Region-dependent eddy kinetic energy budget in the northeastern South China Sea revealed by submesoscale-permitting simulations

Mesoscale eddies are active in the northeastern South China Sea (NESCS) and play an important role in the oceanic energy balance therein. In this study, the budgets of mesoscale eddy kinetic energy (EKE) in the NESCS were explored by simultaneously considering the interactions with both large-scale and submesoscale processes based on high-resolution simulations. We found that the regions southwest of Taiwan (SWT) and Luzon Strait (LS) are two energy-cascading hotspots, but they present quite different EKE budgets. Specifically, in the SWT, which has strong EKE, the baroclinic conversion associated with the release of available potential energy is the dominant EKE source, while the barotropic conversion between large-scale and mesoscale processes (BTLM) and the wind stress work are the main EKE sinks. In addition, submesoscale processes are found to transfer energy reversely to mesoscale eddies, but at lower magnitudes. For the LS, which shows complicated island topography and energetic large-scale and submesoscale activities, the BTLM is the dominant EKE source, while the transfer of energy to submesoscale processes is an important EKE sink. This means that the kinetic energies in these two regions display opposing cascading directions. The cascade direction is inverse, from submesoscale to large-scale, in the SWT and forward, from large-scale to submesoscale, in the LS. These results expand our understanding of the EKE balance and energy cascade in the NESCS among multiscale dynamic processes and offer beneficial implications for improving parameterizations in ocean circulation models.

Automated summary

This study explores the budgets of mesoscale eddy kinetic energy in the northeastern South China Sea and reveals two energy-cascading hotspots, Taiwan southwest and Luzon Strait. The study finds that the dominant source of kinetic energy differs between the two hotspots, with baroclinic conversion being dominant in Taiwan southwest and barotropic conversion and wind stress work being dominant in Luzon Strait. Additionally, submesoscale processes transfer energy reversely to mesoscale eddies, but at lower magnitudes.