Similarities and Differences Between Eddy diffusivities of Thickness and PV

There are continuing debates on the use of eddy diffusivity of thickness or potential vorticity (PV) in parameterizing meso-scale eddy in coarse-resolution models. It has been shown that the ocean simulations with parameterized thickness diffusivity differ from those with parameterized PV diffusivity. However, the comparison of thickness-diffusivity and PV-diffusivity themselves based on eddy-resolving simulations gives contrasting results: some show similar thickness- and PV-diffusivities, while other show different diffusivities, possibly due to the various methods adopted in the definition and calculation of the eddy diffusivities. In this research we compare the similarities and differences between eddy diffusivity of thickness and that of PV by carefully calculating the two isopycnal eddy-diffusivities based on three global eddy-resolving simulations or reanalysis (LICOM2, HYCOM, and MITGCM). The calculation of eddy diffusivity is based on the least-square estimation between the divergence of eddy fluxes and the Laplacian of the mean fields of thickness or PV, so as to remove the effect of rotational part of eddy flux. The comparison over the Southern Ocean shows that the amplitude and 3-D pattern of thickness diffusivity is close to that of PV diffusivity with slight differences between them. The results show enhanced eddy diffusivity of both thickness and PV associated with the ACC. The causes of the similarities and differences will be analyzed in the presentation, and we also will show the difference in the estimate of eddy diffusivity associated with the scale or the target resolution of the coarse-resolution model.