Three‐dimensional modeling of the Gulf of Lion's hydrodynamics (northwest Mediterranean) during January 1999 (MOOGLI3 Experiment) and late winter 1999: Western Mediterranean Intermediate Water's (WIW's) formation and its cascading over the shelf break

The Gulf of Lion's hydrodynamics are investigated with a numerical simulation of the 1998–1999 winter, performed with a three‐dimensional (3‐D) free‐surface model and real forcings. The model initial state derives from the large‐scale outputs of the MOM (1/8°) using a specific initialization method. The model results are validated with an oceanographic data set collected in the gulf during the MOOGLI3 cruise (11–21 January 1999). The modeled outputs agree well with the main hydrological and circulation patterns observed during MOOGLI3. The study focuses on a strong and peculiar event of dense water (Western Mediterranean Intermediate Water (WIW)) formation on the continental shelf and its cascading over the shelf break. This latter was detected by a steep temperature decrease in the time series of a mooring line in the nearby Lacaze‐Duthiers canyon which is well reproduced in the simulation. Modeled dense plumes appear during the MOOGLI3 period but more especially during late winter. Shapiro's theory of dense plume propagating on a sloping bottom is applied and provides information of the plume driving mechanisms. In both cases of plume studied, friction effects and Ekman drainage by the ambient current explain only a part of the plume motion. The complementary forcing is probably the steep local bathymetry irregularities. This 3‐D simulation permits also to evaluate the total amount of WIW formed during the 1998–1999 winter over the Gulf of Lion's shelf to 500 km 3 .