The effects of double-diffusion on a baroclinic vortex

Abstract

Laboratory experiments were performed to study the combined effects of double-diffusion and rotation on an oceanic intrusion. Intrusions are driven across density-compensated fronts by the divergence of the double-diffusive buoyancy flux. The increased momentum transport across a double-diffusive interface, however, acts to oppose the action of the buoyancy flux. Turbulent double-diffusive Ekman layers could be a means of redistributing momentum. A model of an intrusion was made by injecting salt or sugar solution at the surface of a denser layer of sugar or salt solution in a rotating tank to form a baroclinic vortex. The size and shape of the vortex and the velocity structure of the intrusion were measured as functions of time. The double-diffusive vortex spread more quickly and had slower azimuthal velocities than a non-double-diffusive one. This effect increased as the density ratio approached unity. These results indicate that momentum transport across a double-diffusive interface is larger than that across a non-double-diffusive one; thus, the parameterization of friction in an intrusion model should be considered carefully.