Generation of second-mode internal solitary waves during winter in the northern South China Sea
Field measurements of second-mode internal solitary waves (mode 2 ISWs) during the winter on the upper continental slope of the northern South China Sea were reported in Yang et al. (J Geophys Res 114, 2009), but their generation mechanism remains elusive. We investigated this issue with a multi-modal evolution model and theoretical analysis, which suggest that the observed mode 2 ISWs were generated by a shoaling mode 2 semidiurnal internal tide (IT). The results show that two groups of mode 2 ISWs usually appear within one semidiurnal tidal period, successively riding on expanded and subsequently compressed pycnoclines. The number of wave groups largely depends on the amplitudes of the ITs, and a larger IT produces larger and more mode 2 ISWs. Furthermore, intermodal coupling dominates the evolution of a mode 1 IT, highlighting the importance of considering mode scattering in the propagation of low-mode ITs. Finally, the barotropic body force is calculated, and we deduce that the mode 2 semidiurnal IT originates from the Luzon Strait.
KeywordsSecond-mode internal solitary waves South China Sea
The WOA13 product, ETOPO1 global relief model, TEOS-10 software, and the OTIS regional tidal solutions for the China Seas were downloaded from the websites at https://www.nodc.noaa.gov/OC5/woa13/, https://www.ngdc.noaa.gov/mgg/global/global.html, http://www.teos-10.org, and http://volkov.oce.orst.edu/tides/region.html, respectively. The study was partially supported by grants from the Natural Science Foundation of Hainan Province Project (2016CXTD016), National Natural Science Foundation of China Project (41876201), and the Director Foundation of RADI. Finally, the authors wish to thank the two reviewers for their useful comments and suggestions.
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