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Ocean Gyres - combine knowledge of global winds and Ekman flow - surface transport can be determined from wind direction/velocity - surface transport alters.

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Presentation on theme: "Ocean Gyres - combine knowledge of global winds and Ekman flow - surface transport can be determined from wind direction/velocity - surface transport alters."— Presentation transcript:

1 Ocean Gyres - combine knowledge of global winds and Ekman flow - surface transport can be determined from wind direction/velocity - surface transport alters ocean surface dynamic height - dynamic height differences => geostrophic flow in ocean Geography 104 - “Physical Geography of the World’s Oceans”

2 Ekman transport is 90° to right (NH) of the wind

3 global atmospheric circulation tropical

4 Global Atmospheric Pressure and Winds July January

5 cyclonic & anti-cyclonic wind effects L H

6 Ekman transport convergence, downwelling Ekman transport divergence, upwelling generally cooler water from upwelling generally warmer surface waters

7 cyclonic & anti-cyclonic wind effects Ekman transport convergence, downwelling Ekman transport divergence, upwelling

8

9 Global Winds and Atmospheric Pressure July January Trade Winds Westerlies

10 = High Pressure Geostrophic Currents

11 Ekman transport alters sea level (dynamic topography)

12 Sloped sea surface => pressure gradient Geostrophic Flow in Ocean – Pressure and Coriolis force balance

13 Subtropical Gyre Circulation from Figure in Text

14 Southern Hemisphere Subtropical Gyre going wrong direction!!!!

15 geostrophic subtropical gyres

16 major ocean gyres and currents

17 global chlorophyll & primary productivity - Aug. 2004 lowest chlorophyll concentration in center of sub-tropical gyres

18 measuring dynamic height by satellite deviation due to ocean currents geoid

19 global dynamic height – satellite measurements

20 global dynamic height

21 Global Surface Currents from Altimetry

22 http://argo.colorado.edu/~realtime/gifs_tmp/global_ssh/gmt.13083.gif dynamic height in the Gulf of Mexico

23 Mapped SSH in California Current geostrophic flow direction is along lines of constant SSH

24 CTD deployment for dynamic height measurement

25 global dynamic height – shipboard measurements units: meters 5.3 4.1 5.6 5.0 6.3 5.6 4.4 5.5 Differences in dynamic height are important, not absolute values

26 Ocean Currents Associated with Dynamic Height Contours

27 major ocean gyres and currents

28 trash in the North Pacific subtropical gyre Curtis C. Ebbesmeyer ~ 6 years to orbit N Pacific subtropical gyre

29 Summary - cyclonic winds => surface divergence, upwelling - anticyclonic winds => surface convergence, downwelling - direct wind driven Ekman transport sets up sea level variations - sea level variations (dynamic height) => geostrophic circulation - for geostrophic flow currents are along lines of constant sea level (dynamic height) - subtropical gyres are primary characteristic of ocean circulation

30 Readings (Surface and Deep Circulation): Text Chapter 9 (pgs 170 – 172) Reader pgs. 131 - 132


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