A Numerical Simulation of Nocturnal Drainage Flow

A three-dimensional mesoscale atmospheric model , previously used to simulate airflow over cooling ponds and hypothetical, simplified mountains , has been modified to simulate development of nocturnal drainage flow in realistic terrain, part of the California Geysers area. Turbulent fluxes appearing in the governing equations for mean variables are computed from simplified second-moment turbulence-closure equations where only a turbulence energy equation and a master-length scale equation are solved prognostically. Qualitative simulation of drainage flow, horizontal covergence in the valley, and resulting vertical motions are satisfactory. Simulated wind speeds near the surface are greater than observed values , possibly due to inadequate resolution of observations or to a lack of consideration of the drag associated with canopy flow.

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