Energy transfer from high-shear, low-frequency internal waves to high-frequency waves near Kaena Ridge, Hawaii
Sun, Oliver M. T.
MetadataShow full item record
KeywordDiapycnal mixing; Energy transport; Internal waves; Nonlinear dynamics; Ship observations; Spectral analysis/models/distribution
Evidence is presented for the transfer of energy from low-frequency inertial–diurnal internal waves to high-frequency waves in the band between 6 cpd and the buoyancy frequency. This transfer links the most energetic waves in the spectrum, those receiving energy directly from the winds, barotropic tides, and parametric subharmonic instability, with those most directly involved in the breaking process. Transfer estimates are based on month-long records of ocean velocity and temperature obtained continuously over 80–800 m from the research platform (R/P) Floating Instrument Platform (FLIP) in the Hawaii Ocean Mixing Experiment (HOME) Nearfield (2002) and Farfield (2001) experiments, in Hawaiian waters. Triple correlations between low-frequency vertical shears and high-frequency Reynolds stresses, uiw∂Ui/∂z, are used to estimate energy transfers. These are supported by bispectral analysis, which show significant energy transfers to pairs of waves with nearly identical frequency. Wavenumber bispectra indicate that the vertical scales of the high-frequency waves are unequal, with one wave of comparable scale to that of the low-frequency parent and the other of much longer scale. The scales of the high-frequency waves contrast with the classical pictures of induced diffusion and elastic scattering interactions and violates the scale-separation assumption of eikonal models of interaction. The possibility that the observed waves are Doppler shifted from intrinsic frequencies near f or N is explored. Peak transfer rates in the Nearfield, an energetic tidal conversion site, are on the order of 2 × 10−7 W kg−1 and are of similar magnitude to estimates of turbulent dissipation that were made near the ridge during HOME. Transfer rates in the Farfield are found to be about half the Nearfield values.
Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 1524–1547, doi:10.1175/JPO-D-11-0117.1.
Showing items related by title, author, creator and subject.
On the interpretation of energy and energy fluxes of nonlinear internal waves : an example from Massachusetts Bay Scotti, Alberto; Beardsley, Robert C.; Butman, Bradford (Cambridge University Press, 2006-08-09)A self-consistent formalism to estimate baroclinic energy densities and fluxes resulting from the propagation of internal waves of arbitrary amplitude is derived using the concept of available potential energy. The method ...
Duda, Timothy F.; Rainville, Luc (American Geophysical Union, 2008-03-25)Barotropic (surface) and baroclinic (internal) tides were measured at four mooring sites during a field investigation of acoustic propagation characteristics and physical oceanography in the northern South China Sea. The ...
Subharmonic energy transfer from the semidiurnal internal tide to near-diurnal motions over Kaena Ridge, Hawaii Sun, Oliver M. T.; Pinkel, Robert (American Meteorological Society, 2013-04)Nonlinear energy transfers from the semidiurnal internal tide to high-mode, near-diurnal motions are documented near Kaena Ridge, Hawaii, an energetic generation site for the baroclinic tide. Data were collected aboard the ...