Nos tutelles


Nos partenaires


Accueil du site > Évènements > Séminaires > Séminaires IRPHE > Archives IRPHE > 2017

Mercredi 25 Janvier 2017/ IRPHE

publié le , mis à jour le

Séminaire exceptionnel IRPHE

Meanders or eddies generation from an unstable coastal current above the shelf slope : Laboratory experiments and numerical modeling

Orateur : Alexandre Stegner
LMD, Ecole Polytechnique, Paris

Résumé : 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. The impact of the shelf bathymetry leads to different regimes of instability of coastal currents that can both enhance or prevent the cross-shore transport. While keeping unchanged a coastal jet, we tested its unstable evolution for various depth and topographic slopes. Unlike standard linear stability analysis devoted to the very first stage of instability we focus on the non-linear end state, i.e. the formation of coastal eddies or meanders, to classify the various dynamical regimes. Two dimensionless numbers are used to quantify the parameter space of theses various regimes : the vertical aspect ratio gamma and the topographic parameter Tp, which is defined as the ratio of the topographic Rossby waves speed over the jet speed and is proportional to the shelf slope. We identify three distinct dynamical regimes : the quasi-stable jet configuration, the along-shore propagation of coastal meanders and the formation of coherent eddies. Our results show that Tp is the key parameter that controls the non-linear saturation of the unstable coastal current, while the gamma parameter mainly controls the transition from meanders to coherent eddies. This work emphasizes the limitations of linear stability analysis to classify eddy formation, over the shelf slope, because it does not account for the non-linear saturation which control the formation of coherent eddies or coastal meanders.

Date et Lieu : le Mercredi 25 Janvier 2017 à 11h00, salle de séminaire IRPHE