On the Mechanisms of Rain Formation in a Simulation of an Idealized Supercell
The two-moment Morrison microphysics scheme is modified to include three rain classes representing raindrops formed by warm processes, melting, and shedding. A high-resolution simulation of an idealized supercell storm is performed with the standard Morrison scheme and is compared to one using the modified “RainClass” scheme. Results show that rain originating from melted ice dominates the mass of the rain field at low levels. However, preferred regions of warm rain are found along the rear flank, and preferred regions of shed rain are found in the left forward flank. DSDs from the individual rain categories at a given location may be substantially different, leading to a total combined DSD not well modeled by an inverse exponential function. Despite the increased complexity of the rain field, however, the simulated DSDs still have smaller variability than observed. This suggests that the model is still too rigid in its treatment of rain DSDs. These and other results will be discussed.