A global diagnosis of Eddy Potential Energy budget in an eddy-permitting ocean model

By closing the EPE budget, we are able to properly investigate the role of diabatic processes in modulating mesoscale energetics in the context of other processes driving eddy-mean flow interactions. A Helmholtz decomposition of the eddy heat flux field into divergent and rotational components is applied to estimate the baroclinic conversion from mean to eddy potential energy.

In doing so, an approximate two- way balance between the "divergent" baroclinic conversion and upgradient vertical eddy heat fluxes in the ocean interior is revealed, in accordance with baroclinic instability and the relaxation of isopycnal slopes. However, in the mixed layer, the EPE budget is greatly modulated by diabatic mixing, with air-sea interactions and interior diffusion playing comparable roles. Globally, this accounts for similar to 60% of EPE converted to EKE (eddy kinetic energy), with the remainder being dissipated by air-sea interactions and interior mixing.