Experiments on turbulent convection over a rotating continental shelf–slope

Abstract

A series of Southern Hemisphere experiments have been performed to study turbulent convection on a continental shelf–slope placed in a large rotating tank filled with fresh water. Dense salt water was uniformly released at the fluid surface above the shelf. The resulting negatively buoyant bottom flow travelled over the shelf and then downslope. The non-dimensional reduced gravity of the dense downslope flow was found to scale as$G'\,{=}\,g'h^{4/3}/(B_{0}^{2/3}W)$for a fixed slope angle, whereB0the buoyancy flux at the surface,g′ the reduced gravity of the bottom flow,hthe water depth above the shelf andWthe width of the dense water source. Under rotation, a bottom Ekman layer, with superimposed roll waves, propagated down the slope and towards the left sidewall when looking down the slope. As the modified natural Rossby numberPdecreased, whereP= (B0/f3h2)1/2W/handfis the Coriolis parameter, the appearance of the bottom layer had four different forms: laminar flow, the continuous formation of waves, the periodic release of wave groups, and the periodic generation of eddies. Vortices generated on the surface were cyclonic, suggesting, but not proving, that eddies in the dense bottom layer as originally formed were anticyclonic.With a canyon cut from the middle of the shelf to the bottom of the slope,G′ values measured in dense flows to the left of the canyon, were significantly reduced. The canyon channelled a large amount of dense fluid with a buoyancy considerably larger than that of dense flows on the slope. However, the flow regime criteria remained basically unchanged with eddies and downslope Ekman layer being able to partially cross the canyon.