chap. 7 enso
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Chap. 7 ENSO
‣ To learn more about ENSO, see this web site http://www.educnet.education.fr/obter/appliped/elnino/theme/nino.htm
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
sommaire général
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Sea Surface Temperature
7.1 Oceanic climatology : SST
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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Pourquoi des eaux plusFraiches sur les cotes est des continents ?
7.1 Oceanic climatology : SST
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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7.1 Oceanic climatology :Ekman transport and coastal upwelling
Northern Hemisphere :Ekman transport d’Ekman at rightangle to the right of the wind stress
In the southern hemisphere, It’s the opposite : Ekman Transport at right angle to the leftof the wind stress
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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In the southern hemisphere, the Ekman transport is locatedat right angle to the left of thewind stress
Wind stress
Ekman transport
Peru
Chile
7.1 Climatologie océanique :Transport d’Ekman et upwelling côtier
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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Wind stress
Coastal Upwelling Equatorial undercurrent
7.1 Oceanic climatology :3D circulations in the Pacific
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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Sea level more elevated over West Pacific
7.1 Oceanic climatology : Sea-level
Source : figure extraite du site du Jet Propulsion Laboratory (JPL). site : http://sealevel.jpl.nasa.gov
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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 …)
7.2 Historical and theoretical developments
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« 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
7.2 Historical and theoretical developements
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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
7.3 Principales caractéristiques d’El Niño
et illustration avec El Niño 97
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El Nino 97El Nino 97
SST
Anomalies of + 5°c over East Pacific
Source : NOAA/ NWS/NCEP/ Climate Prediction Center http://www.cpc.noaa.gov/products/precip/CWlink/MJO/enso.shtml/
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El Nino 97 :El Nino 97 :Dynamical anomalies height of the sea-level
Sea-level anomalies height ‣ - 25 cm over West Pacific ‣ + 30 cm over East Pacific
Source : figure extraite du site du Jet Propulsion Laboratory (JPL). site : http://sealevel.jpl.nasa.gov
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El Nino 97 :El Nino 97 :
Source : NOAA/ NWS/NCEP/ Climate Prediction Center http://www.cpc.noaa.gov/products/precip/CWlink/MJO/enso.shtml/
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Subsurface Pacific structure and its evolutionEl Nino 97 :El Nino 97 :
The area of strong vertical gradient of SST determines the thermocline whose depth varies also with the ENSO phase
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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El Nino 97 :El Nino 97 :Subsurface Pacific structure and its evolution
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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El Nino 97 :El Nino 97 :Subsurface Pacific structure and its evolution
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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El Nino 97 :El Nino 97 :Subsurface Pacific structure and its evolution
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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El Nino 97 :El Nino 97 :Subsurface Pacific structure and its evolution
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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El Nino 97 :El Nino 97 :Subsurface Pacific structure and its evolution
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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El Nino 97 :El Nino 97 :Subsurface Pacific structure and its evolution
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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El Nino 97 :El Nino 97 :Subsurface Pacific structure and its evolution
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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El Nino 97 :El Nino 97 :
Back-upstart animation
Subsurface Pacific structure and its evolution
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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El Nino 97 :El Nino 97 :
3D image coming from the french-american satelliteTopex-Poséidon, (CNES-NASA)
Surface waters measured by the HVRR sensor of the satelliteSubsurface waters measured by stationary buoys , TAO
red = 30°cblue= 8°cthermocline = 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
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El Nino 97 :El Nino 97 :
The thermocline is flattened by theKelvin wave (westerly wave) in the directionof the South American coasts.
Raising of the sea-level of 34 cm along the equatorial East Pacificbecause of the weakening of the trades winds
Subsurface Pacific structure and its evolution
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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Tahiti
Darwin
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 :
xx
SOI
= 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
x
x
0SOI during an El Niño event
0SOI during a La Niña event
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Tahiti
Darwin
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
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Source : NOAA/ NWS/NCEP/ Climate Prediction Center.Site : http://www.cpc.noaa.gov/products/analysis_monitoring/bulletin/figt1.html
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7.5 El Niño : climatic changes over Pacific
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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7.5 El Niño : climatic changes over Pacific
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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7.5 El Niño : climatic changes over Pacific
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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7.5 El Niño : climatic changes over Pacific
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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7.5 El Niño : climatic changes over Pacific
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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7.5 El Niño : climatic changes over Pacific
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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Normal year (top), El Niño (bottom)
ITCZ
ITCZ
SPCZ
SPCZ
Indonesianmonsoon trades winds
trades winds
7.5 El Niño : climatic changes over Pacific
Source : d’après Trenberth, 91a
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El NinoWesterlyanomalies
la Nina
Easterlyanomalies = trades strenghtened
El Nino
la Nina
7.5 El Niño : climatic changes over Pacific
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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El Nino
la Nina
El Nino
la Nina
7.5 El Niño : climatic changes over Pacific
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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7.5 ENSO : climatic changes over Pacific
Source : NOAA/PMEL/TAO. Site : http://www.pmel.noaa.gov/toga-tao
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7.5 La Niña : climatic changes over Pacific
La Niña :The westerly subtropical jet (STJ)is less zonal than usual:upper westerlies overthe Equatorial East Pacifique arestrenghtened (+10 m/s).As upper westerlies acts as a Rossby canal duct , these westerly anomalies are conducive to favourthe equatorward propagation of the Rossby waves.
It’s the opposite forEl Niño events since theSTJ is more zonal than usual (figure not shown)
Source :NOAA/PMEL/TAO
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⇨ drier over Maghreb
7.5 El Niño : climatic changes over North Africa
(northen winter)
Source : figure from website IRI(InternationalResearch InstituteFor Climate and Society) http://iri.columbia.edu/
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⇨ rain monsoon weakened
7.5 El Niño : climatic changes for the African monsoon
Source : figure from website IRI(InternationalResearch InstituteFor Climate and Society) http://iri.columbia.edu/
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⇨ rain monsoon enhanced
7.5 La Niña : climatic changes for the African monsoon
Source : figure from website IRI(InternationalResearch InstituteFor Climate and Society) http://iri.columbia.edu/
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7.6 Teleconnections : planetary consequences (rain and T)
El Niño (december to february)
Sources : d’après Ropelewski et Halpert, 1987 et 1989
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El Niño (june to august)
7.6 Teleconnections : planetary consequences (rain and T)
Sources : d’après Ropelewski et Halpert, 1987 et 1989
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La Niña (december to february)
7.6 Teleconnections : planetary consequences (rain and T)
Sources : d’après Ropelewski et Halpert, 1987 et 1989
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La Niña (june to august)
7.6 Teleconnections : planetary consequences (rain and T)
Sources : d’après Ropelewski et Halpert, 1987 et 1989
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7.7 Seasonal forecast of SST (CEP)
Source : figures extraites du site du CEP
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‣ 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/
7.7 Seasonal forecast of the CEP
References (1)
- 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 (2)
- 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