Influence of diurnal heating on stratification and residual circulation of Georges Bank

Abstract

The influence of the diurnal heat flux on summer stratification and residual circulation over Georges Bank was examined using a three-dimensional primitive equation numerical circulation model. For a given spatially uniform and time-varying heat flux the model results show that the surface water is heated much faster on the southern flank than on the northern flank and much faster in the stratified region than in the mixed region. Heating significantly strengthens the tidal mixing front and intensifies the frontward convergence near the surface. As seasonal stratification develops, the location of the tidal mixing front gradually shifts on bank on the southern flank, while remaining almost unchanged on the northern flank. Response of the tidal currents to the diurnal variation in the heat flux varies across Georges Bank. It changes periodically with tidal cycles on the southern flank but is locked to the phase of the eastward tidal current on the northern flank. This phase-lock feature directly contributes to the intensification of the along-bank residual current jet on the northern flank. Diagnostic analysis suggests that this intensification is mainly caused by the heat-enhanced, cross-bank momentum flux. Model-computed variations of near-surface temperature and residual currents are in good agreement with satellite-derived sea surface temperature data and drifter measurements. Copyright 2003 by the American Geophysical Union.