Comparison of different momentum control variables on assimilating radar observations for the forecasts of a dispersive convective event

In this study, the effects of background error covariance (BE) using stream function ψ and unbalanced velocity potential χ u as momentum control variables (CV5 scheme) BE U V (CV7 on assimilating radar radial reflectivity data for short-term forecasts dispersive convection in a weak environmental field are explored based weather research forecasting model (WRF) its 3DVAR assimilation system. The 4 km resolution forecast samples generated to formulate CV5 CV7 by National Meteorological Center (NMC) method. single-observation experiments reveal that differences between two statistics mainly reflected variables. increment wind from shows more small-scale local characteristics. Comparing with experiment, real observation tests both improve precipitation forecasts. But scheme improves strong convective systems fields better than CV5. First, significantly suppresses spurious when compared scheme. addition, also reduces errors surface analysis is local. Further water vapor convergence conditions scheme, which may be reason performance subsequent