Nonlinear internal solitary waves in the northeast South China Sea near Dongsha Atoll using seismic oceanography

Abstract

We studied nonlinear internal solitary waves in the northeast South China Sea near Dongsha Atoll, mainly using seismic oceanography. The type of internal solitary wave examined was the first mode depression wave, with maximum amplitude 85.5 m. From the depth of this amplitude and below, the amplitude of solitary waves generally decreased linearly, and the rate of decrease with depth was about 0.2. The seafloor can influence the waveforms of these waves. Specifically, the seafloor can cut the bottom of solitary waves, making them discontinuous, and the seafloor friction can induce many short waves near it. The apparent width of solitary waves directly from seismic sections should be corrected to obtain true width. Apparent widths of two solitary waves studied were 4.52 and 3.36 km; these were about 0.5-3 km after correction. There was vertical noise at solitary wave locations, reflecting strong vertical shear forces there. The contrast between horizontal wavenumber spectra of the solitary waves and GM (Garrett Munk) model spectra indicate that their wave energy was about two orders of magnitude larger than the GM spectra at low wave numbers.