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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/eln
ino/theme/nino.htm
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7.1 Oceanic climatology
SST
Source NOAA/PMEL/TAO. Site http//www.pmel.noa
a.gov/toga-tao
Sea Surface Temperature
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7.1 Oceanic climatology SST
Source NOAA/PMEL/TAO. Site http//www.pmel.noa
a.gov/toga-tao
Pourquoi des eaux plus Fraiches sur les cotes est
des continents ?
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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 dEkman at
right angle to the right of the wind stress
In the southern hemisphere, Its the opposite
Ekman Transport at right angle to the left of
the wind stress
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7.1 Climatologie océanique Transport dEkman 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
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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
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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
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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 )

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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

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7.3 Principales caractéristiques dEl 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

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

• Subsurface Pacific structure and its evolution

Source NOAA/PMEL/TAO. Site
http//www.pmel.noaa.gov/toga-tao
The area of strong vertical gradient of SST
determines the thermocline whose depth varies
also with the ENSO phase
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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

• 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

• 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

• 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

• 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

• 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

• 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

• Subsurface Pacific structure and its evolution

Source NOAA/PMEL/TAO. Site
http//www.pmel.noaa.gov/toga-tao
Back-up start animation
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El Nino 97

• Subsurface Pacific structure and its evolution

red 30c blue 8c thermocline between dark
blue and pale blue, between 10 et 20C,
located at 600 ft in West Pacific and at 150 ft
in East Pacific
Source NOAA/PMEL/TAO. Site http//www.pmel.noa
a.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
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El Nino 97

• Subsurface Pacific structure and its evolution

Raising of the sea-level of 34 cm along the
equatorial East Pacific because of the weakening
of the trades winds
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
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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
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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
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Source NOAA/ NWS/NCEP/ Climate Prediction
Center. Site http//www.cpc.noaa.gov/products/an
alysis_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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• 7.5 El Niño climatic changes over Pacific

ITCZ
Indonesian monsoon
trades winds
SPCZ
ITCZ
trades winds
SPCZ
Source daprès Trenberth, 91a
Normal year (top), El Niño (bottom)
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• 7.5 El Niño climatic changes over Pacific

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

Source NOAA/PMEL/TAO. Site http//www.pmel.noa
a.gov/toga-tao
El Nino
la Nina
El Nino
la Nina
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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
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. Its the
opposite for El Niño events since the STJ is more
zonal than usual (figure not shown)
Source NOAA/PMEL/TAO
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7.5 El Niño climatic changes over North
Africa (northen
winter)
? drier over Maghreb
Source figure from website IRI (International Re
search Institute For Climate and Society)
http//iri.columbia.edu/
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7.5 El Niño climatic changes for the African
monsoon
? rain monsoon weakened
Source figure from website IRI (International Re
search Institute For Climate and Society)
http//iri.columbia.edu/
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7.5 La Niña climatic changes for the African
monsoon
? rain monsoon enhanced
Source figure from website IRI (International Re
search Institute For 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 daprès Ropelewski et Halpert, 1987 et
1989
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7.6 Teleconnections planetary consequences
(rain and T)
El Niño (june to august)
Sources daprès Ropelewski et Halpert, 1987 et
1989
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7.6 Teleconnections planetary consequences
(rain and T)
La Niña (december to february)
Sources daprès Ropelewski et Halpert, 1987 et
1989
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7.6 Teleconnections planetary consequences
(rain and T)
La Niña (june to august)
Sources daprès 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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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/s
easonal/forecast/
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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

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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