High-frequency Internal Waves, High-mode Nonlinear Waves and K-H Billows on the South China Sea's Shelf Revealed by Marine Seismic Observation

Abstract

Abstract. From July to September 2009, a set of multi-channel seismic data was collected in the northern shelf area of the South China Sea. After the data was processed, we observed a series of shoaling events on one of the survey lines, including high-frequency internal waves, high-mode nonlinear internal waves, and shear instability. Using theoretical results from previous numerical simulations and field observations, coupled with local temperature and salinity data, we analyzed their depth distribution, waveform characteristics, and formation mechanisms, and discussed the influence of seafloor topography and stratification on the shoaling of solitary internal waves. We estimated the mixing parameters of seawater using a parameterization scheme based on hydrographic data and seismic data, respectively. And we found that the diapycnal mixing caused by these shoaling events in the shelf area were about 3.5 times greater than those on the slope. Consequently, the fission of internal solitary waves and the induced shear instability serve as significant mechanisms for the energy dissipation of internal solitary waves at the slope and shelf of the South China Sea. Additionally, the high-frequency internal waves generated during shoaling might also have a crucial role in this process.