Accueil > Actualités > Séminaires > Séminaire de Takahito Kataoka


Titre : Wind-Mixed layer-SST Feedbacks in a tropical air-sea coupled system: Application to the Atlantic
Nom du conférencier : Takahito Kataoka
Son affiliation : JAMSTEC/YES
Laboratoire organisateur : LMD
Date et heure : 06-11-2019 11h00
Lieu : Département de Géosciences de l'ENS, en Salle Froidevaux - 314 - 24 rue Lhomond - Paris - 3ème étage (bouton ascenseur 6)
Résumé :

The ocean-atmosphere feedback associated with the thermodynamic coupling among wind speed, evaporation, and sea surface temperature (SST), called the wind-evaporation-SST (WES) feedback, contributes to the cross-equatorial SST gradient over the tropical oceans. By conducting an eigenanalyses of simple linear air-sea coupled models, it is shown that two additional feedback processes are present when the variable oceanic mixed layer depth (MLD) is considered. The horizontal structures of the leading modes are similar to the WES mode, which shows a meridional dipole in the SST anomalies straddling the equator with cross-equatorial wind anomalies that represent the weakening/strengthening of the trade winds over the warm/cool SST anomalies. The coupling of the variable MLD with winds and SST more than doubles the growth rate of the WES mode and enhances the equatorward propagation of the coupled disturbances.
The identified feedbacks operate as follows. The weaker winds associated with warm SST anomalies shoal the mixed layer through suppressed turbulent mixing, which causes the mixed layer to be more sensitive to the climatological shortwave radiation and amplifies the initial positive SST anomalies. Likewise, deepening of the mixed layer due to stronger winds acts to maintain the negative SST anomaly on the other side of the dipole. The MLD anomalies can also be generated by the buoyancy flux anomaly related to the wind-induced latent heat flux anomaly.

The anti-phase relationship between the SST and MLD anomalies seen in the simple model bears some resemblance to that which is observed in the observations and a state-of-the-art coupled model (MIROC6) during the Atlantic meridional mode.

Also, results from an ongoing work on yet another coupled feedback involving freshwater flux, which utilize a theoretical model and sensitivity experiments of fully coupled model, will be mentioned if time allows.

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