Global Cascade of Kinetic Energy in the Ocean and the Atmospheric Imprint

TL;DR

This study estimates the ocean's kinetic energy transfer across scales from 10 km to 40,000 km, revealing a significant energy cascade influenced by atmospheric cells and seasonal cycles, with implications for understanding oceanic energy dynamics.

Contribution

First comprehensive estimate of oceanic kinetic energy transfer across a wide range of scales, highlighting the role of atmospheric forcing and seasonal variability in energy cascades.

Findings

Peak upscale transfer of 300 GW at 120 km scale.

Energy transfer exhibits a self-similar seasonal cycle.

Most cascade activity occurs south of 15°S.

Abstract

We present the first estimate for the ocean's global scale-transfer of kinetic energy (KE), across scales from 10~km to 40000~km. We show the existence of oceanic KE transfer between gyre-scales and mesoscales induced by the atmosphere's Hadley, Ferrel, and polar cells, and intense downscale KE transfer associated with the Inter-Tropical Convergence Zone. We report peak upscale transfer of 300 GigaWatts across mesoscales of 120~km in size, roughly 1/3rd the energy input by winds into the oceanic general circulation. This "cascade" penetrates almost the entire water column, with nearly three quarters of it occurring south of 15$^\circ$S. The mesoscale cascade has a self-similar seasonal cycle with characteristic lag-time of $\mathbf{\approx27~}$days per octave of length-scales such that transfer across 50~km peaks in spring while transfer across 500~km peaks in summer. KE content of those mesoscales follows the same self-similar cycle but peaks $\mathbf{\approx40~}$days after the peak cascade, suggesting that energy transferred across a scale is primarily deposited at a scale 4$\times$ larger.