Ocean eddy energy budget and parameterization in the North Atlantic

Ke Zhao and David Philip Marshall, University of Oxford, Oxford, United Kingdom
The eddy energy budget and eddy-mean flow interaction is investigated in an eddy-resolving simulation of the North Atlantic using the thickness-weighted average framework. This focus on the eddy energy is motivated by the requirement of the recently developed GEOMETRIC and other eddy closures in which the eddy energy constrains the parameterized eddy stress tensor. Specifically in the GEOMETRIC parameterization, the depth-integrated eddy energy, including both kinetic and potential components, is the only dimensional parameter setting the magnitude of the eddy stress tensor and therefore must be parameterized in non-eddy permitting calculations. As found in previous observational and modelling studies, the diagnosed eddy energy is predominant in the vicinity of separated Gulf Stream and also adjacent to the western boundaries. The eddy energy tends to propagate westward, except in the core of the separated boundary current. The equations for the thickness-weighted average eddy kinetic and potential energy are derived and used construct an eddy energy cycle distinct from the traditional Lorenz energy diagram. The eddy energy source, eddy energy fluxes associated with advection and other processes, and the eddy energy sink are diagnosed. Preliminary results from our efforts to parameterize the depth-integrated eddy energy will also be discussed.