Bidirectional Kinetic Energy Cascade in Ocean Surface Circulation Revealed by Surface Drifters

Wei Wu1,2, Alberto Naveira Garabato2
1South China Sea Institute of Oceanography, Chinese Academy of Sciences
2University of Southampton

Oceanic kinetic energy (KE) cascades play a crucial role in the transfer of energy across various spatial scales in the upper ocean. At the mesoscale (approximately 50-300 km), KE is predominantly transferred to larger-scale ocean currents (inverse cascades). In contrast, at the submesoscale (approximately 1-10 km), both forward (downscale) and inverse (upscale) KE cascades can occur, facilitating energy transfer to both smaller and larger scales. Understanding these KE cascades is essential for comprehending the formation and evolution of ocean currents, and the overall dynamics of ocean circulation. Previous studies have primarily investigated ocean surface KE cascades using numerical simulations or regional observations, resulting in a lack of comprehensive global assessments. In this study, we analyze in situ velocity measurements from surface drifters to characterize the global distribution of dual KE cascades. This study reveals that western boundary currents regions exhibit pronounced inverse and forward KE cascade magnitudes. It indicates that eddy generated from eastern boundary moved westward. In submesoscale, eddy will interact with topography then dissipation, which caused KE transferring to smaller scale. Meanwhile, eddy can transport KE to larger scale via eddy-eddy triad interaction. Additionally, we observe that KE cascade rates undergo seasonal modulation, with enhanced KE injection and downscale energy transfer during winter months. These insights contribute to a more comprehensive understanding of global ocean surface dynamics and energy transfer processes.