A numerical study of the South China Sea Warm Current during winter monsoon relaxation
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Using a Finite-Volume Community Ocean Model, we investigated the dynamic mechanism of the South China Sea Warm Current (SCSWC) in the northern South China Sea (NSCS) during winter monsoon relaxation. The model reproduces the mean surface circulation of the NSCS during winter, while model-simulated subtidal currents generally capture its current pattern. The model shows that the current over the continental shelf is generally southwestward, under a strong winter monsoon condition, but a northeastward counter-wind current usually develops between 50-and 100-m isobaths, when the monsoon relaxes. Model experiments, focusing on the wind relaxation process, show that sea level is elevated in the northwestern South China Sea (SCS), related to the persistent northeasterly monsoon. Following wind relaxation, a high sea level band builds up along the mid-shelf, and a northeastward current develops, having an obvious vertical barotropic structure. Momentum balance analysis indicates that an along-shelf pressure gradient provides the initial driving force for the SCSWC during the first few days following wind relaxation. The SCSWC subsequently reaches a steady quasi-geostrophic balance in the cross-shelf direction, mainly linked to sea level adjustment over the shelf. Lagrangian particle tracking experiments show that both the southwestward coastal current and slope current contribute to the northeastward movement of the SCSWC during winter monsoon relaxation.
Keywordnorthern South China Sea South China Sea Warm Current monsoon relaxation numerical model pressure gradient barotropic structure
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We thank the Ocean University of China’s Physical Oceanography Laboratory Ocean Data and Simulation Center for providing the hardware support. We also thank Asia-Pacific Data-Research Center (APDRC) of the International Pacific research Center, Center for Earth Information Science and Technology (CEIST), Geophysical Fluid Simulation Research Group (GFSG), NASA’s Making Earth Science data records for Use in Research Environments (MEaSUREs) Program, NOAA’s National Center for Environmental Information (NCEI), and the China Argo Real-time Data Center for providing valuable data for this study.
- Guan B X, Chen S J. 1964. The Current Systems in the Nearsea Area of China Seas. Initial Report 5. Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China. p.1–85. (in Chinese)Google Scholar
- Guan B X. 1978. The warm current in the South China Sea-a current flowing against the wind in winter in the open sea offGuangdong Province. Oceanol. Limnol. Sin., 9 (2): 117–127. (in Chinese with English abstract)Google Scholar
- Guan B X. 1985. Some features of the temporal and spatial distributions of the “counter-wind” current in northern South China Sea in winter. Oceanol. Limnol. Sin., 16 (6): 429–438. (in Chinese with English abstract)Google Scholar
- Guan B X. 2002. Winter Counter-Wind Current offthe Southeastern China Coast. China Ocean University Press, Qingdao, China. 267p. (in Chinese)Google Scholar
- Guo Z X, Yang T H, Qiu D Z. 1985. The South China Sea warm current and the SW-ward current on its right side in winter. Tropical Oceanology, 4 (1): 1–9. (in Chinese with English abstract)Google Scholar
- He Q, Wei Z X, Wang Y G. 2012. Study on the sea currents in the northern shelf and slope of the South China Sea based on the observation. Acta. Oceanol. Sin., 34 (1): 17–28. (in Chinese with English abstract)Google Scholar
- Li R X, Chen C S, Xia H Y, Beardsley R C, Shi M C, Lai Z G, Lin H C, Feng Y Q, Liu C J, Xu Q C, Ding Y, Zhang Y. 2014. Observed wintertime tidal and subtidal currents over the continental shelf in the northern South China Sea. J. Geophys. Res., 119 (8): 5289–5310, https://doi.org/10.1002/2014JC009931. CrossRefGoogle Scholar
- Su J L, Liu X B. 1992. Numerical simulation of circulation in the South China Sea. In: Zeng Q C ed. Proceedings of Symposium on Ocean Circulation. China Ocean Press, Beijing, China. p.206–215. (in Chinese)Google Scholar
- Su J Z, Lu J, Hou Y J, fang G H, Wei Z X, Yin B S. 2002. Analysis of satellite-tracked drifting buoys in the South China Sea. Oceanol. Limnol. Sin., 33 (2): 121–127. (in Chinese with English abstract)Google Scholar
- U.S. Naval Oceanographic Office and the U.S. 1983. Naval Ocean Research and Development Activity. DBDB5 (Digital Bathymetric Data Base-5 Minute Grid). U. S. Naval Oceanographic Office, Bay St. Louis. 329p.Google Scholar
- Wyrtki K. 1961. Physical oceanography of the Southeast Asian water. In: Wyrtki K ed. NAGA Report: Scientific Result of Marine Investigation of the South China Sea and Gulf of Thailand 1959-1961. Scripps Institution of Oceanography, California, United States. p.155–160.Google Scholar
- Xiong X J. 2013. The circulation structure and mechanism studies on the China Seas. Ocean University of China, Qingdao, China. 208p. (in Chinese)Google Scholar
- Yang K C. 2006. The non-persistent South China Sea warm current. National Taiwan University, Taipei, China. 49p.Google Scholar
- Zhong H L. 1990. Structures of the density circulation. In: Ma Y L ed. Report of Decadal Hydrographic Series Survey of the Shelf and Adjacent Waters of the Northern South China Sea. China Ocean Press, Beijing, China. p.215–241. (in Chinese)Google Scholar