Topographic effects on the dynamics of gravity currents in a rotating system

The effect of a sloping bottom on the stability and evolution of buoyant currents in a rotating system is studied in the laboratory. Experiments varying the bottom inclination and the density contrast between buoyant and ambient fluid were carried out. Two different techniques were used to generate the currents: gravitational collapse and continuous injection of fluid. Currents generated by gravitational collapse develop meanders and when the bottom inclination is large the meanders grow and form eddies. In contrast, when the inclination is small the growth of the meanders is inhibited. Currents generated by continuous injection widen smoothly up to a point where the fluid beneath them is sufficiently thick so that the bottom-frictional influence is negligible, and the currents start to develop meanders. In both cases the presence of the inclined bottom stabilises the current, most probably because of friction. A theoretical model of geostrophic adjustment of a buoyant wedge is derived and analysed, showing that in the absence of friction and diffusion the buoyant fluid spreads almost one deformation radius, converting into kinetic energy less than one-third of the potential energy released. Comparisons between the experimental and theoretical profiles of velocity and potential vorticity show large differences, thus friction, absent in the model, might be a determining factor.