CIRCULATION OF THE WESTERN MEDITERRANEAN - FROM GLOBAL TO REGIONAL SCALES

A free-surface, three-dimensional, primitive equation model has been i mplemented with a horizontal resolution of 4.6 km to study the ocean c irculation in the Gulf of Lions at time scales ranging from weeks to s easons. Numerical experiments have been conducted, in which the region al model is nested into a basin-scale model of the whole western Medit erranean. The global model is operated with a relatively coarse resolu tion (16 km) and provides boundary conditions at the open-sea boundari es of the regional domain. There is, however, no Feedback loop from th e regional to the global model. The simulations are consistently drive n with atmospheric fluxes computed from the output of the French PERID OT meteorological forecasting system, between August 1988 and 1989. In addition to the initial conditions, in situ measurements of temperatu re and salinity are assimilated in the simulation of the general circu lation, adopting a simple nudging technique to prevent an excessive dr ift of the model against climatology. The response of the regional mod el below and above the thermocline is discussed in the context of the prevailing meteorological situations. Some experiments give indication s that a double-gyre system may develop from wind regimes that exhibit a cyclonic/anticyclonic wind stress curl. Advection-diffusion of pass ive tracers are also examined on the basis of the local hydrodynamic f eatures, because this work has been conceived with the aim of determin ing the physical conditions in which ecological and biochemical proces ses develop at the interface between river mouths and the open ocean. (C) 1997 Elsevier Science Ltd.