Transcript The ENSO : El Niño and the Southern Oscillation J.P. Céron (Météo-France) and R.

The ENSO : El Niño and the
Southern Oscillation
J.P. Céron (Météo-France) and
R. Washington (Oxford University)
The fundamentals (1)
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Mean circulation in Tropical regions deeply
influenced by large scale organised convection
(Hadley-Walker divergente circulations),
Energetic exchanges mainly driven by the mean
circulation in tropical regions,
Mean circulation mainly driven by the evolution of
boundary conditions (particularly SST but also
continentale surface conditions),
Feedbacks and coupling processes between the
atmospheric circulation and the boundary
conditions at the surface.
The fundamentals (2)
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Ocean/atmosphere
 Surface fluxes (sensible, latent, momentum)
Ocean/atmosphere interactions
 Convergences/divergences + wind stress
(coupled dynamic)
 Ekmann Transport
 Coupling processes
Oceanic circulation
 Surface and sub-surface currents
 Upwelling, downwelling
ATMOSPHERE
Equation of
Water Vapour
Thermodynamic
Equation
Equation of
Motion
Radiation
Evaporation
Heat
Precipitation
Radiative transfer
Salt Equation
Thermodynamic
Equation
Ice Equation
OCEAN
Surface Stress
Equation of
Motion
Ekman Transport
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Wind friction effect at the surface (wind stress),
Action of the Coriolis force on the oceanic fluide,
Resulting Ekman transport, right to the wind in
the Northern hemisphere and left in the Southern
hemisphere,
Coupling between vertical and horizontal motions
through the continuity equation.
The
importance of
wind forcing
The importance
of Solar forcing
and evaporation
fluxes
The
relationship
between the
SST forcing
and the
clouds
Historical chronology
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Phase opposition in the surface pressure pointed out at
Sydney and Buenos Aires (Hildebrandsson – 1897)
Southern Oscillation (P,T,RR) – G. Walker (~1920)
Relationship between Pacific SST and SO (Bjerkness –
1966, 1969 – discovering the Teleconnexion notion),
« Build-up » from Wyrtki (1975-1979)
Niño composite and seasonnal phase lock – Rasmusson
and Carpenter (1982),
Ocean/atmosphere coupled models (1980 ….),
Theoritical developpments (1980 …)
Theoritical Developpments
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« Build-up » from Wyrtki
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Delayed Oscillator
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Driving of ocean conditions by atmosphere (trade wind relaxation –
warm SST redistribution from West to East).
Rossby waves reflexion in Kelvin waves (West boundary)
conducting to a deepening of the thermocline. Kelvin waves
reflexion (East boundary). Alternately warm («downwelling» kelvin
wave) and cold anomalies («upwelling» kelvin wave).
Coupled Instabilities
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SST - thermocline relationship (positive coupling process
associated with a surface wind convergence),
Low frequency coupled Mode (periods 3 to 4 years and 6 month),
«SST mode» - SST mean gradient zonal advection by the current
disturbances – Temperature vertical mean gradient advection by
vertical motion disturbances – modulated vertical advection by the
Mean Equatorial Upwelling.
Salt Barrier role – shifting of the Warmpool’s Eastern boundary in
relationship with the SST gradient zonal advection
The ENSO
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Ocean/Atmosphere coupling system,
ENSO main variability source of the climatic system at
interannual timescales,
« El Niño/La Niña » oceanic behaviour in the Pacific, both
in surface and sub-surface,
Caracteristic periods from 3 to 7 years and tendancy to
alternate « El Niño/ La Niña » events.
Planetary influence through general circulation
modifications. Teleconnections.
Oceanic behaviour partly predictable (Starting up causes of
the process?)
Interactions ENSO/PDO, ENSO/MJO, MJO/Synoptic
The ENSO (1)
El Niño 97
Surface Temperature
Dynamical Height
Thermocline depth
The ENSO (2)
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Surface Oceanic currents
The ENSO (2)
The ENSO (2)
The ENSO (2)
The ENSO (3)
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The deep Oceanic structure and its evolution
The ENSO (3)
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The deep Oceanic structure and its evolution
The ENSO (3)
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The deep Oceanic structure and its evolution
The ENSO (4)
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The Ocean/Atmosphere coupling process
In the Western Pacific (156°E)
In the Central Pacific (155°O)
The ENSO (4)
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The Ocean/Atmosphere coupling process
In the Central Pacific (155°O)
In the Eastern Pacific (95°O)
The ENSO (5)
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Southern Oscillation description
Darwin
Tahiti
The ENSO (5)
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Southern Oscillation
description
SEP 97
NOV 88
The ENSO (6)
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Influence over the Pacific
El Niño year
Normal year
winter
La Niña year
spring
The ENSO (6)
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Influence over the Pacific
The ENSO (6)
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Influence over the Pacific
The ENSO (6)
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Influence over the Pacific
The ENSO (7)
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The planetary influence of El Niño (left) and La Niña (right)
The ENSO (8)
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The mid-latitude influence
The ENSO (9)
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El Niño influence over Africa (Boreal winter)
The ENSO (9)
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El Niño influence over Africa (Boreal summer)
The ENSO (9)
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La Niña influence over Africa (Boreal summer)
The ENSO (10)
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Los Niños y Las Niñas
Time evolution comparison of the 7 strongest Niños
The ENSO (10)
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Los Niños y Las Niñas
Time evolution comparison of the 7 strongest Niñas
The ENSO
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The predictability
The
E
N
S
O
The ENSO
The ENSO
The ENSO
The ENSO
The ENSO
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Influence over MJO
The decadal climatic variability
The decadal Pacific oscillation
Resume the ENSO
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The variability of the
Ocean/Atmosphere
system
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The coupled
modelisation