par- 19 mai 2008
vendredi 23 mai à 13h30
Detection of sub-mesoscale vortices In the northern current of the Mediterranean Sea
Alexandre Allou, doctorant au LOPB, présentera un séminaire le vendredi 23 mai à 13h30 en salle de réunion du COM à Luminy :
A boundary current following the isobaths and guided by the slope can sometimes be perturbated by instabilities. These one may degenerate in vortices which can be considered to some extent as solitary waves. These vortices are created by small perturbations of the current, and maintain themselves with time because of the energy the current gradients supply to them. Different structures of limited and localized time of duration had been evidenced at the occasion of the analysis of the results issued from a current measurement field campaign organized in a coastal area of the Mediterranean sea. The shape of the current velocity power spectral density before and after the wave occurs has been studied by a time frequency approach. This permit us to compare several methods and to evaluate their respective efficiency in order to detect the mesoscale and sub- mesoscale vortex in the Mediterranean northern current. The relevance of spectral methods are discussed comparing to other methods based on kinematic properties of the vortex structures.