Editorial Type:
Article
Article Type:
Research Article

Revisiting Oceanic Acoustic Gravity Surface Waves

Jerome A. Smith Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California

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Print Publication:
01 Dec 2015
DOI:
https://doi.org/10.1175/JPO-D-14-0256.1
Page(s):
2953–2958
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Abstract

The reintroduction of compressibility into the equations for surface gravity waves can permit mixed acoustic–gravity modes that are periodic in the vertical as well as horizontal directions. These modes interact with the bottom even in deep water, so bottom motion can excite them. Because they propagate rapidly, it has been suggested they may be useful as precursors of tsunamis. Here the equations are revisited, and, using some robust approximations, some physical understanding and interpretation of the phenomena are presented. It is posed that these new modes can alternatively be thought of as acoustic modes slightly modified by a gravity wave boundary condition at the surface, rather than as surface waves dramatically modified by compressibility. Their potential use is not diminished; indeed, this alternative perspective should help make implementation more practical.

Denotes Open Access content.

Corresponding author address: Jerome A. Smith, Scripps Institution of Oceanography, University of California, San Diego, 8851 Shellback Way, La Jolla, CA 92093. E-mail: jasmith@ucsd.edu

Abstract

The reintroduction of compressibility into the equations for surface gravity waves can permit mixed acoustic–gravity modes that are periodic in the vertical as well as horizontal directions. These modes interact with the bottom even in deep water, so bottom motion can excite them. Because they propagate rapidly, it has been suggested they may be useful as precursors of tsunamis. Here the equations are revisited, and, using some robust approximations, some physical understanding and interpretation of the phenomena are presented. It is posed that these new modes can alternatively be thought of as acoustic modes slightly modified by a gravity wave boundary condition at the surface, rather than as surface waves dramatically modified by compressibility. Their potential use is not diminished; indeed, this alternative perspective should help make implementation more practical.

Denotes Open Access content.

Corresponding author address: Jerome A. Smith, Scripps Institution of Oceanography, University of California, San Diego, 8851 Shellback Way, La Jolla, CA 92093. E-mail: jasmith@ucsd.edu
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