3D TURBULENCE FIELD ON THE NORTH-WESTERN EUROPEAN CONTINENTAL-SHELF

The 3-dimensional, non-linear, baroclinic, GHER mathematical model for the study of mesoscale motions (time scale of several hours to severa l days: tides, storm surges, ...) is described. Particular attention i s paid to the turbulent closure based on an evolution equation for the turbulent kinetic energy and a parametric expression of the mixing le ngth (k-model). Appropriate boundary conditions and numerical techniqu es (mode-splitting, implicity, sigma-coordinate system, advection sche me) are described. The model is applied to the simulation of the M2 ti de on the North-Western European Continental Shelf not only without wi nd but also in typical winter and summer conditions. Large spatial var iations of the turbulent kinetic energy appear as a result of the vari ations of depth and tidal activity around the shelf. These variations are clearly related to the different turbulence regimes observed in su mmer, with frontal structures separating well-mixed waters from strati fied ones. The structure and evolution of the vertical profiles of tur bulence variables are described and explained in barotropic and barocl inic conditions, under different wind forcings. The evolution of these profiles at the M2 tide frequency largely depends on the eccentricity of the tidal ellipse.