THE GULF STREAM AS AN INERTIAL BOUNDARY LAYER

Abstract

Notable advances have been made in our understanding of the ocean circulations in the past few years. The general westward intensification of the wind-driven circulation was shown by Stommel1 to be a consequence of the variation of the vertical component of the earth’s angular velocity. Owing to a tendency toward conservation of absolute vertical vorticity, a fluid column moving poleward in the Northern Hemisphere acquires a relative clockwise spin, and a fluid column moving Equatorward a counterclockwise spin. As a result, the clockwise circulation of the ocean is intensified in the west and reduced in the east. Using actual wind stresses, Munk2 was able to account for the principal features of the mean circulation of the open ocean. The detailed structure of the western current remained, however, essentially unexplained. The eddy-frictional mechanism employed by Munk to provide the necessary energy dissipation for the entire ocean was inapplicable to the individual boundary current. In order to account for the observed width of the current, Munk was forced to postulate an eddy viscosity so large that the eddy sizes were themselves comparable to the width. Such eddies are observed in the meanderings of the boundary current after it leaves the continental slope but are then cut-off branches of the current itself and therefore can have nothing to do with its structure.