The Enhancement of Submesoscale Ageostrophic Motion on the Mesoscale Eddies in the South China Sea. Issue 9 (13th September 2022)

• Record Type: Journal Article
• Authors: Qiu, Chunhua; Yang, Zihao; Wang, Dongxiao; Feng, Ming; Su, Jingzhi
• Is Part Of: Journal of geophysical research. Volume 127:Issue 9(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-13
• Subjects: South China Sea -- submesoscale ageostrophic motion -- intraseasonal variability -- mesoscale eddy; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2022JC018736
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: 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. Plain Language Summary: Mesoscale eddies with horizontal scale of 50–300 km and temporal scale >1 month, could transport oceanic energy, heat and salt. As the development of observations and numerical models, fine structures in terms of submesoscale structures become hot issue due to its strong vertical velocity. We aim to understand the contribution of submesoscale ageotrophic motion (SMAM) to mesoscale eddies in the South China Sea in this study. The SMAM appears more often at the position of 0.8 times radius of mesoscale eddies, and it enhances the strength of the mesoscale eddies via regulating the relative vorticity. Spatially, the kinetic energy induced by SMAM has the largest value in the Kuroshio branch zone, where easily produces young mesoscale eddies. The SMAM has a 7‐to 30 day intraseasonal variation. This spatiotemporal scale of SMAM is expected to be a good indicator in submesoscale eddy‐resolving models. Key Points: Most submesoscale ageostrophic motion (SMAM) appears within 0.5–1 times the radius of mesoscale eddies SMAM enhances the strength of anticyclonic and cyclonic eddies The SMAM presents significant 7‐to 30 days intraseasonal variability