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GEOSTROPHIC (WIND-DRIVEN) CIRCULATION

S. GEOSTROPHIC (WIND-DRIVEN) CIRCULATION. Surface winds Ekman Spiral Eastern and Western Boundary Currents Upwelling Surface Currents Gyre Formation Sea Surface Topography Mass Transport Gulf Stream Rings Gulf of Mexico Rings. P. Ocean currents and climate. ZONAL ISOTHERMS.

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GEOSTROPHIC (WIND-DRIVEN) CIRCULATION

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  1. S GEOSTROPHIC (WIND-DRIVEN) CIRCULATION Surface winds Ekman Spiral Eastern and Western Boundary Currents Upwelling Surface Currents Gyre Formation Sea Surface Topography Mass Transport Gulf Stream Rings Gulf of Mexico Rings

  2. P Ocean currents and climate ZONAL ISOTHERMS Fig. 7-8a

  3. S SURFACE WINDS

  4. P Basically zonal

  5. S Measuring surface currents Fig. 7.2

  6. S EKMAN SPIRAL

  7. P Ekman spiral • Surface currents move at angle to wind • Ekman spiral describes speed and direction of seawater flow at different depths • Each successive layer moves increasingly to right (N hemisphere) Fig. 7.5

  8. P Ekman transport • Average movement of seawater under influence of wind • 90o to right of wind in Northern hemisphere • 90o to left of wind in Southern hemisphere Fig. 7.6

  9. S SURFACE CURRENTS

  10. P orange arrows = wind yellow arrows = water

  11. P Ocean gyres • Subtropical gyres • Centered about 30o N or S • Equatorial current • Western Boundary currents • Northern or Southern Boundary currents • Eastern Boundary currents Fig. 7.3

  12. P Other surface currents • Equatorial Countercurrents • Subpolar gyres Fig. 7.4

  13. S Zonal Currents (E-W)Boundary Currents (~N-S)

  14. S BOUNDARY CURRENTS

  15. PP > 2 knots < 2 knots

  16. P Atlantic Ocean circulation • North Atlantic Subtropical Gyre • North Equatorial Current • Gulf Stream • North Atlantic Current • Canary Current • South Equatorial Current • Atlantic Equatorial Counter Current

  17. P Atlantic Ocean circulation • South Atlantic Subtropical Gyre • Brazil Current • Antarctic Circumpolar Current • Benguela Current • South Equatorial Current Fig. 7.14

  18. P

  19. S UPWELLING

  20. S

  21. 07_12a-c S

  22. P Coastal upwelling • Ekman transport moves surface seawater offshore (upwelling) Fig. 7.11a

  23. P Other surface currents • Equatorial Countercurrents • Subpolar gyres Fig. 7.4

  24. P Low concentrations except in equatorial Pacific and high latitudes at the surface

  25. S 502 10/22 GULF STREAM RINGS

  26. S

  27. P Rings, or eddies, are important because they transfer heat, salt, plants and animals across strong boundaries.

  28. P Gulf Stream • Best studied • Meanders or loops • Warm-core rings • Cold-core rings • Unique biological populations Fig. 7.16

  29. S Cold-core Rings

  30. S

  31. S GULF OF MEXICO RINGS

  32. P

  33. S

  34. http://www.youtube.com/watch?v=JMLy4jV7Xgo

  35. S 504 10/24 GYRE FORMATION

  36. PP North Atlantic Gyre South Atlantic Gyre

  37. P Geostrophic flow • Ekman transport piles up water within subtropical gyres • Surface water flows downhill (gravity) and • Also to the right (Coriolis effect) • Balance of downhill and to the right causes geostrophic flow around the “hill” Fig. 7.7

  38. P Western intensification • Top of hill of water displaced toward west due to Earth’s rotation • Western boundary currents intensified • Faster • Narrower • Deeper

  39. P

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