Mixing in downslope flows in the ocean ‐ plumes versus gravity currents

Abstract

The nature of downslope flows into stratified environments as revealed by laboratory experiments is described, and the results are then applied to interpret particular downslope flows into the ocean. In the laboratory, non‐rotating downslope flows can be divided into two main types: detraining gravity currents over sufficiently gentle slopes, where the buoyancy force of the dense downflow is mainly balanced by bottom drag, and entraining plumes over sufficiently steep slopes, where the buoyancy force is balanced by vigorous entrainment of environmental fluid from above. This mixing character of the flow is determined by the bottom slope, the drag coefficient and the buoyancy number B = QN3/G2, where Q and G are the volume flux and buoyancy of the down‐flow and N is the buoyancy frequency of the environment. These experiments may be applied to situations in the ocean where the flow is in approximate geostrophic balance with its transverse pressure gradient, and the parameters are applied to the flow path on the slope. Examples are provided for a number of downslope flows in various locations, including the Red Sea outflow, the Mediterranean outflow into the Black Sea and the Atlantic, the Denmark Strait overflow and the outflow from the Ross Sea.