ASA 124th Meeting New Orleans 1992 October

3aAO18. Arctic ring eddies and acoustic ambient noise.

Richard D. Doolittle

6691 Mac Arthur Blvd., Bethesda, MD 20816

Morris Schulkin

Ocean Acoust., Inc., 9325 Orchard Brook Dr., Potomac, MD 20854

It is postulated that ocean ring eddies produce hydrodynamic dipoles whose velocity fluctuations contribute to ambient noise. Arctic Ocean ring eddies are studied to relate existing flow data to ambient noise models on a yearly basis. The angular velocity of the ring flow shows annular regions of solid body rotation, irrotational flow and turbulence with transitions determined by maximum velocity and the Rayleigh--Taylor instability criterion. In decay, this rotating system, acting under vertical shear, produces Couette flow yielding horizontal dipoles with wave numbers that correspond to acoustic frequencies of 20 to 50 Hz. Using a dipole model and an estimated mechanoacoustic conversion efficiency, noise source levels are computed for the rings. Then, by the Ross formula for noise levels and the eddy areal density measured in AIDJEX (1975--1976), predicted ambient noise agrees with the Buck and Rosser model for low and moderate noise levels. This mechanism complements other noise sources, especially during times of quiet wind and ice. [Work supported by ONT.]