Lognormal turbulence dissipation in global ocean models

Data from turbulent numerical simulations of the global ocean demonstrate that the dissipation of kinetic energy obeys a nearly lognormal distribution at surprisingly large horizontal scales. As the horizontal scales of resolved turbulence are larger than the ocean is deep, the KolmogorovYaglom theory for intermittency in 3D homogeneous, isotropic turbulence cannot apply: instead the downscale potential enstrophy cascade of quasi-geostrophic turbulence should. Yet, energy dissipation obeys approximate lognormality–robustly across depths, seasons, regions, and subgrid schemes. The distribution parameters, skewness and kurtosis, show small systematic departures from lognormality with depth and subgrid friction schemes. Lognormality suggests that a few high dissipation locations dominate the integrated energy and enstrophy budgets, which challenges the representativeness of both sparse observations and simplified models.