Radar-reflectivity assimilation via diabatic DFI in the RUC

Stan Benjamin



As part of the 2007 RUC change package, an effective technique has been developed for assimilating 3-d radar reflectivity data hourly into the RUC. The key aspect of the design is specification of 3-d latent heating, replacing latent heating from both convective and explicit precipitation processes, within the diabatic forward step of the 20-min DFI used in the RUC model. The treatment of the radar reflectivity data both within the RUC 3dvar (used primarily for QC consistency with GOES and background), and subsequently, within the RUC model (including DFI), will be described. The assimilation of 3-d radar reflectivity provides a clear improvement both in forecast reflectivity and QPF at 3h but is also evident out to 12h. Case studies and overall verification statistics illustrating this improvement will be presented. This assimilation technique adds virtually no additional computational run time, and projects onto the entire physical parameterization suite. Although demonstrated here with the RUC, the generality of the approach is also fully applicable to other models including the ARW or NMM.