7.5
Wave-turbulence interactions in a breaking mountain wave
Craig C. Epifanio, Texas A&M University, College Station, TX; and T. Qian
The mean and turbulent structures in a breaking mountain wave are considered through an ensemble of high-resolution (essentially LES) wave-breaking calculations. Three aspects of the problem are addressed in particular:
(i) The production of turbulent kinetic energy (TKE) is considered and shown to be dominated by the shear generation and viscous dissipation. The shear production occurs along the upper edge of the lee-slope shooting flow, where the mean-flow Richardson number is persistently less than 0.25.
(ii) The turbulent fluxes of heat and momentum are computed and their role in shaping the wave-scale and larger-scale circulations is discussed. The most significant eddy effects stem from the tendency of the fluxes to decelerate the lee-side shooting flow. The resulting decelerative eddy forcing leads to a mean-flow Bernoulli loss, a cross-stream mean-flow PV flux, and a permanent upward transfer of mean-flow vorticity.
(iii) The dependence of the fluxes on the grid spacing is considered by computing a series of wave-breaking ensembles at varying resolution. Particular emphasis is given the net flux of mean-flow PV. With increased grid spacing the PV flux shifts from mostly resolved-scale to largely parameterized (as expected). For the lowest resolution case, the parameterization overestimates the PV flux by almost a factor of 2.
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Session 7, Mountain Waves and Obstacle flows
Tuesday, 7 August 2007, 4:00 PM-5:30 PM, Waterville Room
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