An ensemble-based eddy and spectral analysis, with application to the Gulf Stream

The `eddying' ocean, recognized for several decades, has been the focus of much observational and theoretical research.  We here describe a generalization for the analysis of eddy energy, based in the use of ensembles, that  addresses two key related issues: the definition of an `eddy' and the general computation of energy spectra. An ensemble identifies eddies as the unpredictable component of the flow, and permits the scale decomposition of their energy in inhomogeneous and non-stationary settings. It also avoids the `tapering' or `windowing' of the data required by traditional approaches. We apply the analysis to a mesoscale resolving  (1/12 degree) ensemble of the separated North Atlantic Gulf Stream. Our results show that the eddies are consistent with the theoretical predictions of quasi-geostrophy both at the surface and ocean interior.