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HH20 vs. 2L20 dans les tropiques

HH20 vs. 2L20 dans les tropiques. Etat moyen SST vs. obs. Etat moyen Taux vs. obs. Diff etat moyen SST/Taux HH20-2L20. Variabilit é interannuelle. NCEP. 2L20. Pas assez de r é ponse en vent aux anomalies de SST. Variabilit é interannuelle. 2L20. Obs. HH20.

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HH20 vs. 2L20 dans les tropiques

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

  2. Etat moyen Taux vs. obs

  3. Diff etat moyen SST/Taux HH20-2L20

  4. Variabilité interannuelle NCEP 2L20 Pas assez de réponse en vent aux anomalies de SST

  5. Variabilité interannuelle 2L20 Obs HH20

  6. Higher atmosphere resolution(2.5x1.8 vs. 3.75x2.5) NCEP A"HiRes" ACTRL Clear improvement of wind variability (Niño 4)

  7. Higher atmosphere resolution CTRL "HiRes" <SST> ICS Larger El Niño variability (+ 15% amplitude) Slightly larger ICS, larger non-linearity

  8. 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

  9. Impact of correction on wind stress variability (IFC) SC SC O NCEP AIFC ACTRL Anot much corrected (via SSTA) Over correction O as « non-linearity » added during growing phase via SC SC

  10. Radiative feedbacks Analysis of 9 AMIP forced AGCM (IPCC AR4) (Sun al. 2006) • Too weak negative net feedback from atmosphereleads 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

  11. Impact of U* (Passage du courant)

  12. Tropical Instability Waves SST (shading) + wind div. • TIW “seen” by T106 T30 • U* (TIW) “seen” by wind stress calculation U*=0 U*0 T106 Navarra et al. 2006

  13. U*=0 vs. U*0 • Impact on tropical variability shown in SINTEX-F (T106) SST correlation with nino3 SST U*=0 U*0 Reduced CS and Tau variability, Slightly reduced El Niño amplitude (Luo, Masson et al., 2006)

  14. Impact on mean state SST Taux IPSL INGV

  15. Impact on mean state SST errors Diff. with obs CTRL U* run IPSL INGV

  16. Impact on interannual variability (IPSL) CTRL U* run Ocean Atmos

  17. Impact on interannual variability (INGV) CTRL U* run Ocean Atmos

  18. Preliminary conclusions of U* runs • 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 ?)

  19. Impact on seasonal cycle at equator SST Taux IPSL INGV

  20. Impact on SST seasonal cycle at equator Diff. with obs CTRL U* run IPSL INGV

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