SEMINAR: OI Seminar Series - Jessica Benthuysen

The Leeuwin Current: The Role of Mixing and Advection in Topographic Trapping and Shelfbreak Intensification of a Density-Driven Flow Jessica Benthuysen CSIRO Marine and Atmospheric Research, Centre for Australian Weather and Climate Research

The Leeuwin Current is a poleward eastern boundary current that is shelfbreak intensified. A suite of numerical experiments is used to investigate the role of buoyancy forcing of this current over shelf-slope topography. The buoyancy forcing is composed of a meridional density gradient distributed over an upper layer depth, which balances a zonal geostrophic flow. The intersection of this upper layer with the slope supports a poleward current by topographic trapping of Rossby waves. The position of the upper layer's intersection sets the offshore width of the current. Key processes, including mixing and advection, modify the current's speed, transport, and spatial structure. Vertical diffusion thickens the upper layer, strengthening the poleward current. Horizontal viscosity modifies the current width over which the zonal flow converges and hence controls the jet speed. Poleward density advection forms a cross-shelf density front, intensifying the poleward flow near the surface. Offshore advection by bottom frictional flow can contribute to the jet’s frontal position near the shelf break. The simulations also reveal cases in which an equatorward flow exists at depth, similar to a Leeuwin Undercurrent.