The spatial distribution of convective precipitation - An evaluation of cloud microphysics schemes with polarimetric radar observations

Abstract

The representation of cloud microphysics in numerical weather prediction models contributes significantly to the uncertainty of weather forecasts. Polarimetric radar observations are increasingly used to evaluate numerical weather simulations, due to their sensitivity to microphysical properties. Typically, this evaluation is performed for individual case studies, which limits the generalizability of the results. This is particularly problematic for convective precipitation events, which are characterized by high variability due to their small scale and rapid error growth of initial uncertainties, and are often associated with severe weather phenomena. In this study, the performance of microphysics schemes in the simulation of convective precipitation events is evaluated statistically over a 30 d dataset. The aim is to assess the distribution of precipitation into convective and stratiform regions, and the microphysical properties in these regions based on radar reflectivity and differential reflectivity. Within a Weather Research and Forecasting model setup, 5 different microphysics schemes of varying complexity are evaluated. The choice of microphysics schemes has a significant impact on the distribution of precipitation; the median convective area fraction varies by an order of magnitude between the microphysics schemes. These differences are attributed to differences in rain drop size distributions. In the convective core, the FSBM and Morrison schemes frequently lack large rain drops, while the Thompson and P3 schemes simulate too many. Statistical evaluations are important to address the prevailing uncertainty surrounding cloud microphysics. The framework presented in this study can serve as a guide for future statistical evaluations of weather models with polarimetric radar observations.