Evaluation of Convection and Precipitation Properties from Cloud-Resolving Modeling of a Squall Line Case with Different Microphysics Schemes

Cloud –resolving model (CRM) simulations of deep convection have a large spread. It is imperative to evaluate modeled convection properties including updraft velocity with observations to understand model or parameterization performances and guide the improvement of model or parameterization. A constrained model intercomparsion study on a mid-latitude mesoscale squall line is performed using the Weather Research & Forecasting (WRF) model at 1-km horizontal grid spacing with eight cloud microphysics schemes. Various observational data are employed to evaluate the simulated convective dynamics and precipitation by different microphysics scheme, including 3-D multi-Doppler retrieved wind fields, MESONET surface meteorological data, NEXRAD radar reflectivity, and a few precipitation products. We find that all simulations tend to produce a wider convective area but a much narrower stratiform area. The magnitudes of virtual potential temperature drop, pressure rise, and wind speed peak associated with the passage of the gust front are significantly smaller compared with the observations, suggesting simulated cool pools are weaker. Simulations generally overestimate the vertical velocity and radar reflectivity in convective cores compared with the retrievals, but some schemes do perform much better then other schemes. The reasons leading to the large spread are examined.