6.1
Gravity wave instabilities at large and small amplitudes: competition between wave-wave interactions and wave breaking (Invited Speaker)
David C. Fritts, NorthWest Research Associates, Inc., Colorado Research Associates Division, Boulder, CO
Gravity waves exhibit a wave range of instabilities that span all wave amplitudes and intrinsic frequencies. Linear theory provides a useful guide to initial instability structures and growth rates, but fails to define finite-amplitude effects. Numerical studies indicate a competition between 2D and 3D dynamics across the amplitude spectrum. The primary instabilities at small amplitudes and high frequencies are 2D interactions transferring initial wave energy to gravity waves having smaller vertical scales and lower frequencies. At larger amplitudes, 3D dynamics predominate, but both 2D and 3D dynamics contribute to energy transfers. Wave breaking at larger amplitudes proceeds rapidly, and leads to large amplitude reductions and a broad inertial range of turbulence on time scales of ~ 1 – 2 wave periods. Turbulence is strongly correlated with the gravity wave phase, but is also highly variable in intensity and remains highly anisotropic throughout the evolution. As turbulence subsides, a quasi-2D motion field remains and dominates the variances and fluxes at late times. At smaller wave amplitudes, wave-wave interactions predominate, but localized breaking also occurs. Wave-wave interactions are also substantially enhanced when multiple waves have finite initial amplitudes.
Session 6, Gravity Wave Observations, Modeling and Parameterization
Thursday, 23 August 2007, 8:30 AM-12:00 PM, Multnomah
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