A NUMERICAL STUDY OF STRATIFIED TIDAL RECTIFICATION OVER FINITE-AMPLITUDE BANKS .1. SYMMETRICAL BANKS

Tidal rectification over a two-dimensional. finite-amplitude symmetric al bank is studied using the Blumberg and Mellor primitive equation co astal ocean circulation model (ECOM-si). In the homogeneous case, the nonlinear interaction of tidal currents with the variable bottom topog raphy generates an along-isobath residual circulation over the bank, w hich tends to increase as either the slope or height of the bank is in creased. In the stratified case, internal waves at tidal and higher fr equencies are generated over the sloping sides of the bank, Tidal mixi ng occurs in the bottom boundary layer, leading to horizontal tidal mi xing fronts. The resulting stratified tidal rectification associated w ith the tidal mixing front, the generation of internal tides, and the modification of internal friction due to stratification leads to a sub surface intensification of the along-isobath residual current at the f ront and at the top of the bottom mixed layer over the slope, and a cr oss-bank double cell circulation pattern centered at the front near th e shelf break. Model results for tidal mixing are in reasonable agreem ent with a simple energy argument in which the thickness of the tidal mixed layer is proportional to the magnitude of the tidal current and inversely to stratification.