On the underwater sound generated by the counterpropagating sea-surface wave

Abstract

Two counterpropagating gravity-capillary waves of the same frequency, forming a standing wave on the sea surface, give rise to a sound wave traveling away from the surface [M. S. Longuet-Higgins (1950); L. M. Brekhovskikh (1966)]. The effect can be described in terms of three-wave nonlinear interaction [V. V. Goncharov, K. A. Naugolnykh, and S. A. Rybak (1977)]. The frequency and the wave number of the radiated wave are determined by the synchronism conditions. The surface waves propagating in the opposite directions can be generated by the action of the wind on the remaining swell of a cyclone or due to nonlinear interaction of the gravity-capillary waves. The progressive gravity-capillary waves superimposed on the flow produced by the finite-amplitude dominant gravity wave can be blocked at the points where its group velocity balance the convection by the larger-scale flow generating the reflected wave. As a result in the field of progressive waves produced by wind the counterpropagating wave appears generating the sound. [Work partially supported by Collaborative Linkage Grant No. 977 890.]