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Equatorial productivity

Equatorial productivity. 2˚N. EQ. Trade Winds. 2˚S. West. East. EQ. Equatorial Divergence. map view. Ekman Transport {to right in NH}. DIVERGENCE. UPWELLING. Ekman Transport {to left in SH}. Trade Winds. X. X. X. 2˚S. 2˚N. Ekman Trans. Ekman Trans. {to left in SH}.

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Equatorial productivity

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  1. Equatorial productivity

  2. 2˚N EQ Trade Winds 2˚S West East EQ Equatorial Divergence map view Ekman Transport {to right in NH} DIVERGENCE UPWELLING Ekman Transport {to left in SH}

  3. Trade Winds X X X 2˚S 2˚N Ekman Trans. Ekman Trans. {to left in SH} {to right in NH} EQ Equatorial Divergence cross-section Surface Layer Thins DIVERGENCE UPWELLING

  4. Upwell Warm Water in West Upwell Cold Water in East Thick Warm Surface Layer Warm Surface Layer Thin Warm Surface Layer Bottom of Ekman Layer Thermocline Cold Deep Ocean West East EQ Equatorial upwelling - E vs. W Easterly Trade Winds

  5. Let’s have a look inside… www.pmel.noaa.gov/tao/jsdisplay/

  6. But there is more to the story of The “normal” condition in the pacific. The condition just described is greatly Enhanced by what is know as a “positive Feedback”

  7. Cold Deep Ocean West East Air-Sea Feedbacks Trade Winds Enhanced more by stronger Pressure Gradient Trade Winds Enhanced by Pressure Gradient Easterly Trade Winds Stronger H L H colder Upwelling Due to Winds Upwelling Enhanced by Winds Upwelling Enhanced even more by Winds

  8. Mean annual SST

  9. West East Air-Sea Feedbacks Walker Cell Or Walker Circulation L H

  10. “Normal” conditions

  11. “Normal” conditions • Walker Circulation Strong • Trades blow E to W • Thermocline shallow in E • Upwelling of cold water in E • High primary productivity in E • Warm water piles up in W • E to W temperature gradient reinforces trade winds

  12. Welcome to Our Dynamic Ocean (OCN104) Instructor Petra Dekens

  13. Let’s have a look inside… www.pmel.noaa.gov/tao/jsdisplay/

  14. Cold Deep Ocean West East Air-Sea Feedbacks Trade Winds Enhanced more by stronger Pressure Gradient Trade Winds Enhanced by Pressure Gradient Easterly Trade Winds Stronger H L H colder Upwelling Due to Winds Upwelling Enhanced by Winds Upwelling Enhanced even more by Winds

  15. Mean annual SST

  16. West East Air-Sea Feedbacks Walker Cell Or Walker Circulation L H

  17. “Normal” conditions

  18. “Normal” conditions • Walker Circulation Strong • Trades blow E to W • Thermocline shallow in E • Upwelling of cold water in E • High primary productivity in E • Warm water piles up in W • E to W temperature gradient reinforces trade winds

  19. West East Air-Sea Feedbacks Walker Cell Or Walker Circulation L H

  20. What is an El Niño? Walker Circulation Gone, reverse flow West East

  21. www.pmel.noaa.gov/tao/elnino

  22. Annual Average “Normal” Short-lived deviation from “Normal”: El Niño (March 1998)

  23. El Niño conditions • Walker Circulation Weak or Gone • Trades very weak or reversed • Thermocline deep in E • Upwelling of warm water in E • Lower primary productivty in E compared to normal years • Sea level rises in E • E to W temperature gradient reduced or gone

  24. West East Equatorial cross-section (across the Pacific) Top of troposphere Walker Cell Or Walker Circulation Darwin, Australia L H Tahiti, Central Pacific

  25. Southern Oscillation Index • Darwin, Australia = Normally Low Pressure • Tahiti = Normally High Pressure • SOI is = Pressure at Tahiti minus Pressure at Darwin • Normal conditions: SOI is positive • El Nino conditions: SOI is negative

  26. West East Normal Rainfall Walker Cell Or Walker Circulation Lots of Rain L H Very Dry

  27. Walker Circulation Gone, reverse flow West East El Niño Rainfall Dry (fires in Australia) Wet (floods in Peru)

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