OBSERVATIONS OF THE SWASH EXPRESSION OF FAR INFRAGRAVITY WAVE MOTIONS

Rob Holman, Peter Howd, Joan Oltman-Shay, Paul Komar

Abstract


One of the important results from the recent SUPERDUCK experiment was the discovery of very low frequency motions (10 -103 second periods) with anomalously short longshore wavelengths (102meters). Subsequent analysis showed the motions to be shear waves, unstable perturbations of the mean longshore current that act to conserve potential vorticity. A specific prediction of the model is that these waves have negligible elevation signal (they are non-divergent), in contrast to gravity waves. Examination of simultaneous run-up data confirms the non-divergent nature of the solutions. While edge wave modes were detected, no significant swash energy was seen in the low frequency, high wavenumber region where shear wave energy was found in the current meter data. This apparently negative result adds support to the interpretation of these motions as shear waves.

Keywords


infragravity waves; swash; swash observations

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