The Origin of Low-Frequency Oscillations in the Southern Mid-Atlantic Bight

Abstract

Abstract Distinct offshore and upward phase propagation at periods of 12 and 24 days was previously observed in the horizontal flow field on the outer shelf in the southern Mid-Atlantic Bight during the Shelf Edge Exchange Processes Experiment in spring 1988. A linear, forced-wave model is invoked to explain the observed phase propagation. It is found that the observed phase propagation can exist when currents are in resonance with a vorticity source on the continental slope. It is essential that the thermohaline field be characterized by an upper-ocean stratification an the slope for resonance to occur. The phase difference near resonance is weakly dependent on the bottom frictional parameter and the alongshore length scale of forcing. Resonance is due to onshore propagation of topographic waves. It is suggested that low-frequency oscillations on the outer shelf in the Mid-Atlantic Bight in winter an associated with sources on the upper slope.