cells are directly driven by solar heating • Solar heating at about 60 degrees latitude warms air that rises, moves towards the poles and sinks

8. Ferrel cells • Ferrel cells are not directly driven by heating, rather they are indirectly driven by motion of the other cells.

9. Major winds • Trade winds • Westerlies • Polar easterlies (easterlies)

10. Major winds diagram

11. Upper atmosphere circulation • In the upper troposphere, at about 9-14 km rivers of air called jet streams move along at 95-190 km/hr • Each hemisphere has 2 major jet streams, a polar jet stream and a subtropical jet stream

12. Jet streams, driving force • At about 60 degrees latitude is the polar front, where cold air from the polar regions encounters warm moist air from the tropics, this temperature gradient causes a pressure gradient that drives the polar jet stream • At about 30 degrees latitude warm air moving towards the poles encounters the tropical front which also creates a temperature gradient.

13. Ocean surface currents • Surface ocean currents are driven and directed by a combination of the prevailing winds and coriolis forces. Called the Ekman transport

14. Mounding and depressions • With the prevailing winds being the direction that they are, the Ekman transport is such a that water mounds up at 30 degrees latitude and is depressed at the equator.

15. Gyres • Water wants to run “downhill” combining the rises and depressions with the Coriolis affects we get a circular flow of water around the elevated water called a “gyre” all major oceans have a gyre

16. diagram

17. Major ocean currents • Most of the major surface currents are parts of the water flowing arround a gyre • Example gulf stream

18. Deep water currents • Deep water currents are slower than surface currents and are driven by water in th polar regions increasing in salinity because of water freezing out. • Water freezes at the poles. Since water is leaving and becoming ice, the remaining water has a greater salinity and therefore a greater density and sinks

19. diagram

20. Lecture Review • Global circulation patterns • Major cells • Hadley • Ferrel • Polar • Upper atmospheric circulation • Ocean circulation • Surface currents • Deep water currents

21. Recommended exercises • Teach someone about the 3 major circulatory cells and how they are formed • Starting with wind and the coriolis affect explain to someone how gyrs are formed and what affect those gyrs have on local climate