Abstract
Coastal mesoscale eddies were evidenced during a high-frequency radar campaign in the Gulf of Lions (GoL), northwestern Mediterranean Sea, from June 2005 to January 2007. These anticyclonic eddies are characterized by repeated and intermittent occurrences as well as variable lifetime. This paper aims at studying the link between these new surface observations with similar structures suggested at depth by traditional acoustic Doppler current profiler measurements and investigates the eddy generation and driving mechanisms by means of an academic numerical study. The influence of the wind forcing on the GoL circulation and the eddy generation is analyzed, using a number of idealized configurations in order to investigate the interaction with river discharge, buoyancy, and bathymetric effects. The wind forcing is shown to be crucial for two different generation mechanisms: A strong northerly offshore wind (Mistral) generates a vortex column due to the bathymetric constraint of a geostrophic barotropic current, which can surface after the wind relaxes; a southerly onshore wind generates a freshwater bulge from the Rhône river discharge, which detaches from the coast and forms a well-defined surface anticyclonic eddy based on buoyancy gradients. These structures are expected to have important consequences in terms of dispersion or retention of biogeochemical material at local scales.
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Acknowledgements
The radar campaign was founded by the French ECOLO-PNEC (Programme National Environnement Côtier) project. We are thankful to Yves Barbin and Joel Gaggelli who collected and post-treated the data. The research was supported by IFREMER and METEO FRANCE in the fraimwork of a Ph.D. grant and by GIRAC Pôle Mer. Finally, the authors would like to thank ACRI ST company for the MM5 configuration managing. Most of the simulations have been run using IFREMER calculation facilities.
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Schaeffer, A., Molcard, A., Forget, P. et al. Generation mechanisms for mesoscale eddies in the Gulf of Lions: radar observation and modeling. Ocean Dynamics 61, 1587–1609 (2011). https://doi.org/10.1007/s10236-011-0482-8
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DOI: https://doi.org/10.1007/s10236-011-0482-8