Calculating the ocean's residual overturning circulation using flow statistics

Pauluis et al.'s (2010) method for calculating the residual overturning circulation is implemented in the oceanic context and applied to an eddy resolving model. This method assumes that velocity and buoyancy fluctuations are normally-distributed random variables. It is found that, while the Gaussian assumption produces an overturning circulation which is qualitatively correct, there are significant regional errors. These errors indicate that the velocity and buoyancy fluctuations are regionally non-Gaussian. In particular, buoyancy perturbations are skewed and/or bimodal near meandering fronts. In addition, the velocity field is often significantly leptokurtic (i.e., “peaky”). To account for these departures from Gaussianity, the method is extended to more general probability distributions, with a focus on the “bi-Gaussian” distribution (sum of two Gaussians). The efficiency of the method and the implications of non-Gaussian eddy behavior are discussed.