The effect of internal wave time dependence on ray chaos

Abstract

A range-dependent field of sound speed in the ocean can give rise to chaotic instabilities in acoustic ray paths. A model of internal waves is used as a range-dependent effect on the speed of sound in numerical simulations. These simulations, performed over a 1000-km range, demonstrate the sensitivity of ray paths to slight changes in the sound-speed field or the initial conditions of their launch. Previous work [Simmen et al. (1999)] has shown the effect on arrival depth of slightly shifting the launch angle of each ray. The focus of this work is the effect of internal wave time dependence. Comparisons are made between simulations using a time-dependent medium and those using a time-independent (‘‘frozen’’) medium, and between simulations with different geophysical starting times. The resulting arrival depth differences are compared to those induced by launch angle shifts. The structure and magnitude of these differences are considered in the case of two different sound-speed profiles: a Munk canonical profile and a profile from the Slice89 experiment.