Application of Turbulence Energy Models to the Computation of Tidal Currents and Mixing Intensities in Shelf Edge Regions

Abstract

The major steps in the formulation of a three-dimensional shelf edge model using a sigma coordinate system in the vertical are briefly described. Vertical diffusion of momentum is parameterized using a range of turbulence closure models, and results are compared with earlier calculations using a simple flow-related viscosity. The influence of the magnitude of horizontal eddy viscosity upon spatial variability at the shelf edge is examined. The model is applied to the calculation of M2 and O1 tidal elevations and currents in the shelf edge region off Scotland (the Hebrides shelf), and comparisons are made with data collected in the region. Computed M2 tidal elevations and currents are shown to be in adequate agreement with observations, with no significant differences between tidal profiles computed with the turbulence energy models or the earlier calculations using a simple viscosity model. The magnitude of the horizontal eddy viscosity does not appear to affect this component of the tide. Tidal currents in deep water are not influenced by the presence of a specified (diagnostic) temperature profile, although this does influence the profile in some shallow sea regions. Computed O1 tidal currents in the shelf edge region exhibit local spatial variability and are significantly influenced by the magnitude of horizontal viscosity and grid resolution.