The Gulf of Lion area is characterised by strong Northwesterly winds, Tramontane and Mistral. In winter, the turbulent mixing induced by wind tends to homogeneize the water column. Over the shelf, especially in the western part (relatively less sensitive to buoyancy effects due to the Rhone river outputs), the barotropic component of the circulation can prevail. The depth-averaged current is influenced by the bottom slope and the wind curl. Eddy circulations over the shelf were observed during the FETCH experiment (Gulf of Lion, winter 1998). Simulations showed that the spatial distribution of winds (wind curl) were responsible for theses particular oceanic features.

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Observation and modelisation of the winter coastal oceanic circulation in the Gulf of Lions under wind conditions influenced by the continental orography (FETCH experiment)

Abstract : Hydrological and currentmeter observations were collected on the continental shelf and slope of the Gulf of Lion during the FETCH experiment (13 March to 15 April 1998). Results from the first part of the cruise, characterized by strong northern winds, are presented. The hydrological structures evidence well-mixed water masses on the eastern and western ends of the shelf. In the central part, the situation is more complex, with the influence of the Rhône river's freshwater plume in the first 40 m of the water column and, closer from the bottom, with the confrontation of downwelled coastal cold water and upwelled warmer and saltier slope water. Current measurements show the path of the cyclonic circulation along the slope, which is part of the general circulation of the western Mediterranean, and suggest the presence of large and temporary eddies on the shelf. This oceanic circulation is simulated with a free surface three-dimensional model using realistic forcing. The model outputs are in agreement with the main hydrological and circulation patterns. The results further indicate that coastal eddies are generated by the mesoscale structure of the wind field.

References : Estournel C., Durrieu de Madron X., Marsaleix P., Auclair F., Julliand C. and R. Vehil, 2003. Observation and modelisation of the winter coastal oceanic circulation in the Gulf of Lions under wind conditions influenced by the continental orography (FETCH experiment). Journal of Geophysical Research 108, C3, pages 7-1 to 7-18. doi:10.1029/2001JC000825

2000

Claire Dufau-Julliand Document pdf

Modélisation de la circulation océanique dans le Golfe du Lion: exploitation de la campagne FETCH-MOOGLI

LA

Dir. : Patrick Marsaleix