Laboratory observations of a gravity current on a sloping bottom: the generation of shelf waves

Abstract

A source of light water was started along the outside vertical wall of a cylindrical tank in uniform rotation. Like wall gravity currents studied previously, it had a nose which detrained eddies as it propagated. The gravity current then impinged upon a sloping bottom with the following effects: (i) the gravity current became more laminar; the detrainment of eddies at the nose and off the side of the current ceased; (ii) the gravity current became wider; (iii) the gravity current suddenly slowed and then continued to decelerate; (iv) when the gravity current was slower than the first-mode barotropic shelf wave, a shelf wave was radiated ahead of the gravity current; and (v) the deceleration was significantly greater than the deceleration of a gravity current next to a vertical wall. This is probably attributable to shelf-wave radiation drag, viscous effects and a finite energy source, although the relative importance of each remains an open question.