Subinertial Response of a Density-Driven Eastern Boundary Poleward Current to Wind Forcing

Abstract

A high-resolution primitive equation numerical model is used to generate a poleward flow along a meridionally oriented eastern boundary slope/shelf system by imposing an along-coast density gradient as the forcing mechanism. Wind forcing is applied to the resulting quasi-steady current system, and the subinertial response is analyzed. Parallel experiments with no slope-poleward flow are conducted for comparison. Moderately strong upwelling- and downwelling-favorable, week-to-month-scale wind events modify the poleward flow but do not significantly change the density-driven current structure at the slope. The alongshore transport within the slope region is reduced by 0.2?0.3 Sv (from 1.2 Sv, where Sv ≡ 106 m3 s?1), under the influence of either downwelling or upwelling winds. Independent of the wind direction, the density-driven poleward flow always remains surface intensified. Wind-driven shelf currents develop with a considerable degree of independence from the slope-poleward circulation. On the shelf, the density field is modified by cross-shelf buoyancy advection within the boundary layers and by strong vertical mixing. The presence of the poleward flow over the slope constitutes an important factor in the behavior of the bottom boundary layer at the shelf break and for the patterns of cross-slope circulation.