Monday, 21 June 2004: 8:45 AM
Most previous numerical studies of mountain induced disturbances in stably stratified flow have relied on rather artificial flow initializations. In this paper, we explore the evolution and dissipation of three-dimensional disturbances induced by an isolated ridge in a simple, dynamically consistent, large-scale flow. At the initial time, a stagnant region of the large-scale wind perpendicular to the ridge (U) accelerates to 20 m/s and then decelerates back to zero over an interval of 50 hours. The large-scale static stability (N) is constant throughout the domain. The nonlinearity parameter e=Nh/U ranges from infinity to order unity and back to infinity over the roughly two-day period, or equivalently, over a mean cross-mountain advective time scale of 100.
The transition between highly nonlinear flow (high e) and the quasi-linear wave regime is discussed and compared with observations of tidal flow in Knight Inlet. The Doppler shifting of the mountain wave train and a tendency to develop breaking waves during the deceleration of the large-scale flow are also examined.
Wake vortices are produced in the high-e flow regimes at both the beginning and the end phases of the roughly two-day period. The structure and distribution of these lee vortices during each phase is, however, rather different due to the differences in both the sense of the mean-flow acceleration and to the presence of large-scale diffluence in the accelerating flow (or confluence in the decelerating flow.)
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