512 / 2024-09-18 09:42:30

Interaction between balanced and unbalanced motions and its associated cross-scale kinetic energy transfer

cross-scale; kinetic energy fluxes; multiscale interactions; Kuroshion Extension; Southern China Sea.

 

Between the Kuroshio Extension and its recirculation gyres, balanced motions (BMs) interactions, as typified by eddy-eddy and eddy-mean flow interactions, have been well-observed and well-modeled, with their prominence clearly evidenced. By contrast, The Luzon Strait in the South China Sea (SCS) is well-known as one of the regions with the most energetic internal tides in the global ocean, resulting in strong unbalanced motions (UBMs). Using a newly-developed dynamical decomposition, we disentangle vortical and wavy motions in oceanic flows and quantify the cross-scale kinetic energy (KE) fluxes induced by multiscale nonlinear interactions under the coarse-graining framework based on a submesoscale-permitting numerical simulation (MITgcm llc4320).  In this study, we assess the contributions of vortical motion, wavy motion, and their interactions to cross-scale KE fluxes, as vortical and wavy motions largely represent BMs and UBMs , respectively. We find that KE undergoes an inverse energy cascade that are dominated by vortical motions, as described by quasi-geostrophic theory. Additionally, BMs-UBMs interactions can generate significant forward energy cascades which serve as an effective mechanism for energy dissipation occurring within the ocean interior.