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Mean annual SST

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

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Mean annual SST

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  1. Mean annual SST

  2. West East EQ Equatorial Divergence

  3. 2˚N EQ Trade Winds 2˚S West East Equatorial Divergence map view Ekman Transport {to right in NH} DIVERGENCE Ekman Transport {to left in SH}

  4. Trade Winds X X X 2˚S 2˚N Ekman Trans. Ekman Trans. {to left in SH} {to right in NH} Equatorial Divergence cross-section

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

  6. Warm Surface Layer Cold Deep Ocean West East Equatorial upwelling - E vs. W Easterly Trade Winds

  7. Thick Warm Surface Layer Warm Surface Layer Thin Warm Surface Layer Thermocline Cold Deep Ocean West East Equatorial upwelling - E vs. W Easterly Trade Winds

  8. 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 Equatorial upwelling - E vs. W Easterly Trade Winds

  9. Cold Deep Ocean West East Air-Sea Feedbacks Easterly Trade Winds L H Upwelling Due to Winds

  10. Cold Deep Ocean West East Air-Sea Feedbacks Trade Winds Enhanced by Pressure Gradient Easterly Trade Winds L H colder Upwelling Due to Winds Upwelling Enhanced by Winds

  11. 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 colder Upwelling Due to Winds Upwelling Enhanced by Winds Upwelling Enhanced even more by Winds

  12. Mean annual SST

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

  14. Cold sinking air Warm rising air A big result of Different “Pressure” zones: moisture. WIND As air rises, it cools, water condenses, lots of rain As air sinks, it warms, lots of evaporation WIND LOW Pressure HIGH Pressure W E

  15. “Normal” conditions

  16. “Normal” conditions • Walker Circulation Strong • Trades blow E to W • Thermocline shallow in E • Upwelling of cold water in E • Warm water piles up in W • E to W temperature gradient reinforces trades

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

  18. El Niño conditions

  19. El Niño conditions • Walker Circulation Weak or Gone • Trades very weak or reversed • Thermocline deep in E • Upwelling of warm water in E • Sea level rises in E • E to W temperature gradient reduced or gone

  20. “Normal” “El Niño” www.pmel.noaa.gov/tao/elnino

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

  22. La Niña conditions • Walker Circulation Stronger than normal

  23. Normal conditions El Niño conditions

  24. West East Normal rainfall Walker Cell Or Walker Circulation Lots of Rain L H Very Dry

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

  26. La Niña anomaly map

  27. El Niño anomaly map

  28. El Niño impacts - precipitation patterns

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