Search

Internal gravity waves of tidal frequency are generated as the ocean tides push water upward onto the continental shelf. Such waves also arrive at the continental slope from deep water and are heavily modified by the change in water depth. The wave generation and wave shoaling effects have an additional level of complexity where a canyon is sliced into the continental slope. Recently, steps have been taken to simulate internal tides in canyons, to understand the physical processes of internal tides in canyons, and also to compute the ramifications on sound propagation in and near the canyons. Internal tides generated in canyons can exhibit directionality, with the directionality being consistent with an interesting multiple-scattering effect. The directionality imparts a pattern to the sound-speed anomaly field affecting propagation. The directionality also means that short nonlinear internal waves, which have specific strong effects on sound, can have interesting patterns near the canyons. In addition to the directionality of internal tides radiated from canyons, the internal tide energy within the canyons can be patchy and may unevenly affect sound.

Studies using idealized bathymetry have shown that steep slopes can have important effects on the geometric structure of ocean sound fields. Other studies have provided insight into the temporal variability of sound fields in the moving ocean. There is a general understanding that both effects occur together in the ocean, but their relative importance is not fully known, nor is the way they interact. The processes are often linked because slopes can generate strong internal tides and waves. Here, the coupled spatial and temporal variability is investigated using time-stepped three-dimensional (3.5-D) sound propagation modeling. The needed ocean sound-speed information is generated using modern regional ocean modeling. Solutions of the 3D parabolic acoustic wave equation are generated for a few hundred hertz. The spatial patterns of sound reveal that temporal intensity variation (scintillation) caused by internal tides can be enhanced at areas where sound encounters steep slopes. The magnitude of the effec...