Development and Research of GSI-Based Hybrid Ensemble-Variational Data Assimilation for Convection Resolving Regional Prediction Systems

A GSI-based EnVar data assimilation system is extended to directly assimilate both radar radial velocity and reflectivity to initialize convective-scale forecasts including isolated supercells and complex convectively active cases featured with multiple modes and interactions (Johnson et al. 2015; Wang and Wang 2016).  In this talk, progresses of further development and research of such system in the Warn On Forecast (WoF) context is first discussed. Because the 2-km grid spacing is not able to explicitly depict a tornado circulation, the GSI-based EnVar system is further developed with the dual resolution (DR)  capability where the analysis is produced a sub-kilometer resolution grid and the ensembles ingested by EnVar are still at relatively coarse resolution.  The newly developed dual-resolution EnVar system is examined on the 8 May tornadic supercell with a 2-km grid ensemble and a 500-m grid analysis. Our results show the DR system alleviates the southeast displacement of the vorticity swaths in the coarser 2km single resolution (SR) system. Our diagnostics indicate the better vorticity swaths in the DR system than the SR system result from more realistic rear and forward flank gust fronts.  Such more realistic gust fronts are due to the better analyzed size and location of the hydrometeors aloft. In addition to WoF, this system is also being developed and integrated with the prototype convection resolving HRRR and NAMRR systems assimilating multi-scale observations in collaboration with GSD and EMC.  The impact of using the GSI EnKF/EnVar to directly assimilate the radar data is being compared with the indirect cloud analysis approach which are currently implemented in HRRR and NAMRR.  These results are also planned to be presented in the conference.