Zonal Jets over Topography on a Beta-Plane, with Applications to the Kuroshio Extension over the Shatsky Rise

Abstract

Abstract The response of an initially zonal barotropic or baroclinic jet to an isolated seamount or a meridional ridge is investigated here using a three-dimensional primitive equation model with a free surface. An eastward jet with an axial speed U and a half-width Ly over a β plane is supercritical if the Froude/Rossby number (U/βL2y) is greater than about 0.25, and subcritical otherwise. A westward jet with a negative U and hence a negative U/βL2y is always supercritical. Following this definition proposed by Armi, an obstacle renders barotropic zonal jets subcritical or less supercritical especially to the west of the obstacle. For an initially supercritical eastward jet, a significant obstacle projects its influence upstream through a migrating “hydraulic jump,” broadening and weakening the incoming jet. For subcritical and westward jets, the westward influence is achieved by the propagation of long Rossby waves. In the barotropic regime, the westward influence increases with |U/βL2y| and the height ...