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Chap. 7 ENSO

Chap. 7 ENSO. sommaire général. 7.1 Oceanic climatology 7.2 Historical and theoretical development 7.3 Main Features of ENSO (ex. with El Ni ñ o 97) 7.4 Description of the Southern Oscillation 7.5 ENSO : regional climatic changes (Pacific and Africa) 7.6 Teleconnections

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Chap. 7 ENSO

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  1. Chap. 7 ENSO sommaire général 7.1 Oceanic climatology 7.2 Historical and theoretical development 7.3 Main Features of ENSO(ex. with El Niño 97) 7.4 Description of the Southern Oscillation 7.5 ENSO : regional climatic changes (Pacific and Africa) 7.6 Teleconnections 7.7 Seasonal forecasts ‣ To learn more about ENSO, see this web site http://www.educnet.education.fr/obter/appliped/elnino/theme/nino.htm

  2. 7.1 Oceanic climatology : SST Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Sea Surface Temperature

  3. 7.1 Oceanic climatology : SST Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Pourquoi des eaux plus Fraiches sur les cotes est des continents ?

  4. 7.1 Oceanic climatology: Ekman transport and coastal upwelling Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Northern Hemisphere : Ekman transport d’Ekman at right angle to the right of the wind stress In the southern hemisphere, It’s the opposite : Ekman Transport at right angle to the left of the wind stress

  5. 7.1 Climatologieocéanique : Transport d’Ekman et upwelling côtier Peru Chile Wind stress Ekman transport In the southern hemisphere, the Ekman transport is located at right angle to the left of the wind stress Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao

  6. 7.1 Oceanic climatology : 3D circulations in the Pacific Wind stress Coastal Upwelling Equatorial undercurrent Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao

  7. 7.1 Oceanic climatology : Sea-level Source : figure extraite du site du Jet Propulsion Laboratory (JPL). site : http://sealevel.jpl.nasa.gov Sea level more elevated over West Pacific

  8. 7.2 Historical and theoretical developments • Opposition of phase of the pressure between Sydney – Buenos Aires (Hildebrandsson – 1897) • Southern Oscillation (pressure, temperature, rain) – G. Walker (~1920) • Link between Pacific SST and Southern Oscillation (Bjerkness – 1966, 1969) – Apparition of the notion of Teleconnection • « Build-up » of Wyrtki (1975-1979) • Composite based on EL Niño events from the 1950s to 1970s– Rasmusson and Carpenter (1982) • Modelisation of the coupled ocean/atmosphere (1980 ….) • Theoretical developments(1980 …)

  9. 7.2 Historical and theoretical developements • « Build-up of Wyrtki • Ocean governed by the atmosphere (weakening of the trades – displacement of the warmpool in the direction of the East Pacific) • The delayed oscillator • Reflection of the Rossby wave into Kelvin wave (West coast) causing a deepening of thermocline. Reflection of the Kelvin waves (East coast). Alternation of warm anomalies (kelvin «downwelling») and cold (kelvin «upwelling»). • Couples instabilities • Link SST - thermocline (positive feed back with a convergent wind at surface) • Low-frequency unstable coupled mode (periode of 3 to 4 years and 6 months) • «SST mode» - advection of zonal mean gradient of SST by the anomalies of the current – advection of the mean vertical gradient of temperature by the anomalies of the vertical velocities – modulation of the vertical advection by the mean equatorial upwelling • Salt Barrier role : move of the east area of the Warmpool – role of the zonal advection of the SST gradient

  10. 7.3 Principales caractéristiques d’El Niño et illustration avec El Niño 97 • Ocean/Atmosphere Coupled phenomenon • ENSO : main source of variability of the climate at interannual timescales • Oceanic modifications « El Niño/La Niña » in the Pacific, at surface but also at subsurface. • Alternations periods « El Niño/ La Niña » from 3 to 7 years • Planetary consequences of the ENSO via the changes of the general circulation : Teleconnections. • Oceanic phenomenon partially predictable (causes of the onset of El Niño?) • Interactions ENSO/Pacific Decadal Oscillation(PDO), ENSO/MJO, MJO/Synoptic-scale

