Numerical study on the surface signature of internal solitary waves

Abstract

The propagation of internal solitary waves (ISWs) underwater and their interactions with surface waves can affect the sea surface state and generate distinct surface signatures of bright–dark striped patterns in remote sensing imagery. These patterns have been one of the most important methods for wide coverage detection and observation of ISWs. This study establishes a fully nonlinear numerical model for ISW–surface wave interaction simulation based on the multi-domain boundary element method. By numerical simulation, the formation mechanism, characteristics, and influencing factors of ISW surface signatures are revealed. The physical essence of the ISW surface signature is the spatially inhomogeneous wavelength and roughness changes in the surface waves due to the convergence and divergence effects of the ISW. Based on the surface wave wavelength changes, the surface area affected by an ISW is divided into three regions from front to back—the converging, diverging, and restoring regions—corresponding to the regions where the surface waves are compressed, stretched, and recover, respectively. By comparing different cases, it is found that the ISW amplitude, surface wave amplitude, and surface wave wavelength are the main factors influencing the ISW surface signature. ISWs with larger amplitudes have stronger convergence and divergence effects on surface waves, making the overall scale of the ISW surface signature larger. Larger surface wave amplitudes provide stronger resistance to the ISW divergence effect and lead to smaller diverging regions, and larger surface wave wavelengths make the converging region larger and the diverging and restoring regions smaller.