Energy Sources and Supply Rates of the Internal Wave Continuum

Matthew H Alford, University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States and Arnaud Le Boyer, Scripps Institution of Oceanography, MPL, San Diego, CA, United States
The energy source for the internal wave continuum, traditionally modeled by the Garrett-Munk spectrum, has long been assumed to be internal tides and near-inertial waves losing energy via wave-wave interactions. The mesoscale field may be an additional source. The issue is of fundamental physical interest as well as of practical value, since the energy flux through the continuum is related to the resultant turbulence via the Gregg-Henyey-Polzin parameterization. Yet, recent work suggests that loss rates from the internal tide computed from altimetry, numerical models and theory may fall short of that needed to fuel the continuum. The loss rates from near-inertial waves and the mesoscale to the continuum are very poorly constrained, but their relationship to parameterized mixing appears to depend on near-inertial-wave/mesoscale interaction. In this talk we first review the extant evidence of the relationships between internal tides, near-inertial waves, the mesoscale and the internal wave continuum. Then employing a database of about 2500 historical moored current meter records, we compute the time variation of the continuum and mesoscale levels and the near-inertial and tidal peaks, in order to examine the co-variation, and its spatial patterns, of each quantity. The level of the continuum varies by a factor of 3-10 in time and space (in contrast to the traditional view that it is constant), and is at certain locations correlated with variability in each potential source. Implications are discussed.