Internal wave-wave interactions. Part I: The role of internal wave vertical divergence

Small-scale internal waves are numerically ray-traced through random 3D Garrett and Munk internal wave backgrounds. Past ray-tracing investigations of the transfer of internal wave energy toward small scales have considered only interactions with background vertical shear V-z = (U-z, V-z). Here, scale analysis and numerical simulations indicate a nonnegligible role for vertical divergence W-z. Background low-frequency vertical shear V-z transfers high-frequency test waves toward small scales while background vertical divergence W-t transfers low frequency test waves toward small scales. These ray-tracing results resemble those of weak resonant-triad interaction theory, although the interactions considered here are not limited to be weak or resonant.