Interannual variation of the South China Sea circulation during winter: intensified in the southern basin
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Surface geostrophic current derived from altimetry remote sensing data, and current profiles observed from in-situ Acoustic Doppler Current Profilers (ADCP) mooring in the northern South China Sea (NSCS) and southern South China Sea (SSCS) are utilized to study the kinetic and energetic interannual variability of the circulation in the South China Sea (SCS) during winter. Results reveal a more significant interannual variation of the circulation and water mass properties in the SSCS than that in the NSCS. Composite ananlysis shows a significantly reduced western boundary current (WBC) and a closed cyclonic eddy in the SSCS at the mature phase of El Niño event, but a strong WBC and an unclosed cyclonic circulation in winter at normal or La Niña years. The SST is warmer while the subsurface water is colder and fresher in the mature phase of El Niño event than that in the normal or La Niña years in the SSCS. Numerical experiments and energy analysis suggest that both local and remote wind stress change are important for the interannual variation in the SSCS, remote wind forcing and Kuroshio intrusion affect the circulation and water mass properties in the SSCS through WBC advection.
KeywordsInterannual variability South China Sea Winter monsoon Western boundary current ENSO
We are grateful to the editor and anonymous reviewers for their valuable suggestions and comments which greatly help to improve the manuscript. We also thank Xiaopei Lin for his helpful discussion. We benefited from numerous data sets made freely available, including AVISO (http://www.aviso.altimetry.fr/en/data/data-access.html), TMISST (http://apdrc.soest.hawaii.edu/datadoc/trmm_tmi_mon.php), CCMP (http://www.remss.com/measurements/ccmp/), OAFlux (http://oaflux.whoi.edu/heatflux.html). The numerical simulation is supported by the high-performance computing division and Ms. Dandan Sui of the South China Sea Institute of Oceanology. This study is jointly supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA11010302, XDA11010304), the National Natural Science Foundation of China (41521005, 41476013, 41576002, 41576012, 41628601, 41776025). The Guangdong Natural Science Funds for Distinguished Yong Scholar (2014A030306049).
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