Wind-driven inertial currents in the Magdalen Shallows, Gulf of St. Lawrence.

Abstract

Power spectrum analyses of the residual current components from the Magdalen Shallows (autumn 1970) gave a prominent peak at the inertial frequency. Bandpass filtering showed that the inertial oscillations occurred in bursts of 2-3 days duration and with irregular intervals between bursts. The transient nature of the above behaviour was consistent with the pulselike nature of the wind stress and a convincing linear correlation was found between the magnitude of the wind stress and the rms residual current. Using a simple slab model with a lin ear drag law, it was found that the transient response to a typical wind stress pulse was also pulselike, with a relatively small phase lag. The magnitude of the reponse was found to be a sensitive function of the duration of the wind stress pulse. Comparison of the theory with the experimental results indicates that the simple slab model is a good approximation. The results suggest that, on average, about 50% of the residual current speed was due to the local wind. (A)