Utilization of spectral bin microphysics and bulk parameterization schemes to simulate the cloud structure and precipitation in a mesoscale rain event

Sea breeze convection in Florida on 27 July 1991, accompanied by squall line formation, was simulated using MM5 with various microphysical schemes, including the Hebrew University spectral (bin) microphysics (SBM) and three recently developed bulk model parameterizations. The bulk schemes are the Seifert fall two-moment scheme (FTMS), the Reisner-Thompson two-moment ice scheme (TMS), and the Thompson two-moment ice scheme. The results were evaluated using observed rainfall and radar reflectivity, including radar derived contour frequency with altitude diagrams (CFAD). The SBM simulated quite well the time evolution of average and maximum rainfall amounts. A comparison of a CFAD derived from observations and CFADs derived from model calculated radar reflectivity suggests that the SBM simulates the three-dimensional structure of squall line convection and stratiform mixed phase cloud more realistically than the bulk parameterization schemes. However, the Thompson scheme shows a qualitative improvement over the other bulk parameterization schemes in the simulation of the three-dimensional structure of the squall line as indicated by comparison of its CFAD with the observed. All of the new bulk models simulate precipitation better than the earlier bulk parameterization schemes, but each still produces too much precipitation during too short periods of time and underestimates the area covered by stratiform clouds.