Anisotropy of the kinetic energy cascade measured with altimeter data for the World Ocean

The dynamical origin of the apparently ubiquitous jets seen in observations and realistic model simulations of the World Ocean remains unclear. We address the possibility of a nonlinear origin by directly measuring the turbulent kinetic energy cascade. Six years of sea-surface height observations from multiple satellites reveal a ubiquitous preference for current anomalies stretched in the zonal direction. The two-dimensional nonlinear spectral transfer revealed that forcing preferentially drives meridionally elongated flow, the signature of potential energy release via baroclinic instability. A nonlinear cascade redistributes energy preferentially to larger scales, and toward zonally elongated flow, direct observational evidence of the beta-effect on the inverse cascade anisotropy. Still unexplained, the cascade was found to be less effective at higher latitudes.