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Observation of near-inertial internal waves on the continental slope in the northwestern South China Sea

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Abstract

Based on nearly 3 months of moored acoustic Doppler current profiler records on the continental slope in the northwestern South China Sea (SCS) in 2006, this study examines temporal and vertical characteristics of near-inertial internal waves (NIW). Rotary frequency spectrum indicates that motions in the near-inertial frequency are strongly polarized, with clockwise (CW) energy exceeding counterclockwise (CCW) by about a factor of 10. Wavelet analysis exhibits an energy peak exceeding the 95% confidence level at the frequency of local inertial during the passage of typhoon Xangsane (24 September to 4 October). This elevated near-inertial kinetic energy (NIKE) event possesses about a 4 days delay correlation with the time integral of energy flux induced by typhoon, indicating an energy source of wind. Further analysis shows that the upward phase velocity of this event is 3.8 m h−1 approximately, corresponding to a vertical wavelength of about 125 m if not taking the redshift of local inertial frequency into account. Rotary vertical wavenumber spectrum exhibits the dominance of clockwise-with-depth energy, indicating downward energy propagation and implying a surface energy source. Dynamical modes suggest that mode 1 plays a dominant role at the growth stage of NIW, whereas major contribution is from higher modes during the penetration of NIKE into the ocean interior.

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Acknowledgements

This work is supported by the National Key Basic Research Program of China (Program 973) (Grant No. 2014 CB745003), the National Key Scientific Instrument and Equipment Development Project (Grant No. 2012YQ120 03909), the National High Technology Research and Development (863) Program of China (Grant Nos. 2013AA 09A502, 2013AA09A501), and the Global Change and Air-Sea Interaction Project (Grant No. GASI-03-01-01-03). Insightful comments from anonymous reviewers are very helpful in improving the work.

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  1. Physical Oceanography Laboratory, Ocean University of China, Qingdao, 266100, P. R. China

    Jie Zheng, Jiwei Tian & Hui Liang

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  1. Jie Zheng
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  2. Jiwei Tian
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  3. Hui Liang
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Correspondence to Hui Liang.

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Zheng, J., Tian, J. & Liang, H. Observation of near-inertial internal waves on the continental slope in the northwestern South China Sea. J. Ocean Univ. China 16, 184–190 (2017). https://doi.org/10.1007/s11802-017-3153-7

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  • DOI: https://doi.org/10.1007/s11802-017-3153-7

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