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.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Alford, M. H., 2001. Internal swell generation: The spatial distribution of energy flux from the wind to mixed layer nearinertial motions. Journal of Physical Oceanography, 31 (8): 2359–2368.
Alford, M. H., and Gregg, M. C., 2001. Near-inertial mixing: Modulation of shear, strain and microstructure at low latitude. Journal of Geophysical Research, 106 (C8): 16947–16968.
Chen, G., Xue, H., Wang, D., and Xie, Q., 2013. Observed near-inertial kinetic energy in the northwestern South China Sea. Journal of Geophysical Research: Oceans, 118 (10): 4965–4977.
D’Asaro, E. A., 1985. The energy flux from the wind to nearinertial motions in the surface mixed layer. Journal of Physical Oceanography, 15 (8): 1043–1059.
Flierl, G. R., 1978. Models of vertical structure and the calibration of two-layer models. Dynamics of Atmospheres and Oceans, 2 (4): 341–381.
Gill, A. E., 1984. On the behavior of internal waves in the wakes of storms. Journal of Physical Oceanography, 14 (7): 1129–1151.
Gonella, J., 1972. A rotary-component method for analysing meteorological and oceanographic vector time series. Deep Sea Research and Oceanographic Abstracts, 19 (12): 833–846.
Guan, S., Zhao, W., Huthnance, J., Tian, J., and Wang, J., 2014. Observed upper ocean response to typhoon Megi (2010) in the Northern South China Sea. Journal of Geophysical Research: Oceans, 119 (5): 3134–3157.
Large, W. G., and Pond, S., 1981. Open ocean momentum flux measurements in moderate to strong winds. Journal of Physical Oceanography, 11 (3): 324–336.
Leaman, K. D., and Sanford, T. B., 1975. Vertical energy propagation of inertial waves: A vector spectral analysis of velocity profiles. Journal of Geophysical Research, 80 (15): 1975–1978.
Oey, L. Y., Ezer, T., Wang, D. P., Fan, S. J., and Yin, X. Q., 2006. Loop current warming by Hurricane Wilma. Geophysical Research Letters, 33 (8): 153–172.
Pollard, R. T., 1980. Properties of near-surface inertial oscillations. Journal of Physical Oceanography, 10 (3): 385–398.
Pollard, R. T., and Millard, R. C., 1970. Comparison between observed and simulated wind-generated inertial oscillations. Deep Sea Research and Oceanographic Abstracts, 17 (4): 813–821.
Powell, M. D., Vickery, P. J., and Reinhold, T. A., 2003. Reduced drag coefficient for high wind speeds in tropical cyclones. Nature, 422 (6929): 279–283.
Sanford, T. B., Price, J. F., and Girton, J. B., 2011. Upper-ocean response to Hurricane Frances (2004) observed by profiling EM-APEX floats. Journal of Physical Oceanography, 41 (6): 1041–1056.
Shay, L. K., Mariano, A. J., Jacob, S. D., and Ryan, E. H., 1998. Mean and near-inertial ocean current response to Hurricane Gilbert. Journal of Physical Oceanography, 28 (5): 858–889.
Su, J., 2004. Overview of the South China Sea circulation and its influence on the coastal physical oceanography outside the Pearl River Estuary. Continental Shelf Research, 24 (16): 1745–1760.
Sun, Z., Hu, J., Zheng, Q., and Li, C., 2011. Strong near-inertial oscillations in geostrophic shear in the northern South China Sea. Journal of Oceanography, 67 (4): 377–384.
Teague, W. J., Jarosz, E., Wang, D. W., and Mitchell, D. A., 2007. Observed oceanic response over the upper continental slope and outer shelf during Hurricane Ivan. Journal of Physical Oceanography, 37 (9): 2181–2206.
Torrence, C., and Compo, G. P., 1998. A practical guide to wavelet analysis. Bulletin of the American Meteorological Society, 79 (1): 61–78.
Xie, X. H., Shang, X. D., Haren, H. V., Chen, G. Y., and Zhang, Y. Z., 2011. Observations of parametric subharmonic instability-induced near-inertial waves equatorward of the critical diurnal latitude. Geophysical Research Letters, 38 (5): 132–140.
Xu, Z., Yin, B., Hou, Y., and Xu, Y., 2013. Variability of internal tides and near-inertial waves on the continental slope of the northwestern South China Sea. Journal of Geophysical Research: Oceans, 118 (1): 197–211.
Zhang, Z., Zhao, W., Tian, J., and Liang, X., 2013. A mesoscale eddy pair southwest of Taiwan and its influence on deep circulation. Journal of Geophysical Research: Oceans, 118 (12): 6479–6494.
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.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
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
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11802-017-3153-7