The Enhancement of Submesoscale Ageostrophic Motion on the Mesoscale Eddies in the South China Sea

Ageostrophic motion regulates the transformation of energy between large-scale geostrophic motion and dissipate scale motion. By combining surface drifters and satellite altimeter data, we present the characteristics of the submesoscale ageostrophic motion (SMAM) with a temporal scale of 2-7 day in the South China Sea (SCS). The SMAM enhances the strength of the mesoscale eddies, inducing negative vorticity for anticyclonic eddies and positive vorticity for cyclonic eddies. Spatially, SMAM is significant and explains more than 20% of the total kinetic energy in the Kuroshio branch zone. The geostrophic eddy kinetic energy is higher in western SCS than the Kuroshio zone, but the submesoscale EKE is lower, which is suggested to be influenced by the developing stage of mesoscale eddies. The dominant oscillation period of SMAM in the SCS and northwestern Pacific is 7-to 30 day intraseasonal variation. This spatiotemporal scale of SMAM is expected to be a good indicator for the simulation of oceanic circulation in submesoscale eddy-resolving models.

Automated summary

This study investigates the characteristics of submesoscale ageostrophic motion in the South China Sea using surface drifters and satellite altimeter data. The results show that this motion enhances the strength of mesoscale eddies and plays a significant role in their development.