Joint Session J4.1 Parameterization of internal wave breaking due to near-inertial shear

Tuesday, 9 June 2009: 3:50 PM
Pinnacle BC (Stoweflake Resort and Confernce Center)
Julie C. Vanderhoff, Brigham Young University, Provo, UT

Presentation PDF (1.1 MB)

Internal waves are continuously being generated and propagating through the ocean and atmosphere. Internal wave breaking can occur far from generation sites, and the resultant mixing can transport momentum, heat, and pollutants across isopycnals, maintaining the energy balance in the ocean and preventing a stagnant deep ocean. But global circulation models cannot resolve these motions and they must be parameterized. For a completely accurate parameterization, all waves and their possible ensuing motions due to other waves, bottom topography, vortices, boundaries, etc. must be accounted for in the computations. Although many interactions are possible as internal waves propagate, evidence of constant large scale inertial motions in the ocean lead us to study the breaking of internal waves which propagate both aligned with and in opposition to large scale inertial waves. The results of the two types of interactions are dynamically different: one is a time-dependent critical level and the other a caustic interaction. These different types of interactions can lead to wave-breaking pre-or post-maturely due to the time-dependence of the inertial waves. The interaction is modeled through integration of the fully nonlinear, inviscid, Boussinesq equations of motion. In general, breaking is found to occur within a particular region of the inertial wave, which shifts for small scale waves that approach the interaction with different group velocities. Small-scale internal waves with the largest vertical wavelengths are most likely to break immediately as they enter an inertial wave propagating in the opposite direction, where the smallest vertical scale waves are more likely to break in-between strong refraction sites, if at all. When propagating the same direction, the scale separation between the waves is also important in determining breaking probability although in this case larger separation results in a higher probability of breaking. Wentzel-Kramers-Brillouin (WKB) ray tracing is used to supplement the fully nonlinear numerical model. These statistics expand the reach of calculations from the simulations and compare well with not only which waves are expected to break due to the time dependence, but also where they would be expected to break within the inertial wave, dependent on their properties. Results of the models also compare well with observations from the Hawaiian Ocean Mixing Experiment (HOME).
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