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Accueil > Actualités > Séminaires > Séminaires 2018

Mardi 12 juin 2018 à 11h00 en amphi K118

Yves Morel, OMP/LEGOS, Toulouse

Titre : Interaction d’un tourbillon océanique avec la couche limite de surface : impact du stress de vent sur sa propagation et proposition d’un index pour distinguer les tourbillons intensifiés en sub-surface.
Title : Interaction of oceanic vortices with the surface layer :
- Influence of the wind stress of surface and subsurface vortices
- Identification of subsurface vortices

Contact : Eletta Negretti (Equipe MEIGE)

Résumé/Abstract : The general subject of the seminar is the signature and interaction of an oceanic (mesoscale) vortex with the surface layer. We will concentrate on the displacement of a vortex under the influence of the wind stress
and we will also address the possibility to detect subsurface intensified vortices using their surface signature.
I will first review a few basic principle concerning the dynamics of oceanic vortices (potential vorticity and dipolar structures).
Then I will talk about the influence of a constant wind on the displacement of a vortex. The well known Ekman current develops in the surface layer and is responsible for a transport perpendicular to the wind : the Ekman drift. We use a simplifiied 2 layer model to evidence an additional process, which is as strong as the Ekman drift. Frictionnal effects, associated with the wind stress, are indeed shown to modify the (potential) vorticity structure of the vortex. This diabatic effect is shown to act on the propagation of non linear vortices. It is shown that this effect drastically reduces the effect of the Ekman drift for surface intensified vortices, while extending its effect to subsurface vortices. It also generates along wind propagation, whose sign depends on the vortex characteristics (cyclonic/anticyclonic and surface/subsurface intensified). The understanding of the dynamics of this process can be predicted using analytical/physical arguments.
We then investigate the possibility of distinguishing surface and subsurface-intensified oceanic vortices from surface fields only (which can be obtained from satellite observations). A simple index, based on the ratio of the sea surface temperature anomaly and the sea level anomaly, is proposed. While the index is
expected to give perfect results for isolated vortices, we show that in a complex environment, errors can be expected, in particular when strong currents exist in the vicinity of the vortex. The validity of the index is then analyzed using results from a realistic regional circulation model of the eastern Pacific, where both surface
and subsurface eddies coexist.