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Objectives

Objectives. learn how El Niño works emphasize that the ocean & atmosphere are strongly coupled understand that one component of the Earth’s system can have drastic effects on the rest of the Earth. El Niño: The Enigma. Unusual oceanic and atmospheric phenomenon - an anomaly

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Objectives

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  1. Objectives • learn how El Niño works • emphasize that the ocean & atmosphere are strongly coupled • understand that one component of the Earth’s system can have drastic effects on the rest of the Earth

  2. El Niño: The Enigma • Unusual oceanic and atmospheric phenomenon - an anomaly • We don’t know everything about it • We can’t really predict it yet

  3. El Niño: The Term • First discovered in 1795 • Recognized by local fisherman along Ecuador and Peru • Warm, surface countercurrent • North-->South • Discovered around Christmas-time • “The Christ Child”

  4. El Niño Characteristics • Normally develops in W. tropical Pacific • Often results in natural disasters • Occurs every 2 to 10 years • Most recent and severe events in 1953, ‘57-’58, ‘65, ‘72-’73, ‘76-’77, ‘82-’83, ‘91-’92, ‘97-’98, ‘02-’03

  5. Slides from 1982-’83 El Niño

  6. Suppressed Sea Surface Elevated Sea Surface

  7. “Southern Oscillation” (SO) • Tradewinds weaken or fail • Tropical winds reverse and go east instead of west • Atmospheric pressure cells reverse • Wet areas become dry (drought) • Dry areas get flooded • “oscillates” like a giant sea-saw, taking 3-5 months

  8. Non El Niño El Niño

  9. Coupled Ocean-Atmosphere Circulation Non El Niño El Niño

  10. Ocean’s Response to the SO • Warm water moves to the east • Elevates sea surface temperatures (SSTs) in SE Pacific • Shuts down upwelling, can induce downwelling • Reduces available nutrients • Kills fish and sea birds - especially bad off Peru

  11. Non El Niño El Niño

  12. Non El Niño El Niño Sea slope flattens westerly currents weaken Thermocline flattens Upwelling decreases

  13. Ocean AND Atmosphere • El Niño is both an oceanic and an atmospheric phenomenon • Often called ENSO • Scientists knew of SO from wind and precip. data • Scientists new of El Niño from SST data • Didn’t make connection until 1969

  14. Jacob Bjerknes • Jacob Bjerknes, a Norwegian meteorologist made breakthrough in 1969 • Combined wind, rain, AND SST data • Ocean & atm. part of “big climate engine” • Effects of ENSO not just local to Peru but could affect whole Pacific, whole world

  15. Interdisciplinarity Rules! • Bjerknes was a meterologist who was willing to take a good, hard look at oceanographic data • Oceanography a versatile science

  16. How Do We Track El Niño Today? • in situ (on site) measurements • Satellite sea surface temperature • Computer models

  17. Tropical Ocn Global Atm Tropical Atm-Ocn

  18. La Niña • NOT tied to the Southern Oscillation • Tradewinds get stronger • SSTs are lowered in SE Pacific • Normal conditions are exaggerated • Dry areas get drier (drought) • Wet areas get wetter (floods) • Occurs in between El Niños

  19. El Niño AND La Niña • Both an ocean/atmosphere phenomenon • Both affect wind, rain, and SST • Both occur in cycles

  20. Movies

  21. “Southern Oscillation” Tradewinds fail Reverse flow of air Elevated SST Upwelling decreased Fish die Dry areas flood Wet areas dry up No oscillation Tradewinds increase No reverse flow Decreased SST Upwelling increased Fish thrive Dry areas get drier Wet areas flood El Niño VERSUS La Niña

  22. Lesson to be Learned • Earth phenomena are very much interrelated Ocean <----> Atmosphere • Bjerknes’ concept of “teleconnections” • We must understand in order to predict • Invest in soybean futures after an El Niño! • No fish meal for cattle, farmers will use soy

  23. We’re dealing with the interplay between two very different fluids - atmosphere and ocean - in the boundless dimensions of time and space. ... Abnormality in one causes abnormality in the other.... Events such as El Niños have no definite starting point and no end. It’s a matter of where you break into the scene, and where you leave it. Perhaps the only thing more complex is human behavior itself. -- Dr. Jerome Namias, Scripps Institution of Oceanography

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