Bispectra of Internal Tides and Parametric Subharmonic Instability
Abstract
Bispectral analysis of the nonlinear resonant interaction known as parametric subharmonic instability (PSI) for a coherence semidiurnal internal tide demonstrates the ability of the bispectrum to identify and quantify the transfer rate. Assuming that the interaction is confined to a vertical plane, energy equations transform in such a way that nonlinear terms become the thirdmoment spectral quantity known as the bispectrum. Bispectral transfer rates computed on PSI in an idealized, fullynonlinear, nonhydrostatic Boussinesq model compare well to model growth rates of daughter waves. Bispectra also identify the nonlinear terms responsible for energy transfer. Using resonance conditions for an M2 tide, the locus of PSI wavenumber triads is determined as a function of parentwave frequency and wavenumbers, latitude and range of daughterwave frequencies. The locus is used to determine the expected bispectral signal of PSI in wavenumber space. Bispectra computed using velocity profiles from the HOME experiment are relatively noisy and the signal inconclusive.
 Publication:

arXiv eprints
 Pub Date:
 October 2014
 arXiv:
 arXiv:1410.0926
 Bibcode:
 2014arXiv1410.0926F
 Keywords:

 Physics  Atmospheric and Oceanic Physics