Dynamics of a buoyancy-driven coastal jet: The Gaspe Current

A primitive equation ocean model is applied to the process study of the Gas pe Current and cyclonic circulation over the northwestern Gulf of St. Lawre nce (NWG). The model is driven by river discharge and barotropic boundary f lows. Two types of model domains are used: an idealized basin with a flat b ottom and piecewise coastline, and a realistic basin with model-resolved NW G bathymetry. The model domains are initially filled with horizontally unif orm but vertically stratified waters. The river discharge is expressed in t erms of lower salinity and a weak barotropic inflow in the upper waters at the estuary head. The early developments of the estuarine plume and coastal current system dr iven by the river discharge are qualitatively similar in both basins. After a short-period adjustment, a buoyant plume is developed near the estuary m outh, with a surface-intensified coastal current advecting the estuarine wa ter seaward in the direction of Kelvin wave propagation. The coastal curren t initially follows the coastline closely but later becomes unstable with b ackward-breaking waves developed along the outer edge of the current. The k inetic energy analysis reveals that the plume-current system is baroclinica lly unstable with the transient motions resulting primarily from the mean a vailable potential energy. With the river discharge at the head as the only driving force, the offshor e front of the estuarine plume expands continuously seaward, leading to a l arge-scale anticyclonic circulation over the NWG. The addition of a barotro pic westward jet along the Quebec shore, however, is able to restrain the s eaward expansion of the offshore front of the plume, and therefore form a l arge-scale cyclonic motion over this region.