Influence of internal solitons on sound propagation in shallow water with a summer strong thermocline

Abstract

Analysis of extensive data has shown that the internal waves in the coastal zone exhibit the properties of solitons. Using experimental data and numerical simulation results, this paper shows what happens to sound propagation if internal solitons are present in shallow water with a strong summer thermocline. The experiments were conducted in the Yellow Sea off the China coast during the summer, where strong thermoclines with more than 10 °C temperature difference are often present. In order to provide a clear physical picture on the true problem, a carefully chosen simple ocean model is used to show the resonant interaction of sound waves with internal solitons, including signal frequency, soliton wavelength, and packet length resonances. Then, the numerical model is extended to include the classic characteristic properties of more realistic ocean soliton packets. Under the resonance condition acoustic mode coupling transfers a significant amount of energy from lower modes into higher-order modes that have much larger attenuation rates. This becomes a new attenuation mechanism for shallow water with a strong thermocline. The ‘‘resonancelike’’ behavior predicted by the PE analysis is consistent with mode coupling theory. [Work supported by ONR and IAAS.]