Lagrangian Dispersion Over a Ridge in a Laboratory ACC Driven by Wind and Buoyancy Forcing

The Lagrangian motion of neutrally-buoyant particles is observed in a laboratory channel model of the Antarctic Circumpolar Current (ACC). The competing mechanisms of buoyancy and wind forcing present in the ACC are simulated in a rotating annulus of fluid by imposing a radial temperature gradient across the annulus gap, while applying mechanical forcing at the surface through the differential rotation of a rigid lid in contact with a surface layer of oil. A radially-sloping bottom creates a fluid depth gradient that mimics the planetary β-effect. Simple topography is present in the form of five regularly spaced meridional ridges. By varying the strength of wind and thermal forcing on the fluid, several regimes of flow are produced. Analysis of Lagrangian trajectories within the fluid shows marked difference in particle dispersion, transport, and wave activity depending on the forcing regime. Interaction with topography is analyzed and the varying effects of wind and stratification are shown to affect the tendency of particles to follow isobaths and the overall cross-ridge transport.