The effects of rotation on localized buoyancy driven convection

A circular, surface-mounted salt-water-source issues fluid into a homogeneous ambient fluid in order to simulate a natural local buoyancy source. DPIV images are taken to study the resulting flow with or without background rotation. Side view images show a stable two layer flow when no background rotation is present. Density data taken beneath the source show the significance of the buoyancy time scale defined by the water column height divided by a characteristic fall velocity. Once background rotation is added, a frontal instability immediately forms on the outflowing gravity current. Top view DPIV images show that this instability results in uniformly spaced vortices around the source. Each vortex is shown to be a Taylor-like column moving under the influence of the induced velocity fields of its neighbors. When a flat bottom is used, the vortices are observed to wander about freely in the tank. However, when a sloping bottom is present, the vortices are trapped around the source. Power law dependencies of the length and vorticity scales of the instability vortices on the dimensionless parameters are presented. The vortices are observed to control the ambient inflow beneath the source and are shown to reduce the mixing. The mixing is shown to scale with the Rossby number to the 1/6 power, which indicates that the steady state density anomaly is weakly dependent on the background rotation.