Anisotropy of Ocean Eddies

This paper examines the anisotropy of ocean eddies in an eddy-resolving (1/12-degree) global ocean model. The variability of the horizontal velocity fields are analyzed using the variance ellipse framework, which characterizes the geometry of the variability in terms of the eddy kinetic energy, anisotropy and orientation. It is found that the eddy anisotropy has significant vertical structure and is strongest close to the ocean bottom, where the anisotropy tends to be oriented with the underlying isobath. The strong anisotropic bottom signal is almost entirely contained in the barotropic variability. Upper-ocean variability is predominantly baroclinic and less sensitive to the underlying bathymetry. This finding offers guidance for introducing a parameterization based on the underlying bathymetry to operate on the barotropic flow, to better account for barotropic variability unresolved in coarse-resolution ocean models.