Inertial Boundary Layer with a Velocity Front: HOW the Bottom Slope Controls the Western Boundary Current Path

Abstract

The western boundary current of the subtropical gyre flows on the upper continental slope and is controlled by the bottom topography; however, our theoretical understanding of how the path of the boundary current is determined is insufficient. For example, in the conventional inertial boundary-layer theory that uses an impenetrable coastal boundary, the path of the boundary current (position of maximum velocity) is always on the externally given boundary. In the present study, a new mechanism is proposed of the path determination based on an extended inertial boundary-layer theory. Two regions are assumed: an offshore active region filled with gyre water and an inshore stagnant region where there is no motion. These regions are divided by a free streamline (a velocity front), across which the pressure is continuous but the velocity may be discontinuous. The restriction of continuous pressure determines the frontal position or the path of the boundary current. The stagnant region controls the path through the effect of the bottom slope. The results of an improved model show some qualitative agreement with observed boundary currents.