THE GENERATION OF TRANSVERSE FLOWS BY INTERNAL-FRICTION IN THE ST-LAWRENCE ESTUARY

Internal friction in combination with strong vertical variations of th e vertical shear of a current can set up a transverse circulation. The induced lateral flow field may be very important to the maintenance o f the steady density field. To date there has been little work aimed a t actually distinguishing this weak component of the flow in held data . We have compiled a set of velocity data for the St. Lawrence Estuary and we test for a relation between the second vertical derivative of the along-channel velocity and the lateral how. We find that the frict ionally driven circulation can only be identified when the second vert ical derivative of the along-channel current is very large, and that i n general the along-channel pressure gradient is at least as important as internal friction in generating cross-channel flow, in the St. Law rence Estuary. These results suggest that the simplest possible pictur e of the lateral circulation of the St. Lawrence Estuary, a single cel l with upwelling near the north shore and downwelling near the south s hore, is not tenable.