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Center for Nonlinear Studies |
This study characterizes the dynamics of a turbulent gravity current flowing down a uniform slope in a rotating media. These dense overflows are of particular interest in oceanography since it is an important mechanism in renewing deep water as part of the global thermohaline convective cycle. The large Coriolis turntable (LEGI) is used to study at the laboratory scale, a gravity current in similarity with the oceanic scales. The propagation of such currents is strongly influenced by rotation, bottom topography and mixing with the ambient fluid, that induce unstable dynamics. Interactions between the gravity current and the ambient fluid, due to entrainment and detrainment phenomena, control the stabilization depth of the main current along the coast, as well as its velocity and density. Scaling laws are derived, describing the main properties of the flow along the slope, where the buoyancy flux is conserved. This highly turbulent regime leads to a self-similar behaviour of the main flow. Laboratory experiments are used to determine the rate of mixing arising both from small-scale turbulence with entrainment of the ambient fluid and detrainment phenomena, and geostrophic turbulence with generation of large scale instabilities. The intensity of horizontal turbulent stress is closely related to the formation and displacement of large cyclonic vortices also visible in oceanic flows.
Host: Bob Ecke, T-CNLS