Monday, 30 August 2010: 1:30 PM
Alpine Ballroom A (Resort at Squaw Creek)
In two recent papers, the authors have reported on numerical simulations of conditionally unstable flows past an idealized mesoscale mountain ridge. These idealized simulations, which were performed with an explicitly resolving cloud model, allowed the investigation of the solution precipitation characteristics as a function of the prescribed environment. The numerical solutions were carried out for different uniform-wind U flowing past a bell-shaped ridge of height h and half-width a and using an idealized unstable sounding with prescribed Convective Available Potential Energy (CAPE), Downdraft CAPE (DCAPE), Level of Free Convection (LFC), tropopause height ht, and static stability N2. Dimensional analysis of the numerical solutions revealed that the simulated maximum nondimensional rainfall rate depends on five nondimensional parameters: h/LFC, h/a, (a/U)/( ht/ CAPE0.5), DCAPE0.5 /U and N LFC/U. In the present work we report on the application of these theoretical results to observed cases of orographically forced convective rainfall including cases of the Big Thompson Flood (1976, Colorado), the Oahu Flood (1974, Hawaii) and several others. Specifically we have carried out numerical simulations using observed and idealized soundings relevant to the observed cases but with idealized topography. We find that the observed conditions fit reasonably well within the theoretically derived parameter space for intense orographic convective rainfall.
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