The Multiscale Nature of Potential to Kinetic Energy Conversion in the Ocean

Oceanic mesoscales play a crucial role in the ocean’s energy cycle. The widespread belief is that mesoscale eddies are driven by the conversion of available potential energy (APE) into kinetic energy (KE) through the baroclinic instability. Such a belief is based on apparent accord between observations and linear stability analysis, using idealized models. 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 as well as the associated characteristic length-scales.

To this end, we implement a coarse-graining framework to directly measure the conversion between (PE) and (KE) as a function of scale and geographic location in the real ocean. We have recently also shown how such a framework can be used to extract the spectrum.

Accordingly, these diagnostics are applied to the Southern Ocean using data from eddy resolving simulations and altimetry.

We determine (i) the scales and the rate at which PE is stored via Ekman pumping, (ii) the scales and the rate at which PE is released back to drive oceanic flow via baroclinic conversion and (iii) the most energetic eddy length-scale. We also analyze the seasonality of these processes and show how they correlate with the KE content at various scales.