1. Ocean Surface Circulation
Motion in the Ocean, Part I, or Why does the ocean have currents, and why do they move in circles?

2. Two types of Ocean Circulation:
Surface Circulation -- Wind-driven
Deep Circulation -- Density (T,S) driven

3. Atmospheric Circulation

4. Temperature and Pressure
As the Earth’s surface is heated, air is warmed, expands and rises (Low P)
Warm air carries water vapor
In the upper atmosphere the air cools and sinks (High P)
This round-trip is called a “cell”

5. Things get interesting!
On a rotating planet, moving objects appear to be deflected
Why is this?

6. Coriolis Deflection (aka “I Could Care Less” force)
Apparent force due to Earth’s rotation
Deflection in path of motion when viewed from a rotating reference frame
Gustave-Gaspard Coriolis (1835)
Familiar from merry-go-rounds
Significant only for large distances (not toilets and billiards!)

7. Coriolis “movie”

8. Coriolis Deflection

9. Consequences of Coriolis
Moving fluids (atmosphere and ocean) turn to the right in the Northern Hemisphere
Moving fluids (atmosphere and ocean) turn to the left in the Southern Hemisphere

10. Global Wind Circulation

11. Wind-Driven Ocean Circulation
Steady winds produce waves and set the surface water in motion
Moving water is deflected to the right (N.Hemisphere) or left (S.Hemisphere)
This starts the main “gyre” motion of the surface ocean

12. Surface Ocean Circulation

13. Main Features Five large gyres Antarctic Circumpolar Current
Equatorial Countercurrent
Velocities vary -- fastest are meters/sec

14. 106 m3/sec (Sverdrup) = all the rivers

15. Gulf Stream - Benj Franklin

16. Gulf Stream

17. So, do the gyres just follow the winds?
Not exactly! But the winds get the motion in the ocean started
The oceans respond by flowing and turning
Water piles up in the center of gyres -- several meters high

18. Ekman Transport -- moves water 90° to the winds

19. Upwelling and Oregon’s Ocean
Winter winds from the south -- downwelling
Summer winds from the north -- upwelling

20. Winter Summer

21. Global Wind Circulation

22. Geostrophic Currents

23. Coriolis deflection plus the Pressure Gradient steers the currents around the gyres

24. Northern Hemisphere Gyres

25. Surface Circulation

26. How do we track ocean circulation?
Fixed Buoys -- measure current speed and direction
Drifters -- travel with the currents and transmit their location

27. Beach Swap Meets!

28. Tracking Currents: The Story of the Lost Nikes
1: 60,000 shoes spilled, May 1990
2-8: 1990-’91
9: 1993
10: 1994