Observation of Wavelike Motion of the Gaspe Current

Abstract

From current meter and satellite data, an unusual pattern of movement of the Gaspe Current was identified on two occasions in the summer of 1978. On the first occasion, the axis of the current moved offshore and the deep current reversed its normal seaward direction. In the satellite pictures, a wavelike structure of the Gaspe Current began to appear when the current was moving toward its normal nearshore position after a several-day excursion offshore. In a few days, it developed into a form resembling an overgrown wave, which eventually broke. The time span for the event is about 10 days. During the second episode, the appearance of a wavelike structure was also preceded by a shift in the position of the Gaspe Current, but the changes in the current direction and temperature were much less drastic than in the first event. Results of calculations based on Niiler and Mysak's model of barotropic instability for a coastal jet suggest that the wavelike motion may be triggered by the increased instability of the Gaspe Current when it is away from the coast, since the effect of the coast is stabilizing. The model predicts an e-folding time of 1 day, a wavelength of 52 km and a period of 4 days, which compare favorably with the observed wavelength of 60 km and period of 3?5 days.