  11. El Nino 97 SST Source : NOAA/ NWS/NCEP/ Climate Prediction Center http://www.cpc.noaa.gov/products/precip/CWlink/MJO/enso.shtml/ Anomalies of + 5°c over East Pacific

  12. El Nino 97 : Dynamical anomalies height of the sea-level Source : figure extraite du site du Jet Propulsion Laboratory (JPL). site : http://sealevel.jpl.nasa.gov Sea-level anomalies height ‣ - 25 cm over West Pacific ‣ + 30 cm over East Pacific

  13. El Nino 97 : Source : NOAA/ NWS/NCEP/ Climate Prediction Center http://www.cpc.noaa.gov/products/precip/CWlink/MJO/enso.shtml/

  14. El Nino 97 : Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Subsurface Pacific structure and its evolution The area of strong vertical gradient of SST determines the thermocline whose depth varies also with the ENSO phase

  15. El Nino 97 : Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Subsurface Pacific structure and its evolution

  16. El Nino 97 : Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Subsurface Pacific structure and its evolution

  17. El Nino 97 : Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Subsurface Pacific structure and its evolution

  18. El Nino 97 : Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Subsurface Pacific structure and its evolution

  19. El Nino 97 : Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Subsurface Pacific structure and its evolution

  20. El Nino 97 : Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Subsurface Pacific structure and its evolution

  21. El Nino 97 : Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Subsurface Pacific structure and its evolution

  22. El Nino 97 : Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Subsurface Pacific structure and its evolution Back-up start animation

  23. El Nino 97 : red = 30°c blue= 8°c thermocline = between dark blue and pale blue, between 10 et 20°C, located at 600 ft in West Pacific and at 150 ft in East Pacific Subsurface Pacific structure and its evolution Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao 3D image coming from the french-american satellite Topex-Poséidon, (CNES-NASA) Surface waters measured by the HVRR sensor of the satellite Subsurface waters measured by stationary buoys , TAO

  24. El Nino 97 : Raising of the sea-level of 34 cm along the equatorial East Pacific because of the weakening of the trades winds Subsurface Pacific structure and its evolution The thermocline is flattened by the Kelvin wave (westerly wave) in the direction of the South American coasts. Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao

  25. 7.4 Description of the southern oscillation ‣ Southern Oscillation = periodic phenomeneon of reversal of the mean sea-level pressure (MSLP) pattern between the Central Pacific (Tahiti) and the Western Pacific (Darwin) associated with a displacement of the Walker cell. ‣ G. Walker (1932) has defined an index based on the difference of MSLP between Tahiti and Darwin which is : = monthly difference of MLSP between Tahiti and Darwin = monthly mean difference (1941-1980) of MLSP between Tahiti and Darwin = standard deviation of the monthly difference of MLSP between Tahiti and Darwin. The period of reference is 1941-1980 Darwin during an El Niño event during a La Niña event Tahiti

  26. 7.4 Description of the southern oscillation ‣ Determination of an El Niño event: the SOI must be lower than the lower quartile value of SOI ‣ Determination of a La Niña event : the SOI must be higher than the upper quartile value of SOI Darwin Tahiti

  27. Source : NOAA/ NWS/NCEP/ Climate Prediction Center. Site : http://www.cpc.noaa.gov/products/analysis_monitoring/bulletin/figt1.html

  28. Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao 7.5 El Niño : climatic changes over Pacific

  29. Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao 7.5 El Niño : climatic changes over Pacific

  30. Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao 7.5 El Niño : climatic changes over Pacific

  31. Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao 7.5 El Niño : climatic changes over Pacific

  32. Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao 7.5 El Niño : climatic changes over Pacific

  33. Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao 7.5 El Niño : climatic changes over Pacific

  34. ITCZ Indonesian monsoon 7.5 El Niño : climatic changes over Pacific trades winds SPCZ ITCZ trades winds SPCZ Source : d’après Trenberth, 91a Normal year (top), El Niño (bottom)

