Numerical Sensitivity Experiments of Varying Model Physics on the Structure, Evolution and Dynamics of Two Mesoscale Convective Systems

Abstract

Abstract The effects of different model physics and different convective and boundary layer parameterization schemes are investigated using an 18-h nested-grid numerical simulation of the mesoscale convective systems (MCSs) that were responsible for the 19-20 July 1977 Johnstown flood. It is found that convective and resolable-scale diabatic process play crucial yet very different roles in the development and evolution of the MCSs. In particular, latent heat release resulted in development of strong vertical circulations, generation of an upper-level jet streak, formation of pronounced mesoβ-scale surface pressure perturbations, and rapid amplification of the traveling mesoα-scale wave that helped initiate the condensation processes. Resolvable-scale condensations appear to be directly responsible for the generation of a warm-core mesovortex and indirectly for a mesoscale convective complex (MCC). Without resolvable-scale heating, the model only reproduces the propagation of a squall line. Incorporation o...