The mesoscale model chosen to conduct this study was the Regional Atmospheric Modeling System (RAMS) developed at Colorado State University. A single grid with 1 km grid spacing in the horizontal and variable spacing in the vertical was used. The model was horizontally homogeneously initialized using a sounding that is representative of severe storm days over Oklahoma. A warm, moist bubble was used to initiate convection. The bulk microphysical species include vapor, cloud droplets, rain, pristine ice, snow, aggregates, graupel and hail. The simulations were run out for two hours.
Several tests have been conducted to evaluate the sensitivity of supercell storm dynamics to the type of microphysical scheme used, to variations in the mean hail and rain diameters, and to the exclusion of ice processes. Within most microphysical parameterization schemes, several parameters are assigned values somewhat arbitrarily as a result of the lack of microphysical measurements for many storm systems. One such parameter is the mean diameter of a species. In the first series of tests, simulations were performed in which the mean hail diameter was varied from 3mm to 4cm, and the mean rain diameter from 1mm to 5mm. In the second series of tests, all ice processes were turned off in order to evaluate the effect of excluding ice species. Finally, it is sometimes argued that the more complicated a parameterization scheme, the better the scheme performs. The two-moment microphysical scheme was used in place of the single-moment scheme in the third series of tests to assess the validity of this hypothesis. The results of these sensitivity tests show significant effects on numerous aspects of supercell storm dynamics. These results will be presented.