1. Physical Science Lecture 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