Large-scale, low-frequency barotropic circulation on continental margins

Abstract

Analytic solutions are obtained for forced, barotropic circulation at subinertial frequencies over a bilinear continental margin (shelf and slope) in situations where bottom friction is important. Three different alongshore forces are considered: wind-stress, offshore oceanic pressure gradients and offshore currents. Forcing functions are assumed to vary sinusoidally in time and in space alongshore. Steady models are found to perform adequately provided that the forcing functions do not move in the same direction as the free modes (continental shelf waves) propagate. Near resonance, when the alongshore velocity of the forcing approximates that of a free mode, the response is dominated by the mode. In the case of wind forcing, signals are trapped nearshore. If the shelf break occurs within this trapping length (as occurs near resonance) the shelf width becomes the effective trapping length. In this instance there can be significant horizontal shear in the alongshore velocity on the shelf near the shelf break. (A)