The TRR 181 seminar is held by Dr. Ian Grooms (University of Colorado, Boulder) on April 7, 4 pm.

Offline diagnostics of eddy energetics with spatial filtering in an idealized model

Abstract

Abstract: Energy exchanges between large-scale ocean currents and mesoscale eddies play an important role in setting the large-scale ocean circulation but are not fully captured in models. To better understand and quantify the ocean energy cycle, we apply along-isopycnal spatial filtering to output from an isopycnal 1/32 degree primitive equation model with idealized Atlantic and Southern Ocean geometry and topography. Spatial filtering is accomplished using the diffusion-based filter framework of Grooms et al. (JAMES 2021), which is briefly reviewed. Using this filter, we diagnose the energy cycle in two frameworks: (1) a non-thickness-weighted framework, resulting in a Lorenz-like energy cycle, and (2) a thickness-weighted framework, resulting in the Bleck energy cycle. This paper shows that (2) is the correct framework for studying energy pathways when an isopycnal average is used. Next, we investigate the Bleck cycle as a function of filter scale. Baroclinic conversion generates mesoscale eddy kinetic energy over a wide range of scales, and peaks near the deformation scale at high latitudes, but below the deformation scale at low latitudes. Away from topography, an inverse cascade transfers energy from the mesoscales to larger scales. The upscale energy transfer peaks near the energy-containing scale at high latitudes, but below the deformation scale at low latitudes. Regions downstream of topography are characterized by a downscale kinetic energy transfer, in which mesoscale eddies are generated through barotropic instability.