Hydraulically Drained Flows in Rotating Basins. Part II: Steady Flow

Abstract

The slow, horizontal circulation in a deep, hydraulically drained basin is discussed within the context of reduced-gravity dynamics. The basin may have large topographic variations and is fed from above or from the sides by mass sources. Dissipation is provided by bottom friction. To the order of the appromixations made (weak forcing and dissipation), the nonlinear hydraulic control is found to influence only the mean level of the interface separating upper and lower layers, and not the horizontal circulation. For the case of forcing from above the interior basin flow is anticyclonic about closed geostrophic contours and feeds into diffusive boundary layers leading to the draining strait and sill. With sidewall forcing, the interior is motionless and flow is channeled directly to the strait in boundary layers. The latter may circle the basin cyclonically or anticyclonically depending on the source distribution, and a circulation integral is shown to predict the sense of the overall swirl velocity and the presence of eastern and western boundary currents. Modifications caused by the presence of open geostrophic contours or horizontal friction are commented upon. The model is used to predict pathways for deep flow entering the Norwegian Sea from the Greenland Sea and escaping through the Faroe?Shetland Channel. Comparison with the few existing observations are made.