Abstract:
Wave breaking at the ocean--atmosphere interface injects air into the surface waters in the form of bubbles, altering the acoustical properties of the water. In situ sound-speed measurements at 3, 5, and 10 kHz were obtained in this dynamic near-surface layer using a moored sound-speed profiling buoy. The buoy was deployed in the North Atlantic during the winter of 1993-94 and obtained more than 40 days of data as part of the ASREX experiment. The record spans several storms, many with winds and significant wave heights in excess of 15 m/s and 7 m, respectively. Surface sound-speed measurements made in the first 7 m of the water column reveal large sound-speed reductions that are a result of air injection due to breaking waves. The data reveal the variable nature of the surface layer, both in short time scales O(seconds-minutes) that result from individual air-injection events, as well as longer time scales O(days) from one storm to another. Results of correlating the sound-speed field with environmental conditions will be discussed. The relationship between low-frequency, nondispersive sound speed and void fraction of air in water [A. B. Wood, A Textbook of Sound (1941)] make the resulting data useful for both oceanographers and acousticians. [Work supported by ONR.]