Resonant Internal Wave Interactions

Abstract

INTERNAL waves in the ocean are of critical importance both to the large scale oceanic energy and momentum balance and to smaller scale oceanic processes. Most discussions of the physics of these waves concentrate on linear waves of infinitesimal amplitude; however, both the breaking of internal waves and the generation and decay of their oceanic spectra involve nonlinear processes. We describe here the preliminary results of an experimental and theoretical investigation of the effects of non-linearity on a resonant pair of discrete internal waves. The only other resonant interaction experiments known to the authors are (1) careful definitive measurements of initial trends for a very weak third-order surface gravity wave interaction¹, and (2) experiments which relate an instability of internal gravity waves in a two-fluid system to a theorized second-order resonance². Our objective was to generate two waves theoretically capable of resonant interactions and to show, by measuring elementary definitive properties, that a second-order resonance does, in fact, occur in the fluid.