3D turbulence field on the North-Western European Continental Shelf

Abstract

The 3-dimensional, non-linear, baroclinic, GHER mathematical model for the study of mesoscale motions (time scale of several hours to several days: tides, storm surges, ”) is described. Particular attention is paid to the turbulent closure based on an evolution equation for the turbulent kinetic energy and a parametric expression of the mixing length (k—model). Appropriate boundary conditions and numerical techniques (mode-splitting, implicity, σ-coordinate system, advection scheme) are described. The model is applied to the simulation of the M₂ tide on the North-Western European Continental Shelf not only without wind but also in typical winter and summer conditions. Large spatial variations of the turbulent kinetic energy appear as a result of the variations of depth and tidal activity around the shelf. These variations are clearly related to the different turbulence regimes observed in summer, with frontal structures separating well-mixed waters from stratified ones. The structure and evolution of the vertical profiles of turbulence variables are described and explained in barotropic and baroclinic conditions, under different wind forcings. The evolution of these profiles at the M₂ tide frequency largely depends on the eccentricity of the tidal ellipse.