Eddy measurements, coastal turbulence and statistics in the gulf of Lions

Abstract. The advances in radar sensors may be applied to study the flow in the Region of Fresh Water Influence (ROFI) region of the ocean. The Synthetic Aperture Radar (SAR) is a useful tool that may be used to study both marine water dynamics and its pollution. Oil spills and natural slicks may be detected and processed with advanced computer techniques to reveal vortex dynamics and turbulence spectral characteristics of the complex eddy and current interaction in the ocean surface, more than 300 SAR images of the North-west Mediterranean Sea area taken between December 1996 and December 1998 were analyzed. A total of 255 eddies were detected under convenient environmental conditions and we analyzed statistically the appearance, size, shape and position of vortices in the test area. We find that the maximum size of the eddies detected near the coast is limited by the Rossby deformation radius and that there is a decrease in size in the coastal waters in the direction of the Liguro-Provenzal current with the largest eddies occurring near the cape of Rosas. Near the Rhone and Ebro rivers, high discharges also contribute to eddy forcing, coastal radar measurements confirm the SAR observations. The role of submarine canyons in the vortex generation is also confirmed due to the asymmetry of their distribution with respect to the thalwegs. It is demonstrated that useful information of a geometrical nature obtained by SAR satellite images may be used to estimate relevant dynamical parameters of coastal flows.