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Jeudi 3 juillet - Meso and sub meso scale dynamics of coastal current along the shelf slope

Par semsou — Dernière modification 24/06/2014 10:57
Quand ? Le 03/07/2014,
de 14:00 à 15:00
Où ? Salle Jules Verne
Participants Alexandre Stegner (LMD, Polytechnique)
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Alexandre Stegner (LMD, Polytechnique)



Titre:  Meso and sub meso scale dynamics of coastal current along the shelf slope.


Abstract:

The impact of shelf slope on the stability of coastal currents and the nonlinear formation of coastal meanders and eddies are investigated by linear analysis, numerical simulations and laboratory experiments. The simulations were performed using the Regional Oceanic Modeling System (ROMS) and the laboratory experiments were achieved on the UME-LMD rotating platform. High resolution is achieved in both investigations (PIV measurements and numerical grid) in order to quantify accurately the meso and the sub meso scale structures. Our results exhibit a new generalized topographic parameter Tp which includes the To parameter (ratio between the shelf slope and the isopycnal slope of the current) which was found to be a relevant parameter in previous studies (Mechoso 1980 ; Isachsen, 2011; Pennel et al. 2011; Poulain et al. 2014). We have found that the shelf may induces three distinct dynamical regimes of instability for a gesotrophic coastal current. For weak values of the Tp parameter, the baroclinic instability induces large scale meanders leading to the formation of large meso scale anticyclones which escape from the coast. For moderate Tp values, the unstable wavelength decays and lead to the formation of both small scales cyclones and anticyclones trapped on the shelf. For finite Tp values a strong non-linear stabilisation occurs which prevents the formation of eddies, but weak perturbations induced by the barotropic shear instability are still active.

Application to coastal altimetry will be discussed.




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