Internal solitary wave attenuation, spectral evolution, and induced flow fields beneath rigid ice covers

Abstract

The interaction between internal solitary waves (ISWs) and ice cover is an important process governing wave deformation, energy dissipation, and mixing in polar oceans. In this study, laboratory experiments were conducted in a strongly stratified silicone oil–water two-layer system using a rigid, nondeformable ice-cover model to examine the combined effects of ice-cover position and incident-wave amplitude on ISW evolution. Five dimensionless ice-cover positions and four incident-wave amplitudes were considered. Image-based interface extraction, particle image velocimetry, and wavelet analysis were used to quantify waveform evolution, spatial amplitude attenuation, spectral redistribution, and flow-field responses. The results show that the vertical position of the ice cover strongly regulates the transition of ISWs from stable propagation to instability-dominated evolution. Four representative regimes were identified: wave flattening, wave reflection, interfacial instability, and wave breaking. Under upper-layer ice-cover conditions (hi/h1 = 0.4, 0.6), wave-height attenuation was relatively limited, with the downstream normalized amplitude remaining at approximately 0.85–0.95. In contrast, when the ice cover was located near or below the density interface (hi/h1 = 0, −0.4, and −0.6), the normalized amplitude decreased sharply to approximately 0.50–0.65, indicating substantially enhanced wave deformation, reflection, and localized energy dissipation. Increasing the incident-wave amplitude further intensified nonlinear wave–ice interaction, producing stronger waveform distortion, broader wavelet spectra, and more fragmented vortical structures. These findings demonstrate that ice-cover position mainly controls the attenuation pathway and dissipation mode of ISWs, while incident-wave amplitude regulates the strength of nonlinear instability and spectral energy redistribution beneath ice-covered waters.