Stagnation of Eddy Kinetic Energy After Summer Monsoon Onset in the South China Sea

The monsoon is the primary force behind the upper-layer circulation system and regulates eddy activity in the South China Sea (SCS). Using satellite observations and a state-of-the-art oceanic reanalysis, this study examines transferring processes of eddy kinetic energy (EKE) during the SCS Summer Monsoon (SCSSM) onset (20th May on average). The SCSSM onset transforms surface winds from easterly to southwesterly, increasing EKE in the southwestern SCS by surface wind work. Despite the persistent energy input from wind work, EKE growth ceases during the first 20 days after SCSSM onset. An EKE budget analysis suggests that most energy input dissipates in the mixed layer due to the high wind speed, which explains the EKE stagnation. Additionally, eddy-mean flow interactions transfer kinetic energy from eddies to mean flows during the SCSSM onset. The Vietnam coastal upwelling system provides available potential energy to EKE on the offshore side through buoyancy work. Our study reveals energy-transferring processes from the summer monsoon to eddy activity and dissipation in the SCS, with implications for understanding multiscale dynamic evolutions during the monsoon transition. The South China Sea (SCS) has received much attention for its unique ocean dynamics impacted by monsoons. While the SCS monsoon is known to modulate the seasonal variation in SCS circulation, the effects of the intraseasonal monsoon oscillations on the oceanic eddy activity remain unclear. Generally, ocean circulation and eddy activity get stronger when surface winds strengthen. However, this study reports a stagnation of eddy kinetic energy (EKE) after the SCS summer monsoon onset in the southern SCS despite the persistent energy input from the surface winds. EKE budget results show that high-speed wind changes the current structure and greatly intensifies ocean dissipation. This study provides a new perspective on ocean energy-transferring processes under the SCS monsoon transition and will benefit ocean circulation modeling and prediction in the future. Eddy kinetic energy (EKE) growth stagnates for 20 days in eastern Vietnam after the South China Sea Summer Monsoon onset Dissipation due to the high wind speed explains the EKE stagnation as a dominant energy sink The formation of the upwelling system changes the energy transfer process and modulates the eddy-mean flow interaction