A Three-Dimensional Numerical Study of Deep-Water Formation in the Northwestern Mediterranean Sea

Abstract

Deep-water formation (DWF) in the northwestern Mediterranean Sea and the subsequent horizontal circulation are investigated in a rectangular basin with a three-dimensional primitive equation model. The basin is forced by constant climatological heat and salt fluxes. Convective motion is parameterized by a simple nonpenetrative convective adjustment process plus Richardson number?dependent vertical eddy viscosity and diffusivity. A homogeneous column of dense water is progressively formed in the forcing area. Meanders of 40-km wavelength develop at the periphery of the column. These features agree with observations. Energy studies show that the meanders are generated mainly through a baroclinic instability process. These meanders, and the associated cells of vertical motion, contribute to the process of DWF. They generate vertical advection, while the associated horizontal advection tends to restratify the surface water of the column, and thus to inhibit very deep convection. Just before the end of the forcing period, 80-km meanders appear, which create advection strong enough to erase the column within two weeks. The associated horizontal cyclonic circulation is of the same order of magnitude as that estimated from observations.