On the stability of long-range sound propagation through a structured ocean

Several acoustic experiments show a surprising degree of stability in wave fronts propagating over multi-megameter ranges through the ocean's sound ch annel despite the presence of random-like, sound-speed fluctuations. Previo us works have pointed out the existence of chaos in simplified ray models i ncorporating structure inspired by the true ocean environment. A ''predicta bility horizon'' has been introduced beyond which stable wavefronts cease t o exist and point-wise, detailed comparisons between even the most sophisti cated models and experiment may be limited for fundamental reasons. By appl ying one of the simplified models it is found that, for finite ranges, the fluctuations of the ray stabilities are very broad and consistent with log- normal densities. A fraction of the ray density retains a much more stable character than the typical ray. This may be one of several possible mechani sms leading to greater than anticipated sound-field stability. The log-norm al ray stability density may underlie the recent, experimentally determined , log-normal density of wave-field intensities [Colosi et al., J. Acoust. S ec. Am. 105, 3202-3218 (1999)]. (C) 2001 Acoustical Society of America.