Submesoscale Topographic Wakes

The interaction of oceanic boundary currents with topography can induce high-vorticity bottom boundary layers that on separation and subsequent rollup through barotropic-centrifugal instabilities can lead to a significant input of vorticity into the ocean interior. Recent studies show that the strength of this vorticity is proportional to the speed of the boundary current and local slope of the topography. The separating bottom shear layers have horizontal scales of O(100m) and vortex Rossby numbers > 1, that are typically associated with submesoscale currents in the ocean. We generalize a recently proposed mechanism for vortex generatio into one involving the potential vorticity of the separated shear layers and its dependence on latitude and local stratification. Employing idealized configurations of uniform stratified flow past seamounts and realistic high-resolution ROMS computations (in the 250-500 m range) in the Southwest Equatorial Pacific in and around the Solomon Sea, we elucidate the barotropic-centrifugal instability process that generates submesoscale coherent vortices (SCVs) through these mechanisms. In particular we show that near-equatorial SCVs can have larger vortex Rossby numbers (~20) that are also accompanied by significant interior dissipation and mixing.