Mesoscale vortices in the Ligurian Sea and their effect on coastal upwelling processes

We study numerically the dynamics of intense anticyclonic eddies in the Ligurian Sea (NW Mediterranean Sea). To this end, we use the Regional Ocean Modeling System (ROMS) with a resolution of 3 km for a domain covering the whole Ligurian Sea, with an embedded child grid covering the northwestern part of Ligurian Sea at resolution 1 km. The model is forced with daily boundary conditions obtained from the MFS dataset for the year 2006 at the open lateral boundaries. Surface heat and evapotranspiration fluxes are provided by the monthly climatological dataset COADS at 1/2 spatial resolution. For wind forcing, we consider two configurations. In the first setting, the model is forced by the COADS climatological monthly mean wind stresses; in a second configuration, the model is forced by the daily mean wind stresses provided by a mesoscale meteorological model for the area of interest in the year 2006. The latter setting shows the formation of intense anticyclonic eddy structures in the coastal area, generated by the variable winds and by the interaction of transient currents with bottom and coastal topography (in the NW part of the Ligurian Sea). Comparison of model output with satellite SST data shows definite agreement between numerical results and observations. Analysis of the simulation results over the whole year 2006 and of SST satellite images in 2006 and 2007 indicates that coastal anticyclonic eddies are of common occurrence in the Ligurian Sea, with several events per year, mainly concentrated in autumn and winter. The eddies are characterized by a complex pattern of intense vertical velocities and induce strong, long-lasting coastal upwelling events. For this reason, anticyclonic vortices in the coastal area can generate bursts of nutrient input in the euphotic layer and contribute to the fertilization of the Ligurian Sea, with potentially important effects on the dynamics of phytoand zooplankton. (C) 2011 Elsevier B.V. All rights reserved.