Analyzing amplitudes of internal solitary waves in the northern South China Sea by use of seismic oceanography data

In the northern South China Sea, numerous multichannel seismic reflection sections are used to identify internal solitary wave (ISW) packets and extract wave amplitudes and corresponding water depths. The analyzed data show that these depression ISWs occur on the upper continental slope at water depths between 263 m and 740 m, with maximum amplitudes ranging from 35 m to 128 m. Our results, in conjunction with previous studies, suggest that the maximum amplitudes of the ISWs on the northern South China Sea continental slope are highly correlated with seafloor depths and that they have a logarithmic function relationship. The maximum amplitudes decrease with decreasing water depths. Interactions between the ISWs and the seafloor play a crucial role in decreasing ISW maximum amplitudes, especially in shallow areas. In addition, we compare the observed vertical amplitude distribution with theoretical results and find that they are concordant. The "bottom depth" (H) in the boundary conditions of eigenfunctions represents the extension depth of the ISW rather than the actual seafloor depth. Here, the ISW extension depth is where the ISW amplitude becomes zero and the seafloor depth is just under the ISW. If the ISW interacts intensely with the seafloor, its observed vertical amplitude distribution may exhibit prominent differences from the theoretical result.