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

Etat moyen Taux vs. obs

Diff etat moyen SST/Taux HH20-2L20

Variabilité interannuelle 2L20 NCEP 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   A  CTRL 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 " 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)  A   not much corrected (via SSTA) 2.Over correction  O  as « non-linearity » added during growing phase via  A  IFC  A  CTRL  O   NCEP          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 SSTTaux

Impact on mean state SST errors Diff. with obs IPSL INGV CTRLU* run

Impact on interannual variability (IPSL) CTRLU* run Ocean Atmos

Impact on interannual variability (INGV) CTRLU* run Ocean Atmos

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 SSTTaux

Impact on SST seasonal cycle at equator IPSL INGV Diff. with obs CTRLU* run