Experimental study for the breaking properties of internal solitary waves flowing over a bottom step

Abstract

The breaking properties of internal solitary waves (ISWs) flowing over a bottom step were investigated experimentally. The experiments were performed in a two-layer immiscible system to avoid the influence of diffusion and mixing. The flat bottom condition and the bottom step condition had been conducted respectively. The characteristics of incident ISWs, the process of breaking and the subsequent developments were taken into discussion. A modified internal Iribarren number was introduced, and the critical condition of breaking was considered to be related to its trend change point. The initial stage of the breaking process was found can be divided into spatially discrete characteristic structures other than messy flowing of the full interface. And the characteristic structures have close horizontal lengths for different amplitudes. The horizontal velocity gradient was identified as the key parameter of shear instability. By analyzing the subsequent developments, the completely broken ISWs were found can reform a quasi ISWs propagating upon the bottom step which has a smooth front-face and an ever-breaking back-face. Due to the breaking of the back-face, the amplitude of reformed ISWs continues to decrease. Meanwhile, the attenuation rate was noticed to be related to the incident amplitude, but not be related to whether it is broken or the degree of breaking.