Experimental study of the vertical structure of internal solitary waves in the continuous pycnocline

Abstract

In order to reveal the complex structural characteristics of internal solitary waves (ISWs) in the actual ocean, an experimental study of the vertical structure of ISWs in the continuous pycnocline (a transition layer with sharp density changes) was conducted in a stratified fluid flume. The gravity collapse method was used to generate ISWs, and their wave-flow fields were measured using a coupled wave-flow measurement technique. The vertical structure of wave-flow fields was investigated as was the applicability of the Dubreil–Jacotin–Long (DJL) equation. The results show that the waveform of ISWs contains multiple isodensity lines that varied with fluid depth. The wave amplitude and wavelength of ISWs exhibited depth-dependent changes, which were negatively correlated. The vertical structure of the flow fields exhibited an approximate circular wave packet, with stronger horizontal flow than vertical flow. The larger the characteristic amplitude, the stronger the intensity of the flow field, and the faster the intensity of the vertical flow field increased. The applicability of the DJL equation was closely related to the stratified environment, with better agreement when the upper layer fluid constituted a larger ratio of the total fluid thickness.