Application of a transient reduced gravity plume model to the Denmark Strait Overflow

Abstract

A hydrostatic, reduced gravity, two‐dimensional primitive equation numerical model for the simulation of transient bottom arrested gravity plumes was developed by adopting an algorithm from a wadden sea model (a model that simulates the wetting and drying of mud flats, sand banks, etc.) with a movable lateral boundary. The vertically integrated nonlinear rotational model accounts for the dissipation of momentum due to bottom friction and for the entrainment of water mass properties from a spatially structured but stagnant ambient water body. It predicts the temporal and spatial evolution of the flow field and the water mass modification within a gravity plume that descends on an arbitrary topography. Previous model investigations considered a laterally integrated streamtube, whereas our model resolves the plume horizontally. In the streamtube approach it was assumed that the plume descends in a stationary, almost geostrophic balance modified only by bottom drag and entrainment. The results of this model demonstrate that this balance may be disturbed whenever the plume encounters topographic disturbances, which, for the initial intruding phase in particular, accounts for its highly transient character. The model results are in good agreement with theoretical and laboratory investigations and with observations, as is demonstrated by some basic test experiments. An application to the overflow of dense water through the Denmark Strait is presented.