THE ORIGIN OF LOW-FREQUENCY OSCILLATIONS IN THE SOUTHERN MID-ATLANTICBIGHT

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