Three-dimensional hindcast simulation of internal soliton propagationin the Asian Seas International Acoustics Experiment area

摘要

Internal solitary waves referred to as solitons are common occurrences in the SouthChina Sea. The Asian Seas International Acoustics Experiment (ASIAEX) experimentwas carried out in April-May 2001 to perform measurements on these solitons, which areoften highly energetic, having isopycnal displacements well over 100 m and phasespeeds greater than 2.5 m/s. Of particular interest is the interaction of a soliton with thesloping shelf bottom that occurs as the soliton shoals to water depths less than its waveheight. Observations during the experiment show that at such shallow depths, a solitonundergoes strong refraction and transformation. In this article, we present hindcastsimulation of a particular soliton observed during the experiment, using a fully nonlinear,nonhydrostatic, three-dimensional model and the actual bathymetry from the ASIAEXarea. The computation begins with the soliton at a distance about 100 km from the shelfand obtains the propagation and evolution of the soliton over the shelf-slope. Thethree-dimensional hindcast is able to reproduce the refraction of the soliton propagationobserved during the experiment as well as the propagation speed and direction in therange observed. The final nonlinear transformation of the soliton from symmetrical toskewed elongated waveform is also obtained in the model consistent with theobservations. The hindcast simulation reveals that the relative position of soliton'svorticity core to the local water depth is a crucial indicator of the onset of transformationand formation of elevation waves.