HH20 vs. 2L20 dans les tropiques Etat moyen SST vs. obs.

HH20 vs. 2L20 dans les tropiques

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Etat moyen SST vs. obs









Etat moyen Taux vs. obs









Diff etat moyen SST/Taux HH20-2L20

Variabilité interannuelle

2L20NCEP

Pas assez de réponse en vent aux anomalies de SST









Variabilité interannuelle





2L20

Obs

HH20

Higher atmosphere resolution(2.5x1.8 vs. 3.75x2.5)

A"HiRes"

NCEP

ACTRL

Clear improvement of wind variability (Niño 4)

Higher atmosphere resolution

1. Larger El Niño variability (+ 15% amplitude)2. Slightly larger ICS, larger non-linearity

CTRL "HiRes"

<SST>

ICS

HH20 vs 2L20 conclusions

• Pas de révolution dans état moyen et SC (mais légères améliorations)

• Nette amélioration de la variabilité en vent dans le Pacifique central (même si progrès encore possibles !

• Du coup, El Niño est plus fort (+15% - trop fort en fait)

• Suite:• regarder VV20 et 1 degré• comprendre trop faible variabilité en vent (runs IFC)• analyse feedback flux de chaleur

Impact of correction on wind stress variability (IFC)

1. Anot much corrected (via SSTA)

2. Over correction O as « non-linearity » added during

growing phase via

AIFC

ACTRL

ONCEP

SC SC

SC SC

Radiative feedbacks

Analysis of 9 AMIP forced AGCM (IPCC AR4) (Sun al. 2006)

• Too weak negative net feedback from atmosphere leads to unrealistically high sensitivity to small flux errors

• Main contributors: cloud albedo and atmosphere transport feedbacks

• Linked to a too strong water vapour feedback (underestimation of equatorial precipitation response)

Response of net surface heating to ENSO warming

El Niño in coupled GCMs – Eric Guilyardi – WGNE/PCMDI, San Francisco – Feb 2007

Impact of U*(Passage du courant)

Tropical Instability Waves

U*=0 U*0

T30

T106

SST (shading) + wind div.• TIW “seen” by T106

• U* (TIW) “seen” by wind stress calculation

Navarra et al. 2006

U*=0 vs. U*0• Impact on tropical variability shown in SINTEX-F (T106)

U*=0

U*0

Reduced CS and Tau variability,Slightly reduced El Niño amplitude

SST correlation with nino3 SST

(Luo, Masson et al., 2006)

Impact on mean state

IPSL

INGV

SST Taux

Impact on mean state SST errorsDiff. with obs

IPSL

INGV

CTRL U* run

Impact on interannual variability (IPSL)CTRL U* run

Oce

anA

tmos

Impact on interannual variability (INGV)CTRL U* run

Oce

anA

tmos

• Including U* in wind stress computation:– slightly slows down trade winds, mostly in

spring (good)– slightly warms west Pacific (good)– slightly reduces El Niño amplitude (why ?)

Preliminary conclusions of U* runs

Impact on seasonal cycle at equator

IPSL

INGV

SST Taux

Impact on SST seasonal cycle at equator

IPSL

INGV

Diff. with obsCTRL U* run

HH20 vs. 2L20 dans les tropiques Etat moyen SST vs. obs.

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