The Sensitivity of Numerically Simulated Cyclic Mesocyclogenesis to Variations in Model Physical and Computational Parameters

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Abstract
In a previous paper, a three-dimensional numerical model was used to study the evolution of successive mesocyclones produced by a single supercell storm, that is, cyclic mesocyclogenesis. Not all supercells, simulated or observed, exhibit this behavior, and few previous papers in the literature mention it. As a first step toward identifying and understanding the conditions needed to produce cyclic redevelopments within supercell updrafts, this paper examines the effect on cyclic mesocyclogenesis of variations in model physical and computational parameters. Specified changes in grid spacing, numerical diffusion, microphysics options, and the coefficient of surface friction are found to alter, in some cases dramatically, the number and duration of simulated mesocyclone cycles. For example, a decrease from 2.0 to 0.5 km in horizontal grid spacing transforms a nearly perfectly steady, noncycling supercell into one that exhibits three distinct mesocyclone cycles during the same time period. Decreasing... Abstract In a previous paper, a three-dimensional numerical model was used to study the evolution of successive mesocyclones produced by a single supercell storm, that is, cyclic mesocyclogenesis. Not all supercells, simulated or observed, exhibit this behavior, and few previous papers in the literature mention it. As a first step toward identifying and understanding the conditions needed to produce cyclic redevelopments within supercell updrafts, this paper examines the effect on cyclic mesocyclogenesis of variations in model physical and computational parameters. Specified changes in grid spacing, numerical diffusion, microphysics options, and the coefficient of surface friction are found to alter, in some cases dramatically, the number and duration of simulated mesocyclone cycles. For example, a decrease from 2.0 to 0.5 km in horizontal grid spacing transforms a nearly perfectly steady, noncycling supercell into one that exhibits three distinct mesocyclone cycles during the same time period. Decreasing...