Impact of Additional Assimilation of Dual-Polarimetric Parameters: Analysis and Forecasts in a Real Case

The purpose of this study is to investigate the impact of assimilating dual-polarimetric parameters, i.e. differential reflectivity (ZDR) and specific differential phase (KDP), in addition to reflectivity (ZH) and radial wind (Vr) in a severe weather system. A squall line case forced by the synoptic southwesterly wind is selected to conduct the assimilation experiments. Besides, different microphysics parameterization schemes, including GCE, MOR, WSM6 and WDM6, are examined in the experiments. The results of the analysis field show that assimilating additional ZDR with single moment schemes (GCE and WSM6) can capture better mean raindrop size, yet it deteriorates the intensity of simulated ZH and KDP. Differ from GCE and WSM6, assimilating additional ZDR with double moment schemes (MOR and WDM6) would not lead to significant deterioration in the simulated ZH and KDP since the prognostic hydrometeor variables in double moment schemes include both mixing ratio and total number concentration. There will be more flexibility in adjusting microphysical states with two independent prognostic hydrometeor variables. The results of the short-term quantitative precipitation forecast (QPF) show that assimilating additional dual-polarimetric parameters with either single or double moment schemes increases the maximum of accumulated rainfall and the probability of heavy rainfall. In conclusion, double moment schemes can make better use of the extra information from dual-polarimetric parameters; furthermore, assimilating additional dual-polarimetric parameters, even with single moment schemes, can improve the performance of QPF, especially heavy rainfall events.