119 Filtering the Ocean: New Insight into the Baroclinic Instability

Tuesday, 27 June 2017
Salon A-E (Marriott Portland Downtown Waterfront)
Mahmoud M Sadek, University of Rochester, Rochester, NY; and H. Aluie, G. K. Vallis, and M. W. Hecht

The ocean is mechanically driven by wind and buoyancy at the surface which produce sloping isopycnals with a reservoir of available potential energy (APE). APE can be converted to kinetic energy via baroclinic instability, which is believed to drive mesoscale eddies. The widespread belief that mesoscale eddies are generated through baroclinic instability is based on apparent accord between observations and linear stability analysis, using idealized models. In reality, the ocean is never under such idealized conditions. At present, aside from crude order of magnitude estimates, we still lack direct measurements evidencing the extent to which this instability is responsible for eddy generation at various locations in the ocean.

To this end, we implement a coarse-graining framework, recently developed to study flow on a sphere, to directly analyze the conversion between potential (PE) and kinetic energy (KE) as a function of scale and geographic location. We apply our method to strongly eddying high-resolution simulations in the North Atlantic and in the Southern Ocean, using POP and ECCO data. In this fully nonlinear realistic ocean setting, we determine (1) the scales and rate at which PE is stored via Ekman pumping and (2) the scales and rate at which PE released back to drive oceanic flow. We find that while the strongest PE to KE conversion occurs at a scale that is correlated with the Rossby deformation scale, there is significant PE to KE conversion over an entire range of oceanic scales.
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