Internal solitary waves with acoustic applications to the Canadian Arctic and the Scotian shelf

Abstract

A joint Canadian and Japanese scientific experiment took place from 21 April to 25 May 1992 in Resolute Passage, Northwestern Territories. It gave an opportunity to deploy an acoustic Doppler current profiler (ADCP) on a very stable platform, the land fast ice, and provided the possibility to examine the current regime in three dimensions. It was found that the mean flow of the current in Resolute Passage was small and that the flow was dominated by tidal forcing. The diurnal and semi-diurnal constituents of the tide were found to be the most energetic and the tidal energy was aligned with the orientation of Resolute Passage. High frequency fluctuations of large amplitude were also found in all three components of the velocity field. A model based on the Korteweg deVries equation shows that many of those events are actually solitary waves. The influence of solitary waves on acoustic propagation is investigated both for the Arctic and for the Scotian Shelf. Acoustic modelling shows that, in Resolute Passage, the presence of a solitary wave in the water column had very limited effects on the sound propagation due to the small vertical sound velocity gradients. However, it was found that on the Scotian Shelf, where the sound velocity profile of the undisturbed water is not constant with depth thus allowing for more than one propagation path. The presence of solitary waves on the Scotian Shelf had a dramatic influence on the sound propagation in the water.