  35. Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao Westerly anomalies 7.5 El Niño : climatic changes over Pacific El Nino Easterly anomalies = trades strenghtened la Nina El Nino la Nina

  36. Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao 7.5 El Niño : climatic changes over Pacific El Nino la Nina El Nino la Nina

  37. 7.5 ENSO : climatic changes over Pacific Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao

  38. 7.5 La Niña : climatic changes over Pacific La Niña : The westerly subtropical jet (STJ) is less zonal than usual: upper westerlies over the Equatorial East Pacifique are strenghtened (+10 m/s). As upper westerlies acts as a Rossby canal duct , these westerly anomalies are conducive to favour the equatorward propagation of the Rossby waves. It’s the opposite for El Niño events since the STJ is more zonal than usual (figure not shown) Source :NOAA/PMEL/TAO

  39. 7.5 El Niño : climatic changes over North Africa (northen winter) ⇨ drier over Maghreb Source : figure from website IRI (International Research Institute For Climate and Society) http://iri.columbia.edu/

  40. 7.5 El Niño : climatic changes for the African monsoon ⇨ rain monsoon weakened Source : figure from website IRI (International Research Institute For Climate and Society) http://iri.columbia.edu/

  41. 7.5 La Niña : climatic changes for the African monsoon ⇨ rain monsoon enhanced Source : figure from website IRI (International Research Institute For Climate and Society) http://iri.columbia.edu/

  42. 7.6 Teleconnections : planetary consequences(rain and T) El Niño (december to february) Sources : d’après Ropelewski et Halpert, 1987 et 1989

  43. 7.6 Teleconnections : planetary consequences(rain and T) El Niño (june to august) Sources : d’après Ropelewski et Halpert, 1987 et 1989

  44. 7.6 Teleconnections : planetary consequences(rain and T) La Niña (december to february) Sources : d’après Ropelewski et Halpert, 1987 et 1989

  45. 7.6 Teleconnections : planetary consequences(rain and T) La Niña (june to august) Sources : d’après Ropelewski et Halpert, 1987 et 1989

  46. 7.7 Seasonal forecast of SST (CEP) Source : figures extraites du site du CEP

  47. 7.7 Seasonal forecast of the CEP ‣ These seasonal forecasts (1 to 6 months) of the SST (products called ‘Niño Plumes’) are available on the CEP web site : http://www.ecmwf.int/products/forecasts/d/charts/seasonal/forecast/

  48. El Niño references: TAO refereed journal articles and other TAO papers. • Hayes, S. P., L. J. Mangum, J. Picaut, A. Sumi, and K. Takeuchi, 1991 : TOGA-TAO: A moored array for real-time measurements in the tropical Pacific Ocean’. Bull. Am. Meteorol. Soc., Vol.72, p.339-347 • Lee, Martin E., and helton, Dudley, Oceanic Kevin/rossby Wave Infleunce on North American West COast Precipitation, NOAA Tecnhical Memorandum (NWS, WR-253) • McPhaden, M.J., 1993 : TOGA-TAO and the 1991-93 El Niño-Southern Oscillation Event. Oceanography, Vol.6, p.36-44 • NOAA Reports to the Nation – El Niño and Climate Prediction • Philander, S. G. H., 1990: El Nino, La Nina and the Southern Oscillation. Academic Press, San Diego, CA, 289 p. • Ropelewski C. F. et Halpert M. S., 1987 : ‘Global and Regional scale précipitations and temperature patterns associated with El Nino/Southern Oscillation’. Mon. Wea. Rev., Vol. 115, p. 1606-1626 • Ropelewski C. F. et Halpert M. S., 1989 : ‘Précipitations patterns associated with the high index of the Southern Oscillation’. J. Clim, Vol.2, p.268-284 References (1)

  49. - Trenberth , K. E., 1991a : General characteristics of El Nino-Southern Oscillation. Teleconnections Linking Worlwide Climate Anomalies. M. Glantz, R.W. Katz, and N. Nicholls, Eds., Cambridge University Press, p.13-41 References (2)

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