The latitudinal dependence of the oceanic barotropic eddy kinetic energy and macroturbulence energy transport

Geostrophic turbulence theory predicted already a few decades ago an inverse energy cascade in the barotropic mode, yet there has been limited evidence for it in the ocean. In this study, the latitudinal behavior of the oceanic barotropic energy balance and macroturbulent scales is studied using the ECCO2 (Estimating the Circulation and Climate of the Ocean) state estimate, which synthesizes satellite data and in situ measurements with a high-resolution general circulation model containing realistic bathymetry and wind forcing. It is found that inverse energy cascade occurs at high latitudes, as eddy-eddy interactions spread the conversion of eddy kinetic energy from the baroclinic to the barotropic mode, both upscale and downscale. At these latitudes, the conversion scale of baroclinic eddy kinetic energy and the energy-containing scale follow the most unstable and Rhines scales, respectively. Even though an inverse energy cascade occurs at high latitudes, the energy spectrum follows a steeper slope than the -5/3 slope. Different than classic arguments, the Rossby deformation radius does not follow the baroclinic conversion and most unstable scales.