Periodic Mesoscale Eddies in the South China Sea

• Published in: Journal of geophysical research. Oceans 2020-01, Vol.125 (1), p.n/a
• Main Authors: Chu, Xiaoqing, Chen, Gengxin, Qi, Yiquan
• Format: Article
• Language: English
• Subjects: Aerodynamics; Annual variations; Asian monsoons; Biology; Climate variations; Eddies; Fisheries; Geophysics; interannual variability; Interannual variations; Mesoscale eddies; mesoscale eddy; Mesoscale phenomena; Monsoon circulation; Monsoons; Ocean circulation; periodic eddy; Physics; Satellite observation; Satellites; South China Sea; Variation; vertical structure; Vortices; Wind; Winter; Winter monsoon
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2019JC015139

Although numerous mesoscale eddies are observed in the South China Sea (SCS), a comprehensive study that focuses on periodic eddies has not yet been reported. Periodic eddies are a type of eddies that occur nearly annually in fixed time frames with similar patterns and trajectories. On the basis of in situ and satellite observations, this paper reports a periodic anticyclonic eddy in the western SCS (the Western SCS Anticyclonic Eddy, WAE) and elucidates the underlying processes responsible for its generation and evolution. The WAE is a seasonal phenomenon modulated by the Asian monsoon and basin‐scale circulation. Usually, the WAE generates around 112°E, 14°N in February–March, induced by the cyclonic gyre in the northern SCS associated with the winter monsoon. The WAE occupies the western SCS for 5 months and finally dissipates in July due to the reversal of the monsoon and thus the circulation transition. The WAE shows important interannual variations associated with large‐scale climate variation, and the Niño‐3.4 index could be a potential predictor for its interannual variation. Finally, we summarize 13 periodic eddies in the SCS, including those unreported by previous studies. The period eddies in the SCS exhibit an inverse “L” shape vortex train structure along the western boundary and around the 17°N section, with an anticyclonic “phase” in summer and a cyclonic “phase” in winter. This study provides new knowledge for periodic eddies in the SCS and will benefit targeted observations of periodic eddies. Plain Language Summary Some mesoscale eddies in the ocean are observed to occur nearly annually, we here call them periodic eddies. Due to high occurrence rates, those periodic eddies have profound impacts on local physics, fishery, biology, and air‐sea interaction. This study first reports a periodic anticyclonic eddy in the western South China Sea from in situ and satellite observations. By eddy reoccurrence rate, we then summarized all periodic eddies in the SCS. These eddies form the mean state of the mesoscale eddy field in the SCS. This study provides new knowledge for periodic eddies in the SCS and it also carries implications for future studies of periodic eddies in other regions. Key Points A periodic anticyclonic eddy in the western South China Sea was documented by in situ measurements There are 13 periodic mesoscale eddies and they form the mean state of the eddy field in the South China Sea The period eddies in the SCS exhibit an inverse