Robert Scott
Institute for Geophysics, University of Texas at Austin

Altimeter Data Reveals and Anisotropic Inverse Cascade in the Surface Geostrophic Flow of the World Ocean

Seven years of sea-surface height observations from multiple satellites are used to analyze the kinetic energy spectrum and cascades of mesoscale oceanic turbulence. We find a ubiquitous inverse energy cascade, with source of kinetic energy close to the deformation scale (within a factor of two). Analyzing the 2d spectrum revealed the first evidence of a ubiquitous preference for zonally elongated modes. Diagnosing the 2d spectral energy transfer reveals the kinetic energy forcing as a function of kx and ky, and the nonlinear interactions associated with the inverse energy cascade. We found the forcing to preferentially drive meridionally elongated eddies, the signature of potential energy release via baroclinic instability due to zonal mean flows. A previously unobserved nonlinear cascade redistributes kinetic energy preferentially to larger scales, and toward zonally elongated eddies. The anisotropy in the cascade is believed to result from the rotation and curvature of the Earth. Still unexplained, the cascade is less effective at higher latitudes.