Direct observational evidence of an oceanic dual kinetic energy cascade and its seasonality

TL;DR

This study provides observational evidence of a dual kinetic energy cascade in the ocean, demonstrating energy transfer to both larger and smaller scales, with seasonal variations in transfer rates.

Contribution

First observational confirmation of a dual kinetic energy cascade in the ocean, revealing simultaneous inverse and forward cascades with seasonal modulation.

Findings

KE is injected at two dominant scales.

KE is transferred to both large and small scales.

Forward cascade dominates at scales smaller than 1-10 km.

Abstract

The Ocean's turbulent energy cycle has a paradox; large-scale eddies under the control of Earth's rotation primarily transfer kinetic energy (KE) to larger scales via an inverse cascade, while a transfer to smaller scales is needed to accomplish dissipation. It has been argued, using numerical simulations, that fronts, waves and other turbulent structures can produce a forward cascade of KE toward dissipation scales. However, this forward cascade and its coexistence with known inverse cascade were not confirmed in observations. Here we present the first evidence of a dual KE cascade in the Ocean by analyzing velocity measurements from surface drifters released in the Gulf of Mexico. Our results show that KE is injected at two dominant scales and transferred to both large and small scales, with the downscale flux dominating at scales smaller than ~1-10km. The cascade rates are modulated seasonally, with stronger KE injection and forward transfer during winter.