Laboratoire d’Océanographie Physique et Biogéochimique
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Séminaire d’Alexandre Stegner
par - 4 février 2008
Lundi 4 février 11h30
Centre Ifremer de La Seyne/mer
Dynamique des tourbillons le long du talus
Alexandre Stegner, chargé de recherche CNRS au Laboratoire de Météorologie Dynamique présentera un séminaire le lundi 4 février à 11h30 en salle de réunion Porquerolles du Centre Ifremer de La Seyne/mer :
"Dynamique des tourbillons le long du talus"
The first in situ observations of the EGYPT (Eddies and GYres Paths Tracking) programme in the eastern basin of the Mediterranean, backed by thermal images, reveal a large meso-scale anticyclone, propagating westward along the Libyo-Egyptian shelf ( ie in a direction opposite to the mean circulation). Surface drifters trajectories combined with a CTD transect quantify the horizontal and the vertical structure of this surface-intensified anticyclone. The observed westward drift speed is significantly faster than expected from the beta-effect only. To investigate this specific eddy dynamics we used a two-layer beta-plane model with steep continental slope and zonal boundary. An integral momentum balance for the upper layer is used to derive the vortex center velocity assuming a circular dome interface at the leading order. This approach reduces the problem to the calculation of the deep-flow pattern, depending on the interface shape and topography. When the topographic slope beneath the eddy changes rapidly most of the deep-flow pattern is shifted offshore. The corresponding anticyclonic deep-flow feedback provides additional along-slope propagation. This mechanism was also studied in laboratory experiments. A significant drift acceleration of anticyclonic vortices was found when a steep topography is introduced, in good agreement with the perturbation theory.
