Geographical distribution and anisotropy of the inverse kinetic energy cascade, and its role in the eddy equilibrium processes

Abstract

The geographic character of the inverse cascade is analyzed based on the spectral kinetic energy flux calculated in the global ocean, using sea surface height (SSH) data from satellites, reanalysis data, and model outputs. It is shown that the strongest inverse cascade occurs mostly in high-energy eastward-flowing currents, such as the Antarctic Circumpolar Current (ACC), the Kuroshio Extension, and the Gulf Stream, which matches the global distribution pattern of the eddy kinetic energy (EKE). Hence, the eddy scales predicted by the local linear baroclinic instability L-bci and from the altimeter observation L-eddy are mapped out and compared with the energy injection scale L-inj and the arrest-start scale Larrest-start of the inverse cascade, respectively. Generally, Lbci agrees well with Linj in the midlatitude and high-latitude oceans, especially in the Northern Hemisphere. Leddy falls within the arrest ranges of the inverse cascade and is quite close to Larrest-start. Finally, the depth dependence and the anisotropy of the inverse kinetic energy cascade are also diagnosed in the global ocean. We have found that the strength of the inverse cascades decreases with increasing depth, but the global pattern of the strength is nearly invariable. Meanwhile, the variations in depth hardly affect the Linj and Larrest-start. After considering the anisotropy in the spectral flux calculation, a possible inertial range for the zonal spectral kinetic energy flux is expected, where the cascade magnitude will keep a nearly constant negative value associated with the oceanic zonal jets.