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Journal of Oceanography

, Volume 75, Issue 6, pp 525–539 | Cite as

Upper ocean shear in the northern South China Sea

  • Anzhou Cao
  • Zheng Guo
  • Shuya Wang
  • Xu Chen
  • Xianqing Lv
  • Jinbao SongEmail author
Original Article

Abstract

The shear in the upper ocean of the northern South China Sea (SCS) is examined based on current observations from six moorings in 2010–2011. Spectral analysis results indicate that the sub-inertial currents, near-inertial waves (NIWs), diurnal and semidiurnal internal tides (ITs) dominate the current and shear in the northern SCS. Through comparing current variance and shear caused by these motions, this study shows the great contribution of NIWs to shear: Although NIWs only account for 2–7% of the total current variance, the shear caused by NIWs is approximate one fifth to one-quarter of the total shear. Moreover, the NIWs are dominated by the component with upgoing phase and downgoing energy, whereas the upgoing and downgoing components are comparable in both diurnal and semidiurnal ITs. Because the incoherent component has a larger contribution to shear than the coherent component, the shear of both diurnal and semidiurnal ITs exhibits significant signals with frequencies larger than the spring-neap cycles of approximate 14 days. The larger contribution to shear and smaller proportion in current variance suggest that the incoherent component of ITs has a larger vertical wavenumber than the coherent component. In addition, a case study shows that the mesoscale eddy pair occurring between 22 October and 2 December 2010 does not significantly enhance the ocean shear at two moorings especially below 150 m depth, although it contributes a lot to the current variance.

Keywords

Shear South China Sea Near-inertial wave Internal tide Incoherent component Mesoscale eddy 

Notes

Acknowledgements

This study is supported by the National Key Research and Development Program of China through Grants 2017YFA0604102, 2016YFC1401404 and 2016YFC1402304, and the National Natural Science Foundation of China through Grants 41806012 and 41876015. The authors deeply thank Physical Oceanography Laboratory as well as Professor Wei Zhao for providing the mooring observations. The authors also thank the Editor and two anonymous Reviewers for their insightful comments and valuable suggestions.

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Copyright information

© The Oceanographic Society of Japan and Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  1. 1.Ocean CollegeZhejiang UniversityZhoushanChina
  2. 2.Physical Oceanography Laboratory, Qingdao Collaborative Innovation Center of Marine Science and Technology (CIMST)Ocean University of China, Qingdao National Laboratory for Marine Science and TechnologyQingdaoChina

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