A Numerical Study of Stratified Tidal Rectification over Finite-Amplitude Banks. Part II: Georges Bank

Abstract

Tidal rectification over an idealized two-dimensional cross section of Georges Bank, which is a large, shallow, elongated submarine bank in the Gulf of Maine, is studied using a primitive equation coastal ocean circulation model. In the homogeneous case, the model predicts a topographically controlled residual circulation over Georges Bank, flowing northeastward as a strong jet with a maximum speed of about 16 cm s?1 along the northern flank and southwestward as a relatively weak and broad flow with a maximum speed of about 3 cm s?1 on the southern flank. As stratification is added, tidal rectification and tidal mixing intensify the along- and cross-isobath residual currents and create tidal fronts. During summer, the tidal fronts are located at the 40-m isobath on the northern flank and at the 50?60-m isobath on the southern flank, while during winter, the position of the tidal front remains fixed on the northern flank; however, it moves to the shelf break on the southern flank. The summer and winter maxima of the along-bank current are about 32 cm s?1 and 26 cm s?1 on the northern flank and 8 cm s?1 and 6 cm s?1 on the southern flank, respectively. The model results are in reasonable agreement with observations. The summertime intensification of the residual flow is mainly due to nonlinear interaction between the stratified tidal currents over the northern flank with the steep bottom topography there and to the baroclinic density gradient created in part by tidal mixing over the southern flank where the bottom slope is smaller.