The ERICA IOP 5 Storm. Part III: Mesoscale Cyclogenesis and Precipitation Parameterization

Modeling studies have consistently shown the importance of latent heat release in explosive marine cyclogenesis. However, a systematic evaluation of precipitation parameterization in the simulation of marine cyclones has been rare in the literature. This paper is the third in a series of modeling studies on the ERICA IOP 5 storm. The objective is to assess the performance of various subgrid-scale cumulus parameterization and resolvable-scale microphysics schemes in the simulation of the storm using the Penn State–NCAR mesoscale model MM5 at grid resolutions of 20 and 60 km. Emphasis is placed on the intensity, distribution, and character of precipitation and on the mesoscale low pressure centers embedded within the synoptic-scale cyclone. Principal findings are as follows. The distribution and intensity of precipitation, its partitioning into grid-resolvable and subgrid-scale portions, the atmospheric thermodynamic structure in the precipitation region, and the evolution of mesoscale low pressure centers were extremely sensitive to the choice of cumulus parameterization scheme. This is true for both the 20- and 60-km MM5. The partitioning of precipitation into subgrid scale and resolvable scale for a given convective parameterization is nearly the same for both the 20- and 60-km models. The detailed cold-cloud microphysics did not have a significant impact on cyclone deepening for tests carried out on the 20-km grid. The CAPE-based scheme developed by Kain and Fritsch gave the best simulation of this explosive marine cyclone on both the 60- and 20-km grids. This scheme effectively consumed the convective instability and captured the evolution of two observed mesolows. Analysis of the simulated mesolows showed that rapid intensification took place just in advance of a strong upper-level PV maximum. At low levels, the mesolows were characterized by large, diabatically produced PV maxima and by nearly coincident rainfall maxima. A number of PV-rainfall maxima, less visible in the pressure field, with a spacing of 150 km along the cold front, were also simulated in the 20-km Kain–Fritsch experiment. The realism of these PV-rainfall maxima cannot be confirmed due to the lack of observations. Similar features with enhanced pressure signature were seen in the simulations with the Grell scheme and no-cumulus scheme. The number, intensity, and evolution of mesolows were highly variable in the 20-km simulations of this case with different convective parameterization schemes. The amount of mesoscale perturbation of the pressure fields appears to be inversely proportional to the percentage of convective rainfall, being the least in the Kuo scheme (with 90% convective rainfall) and the most in the scheme without subgrid-scale convective parameterization (0%). No mesolows were simulated in an experiment that excluded latent heat release.