Development of an EnKF/hybrid data assimilation system for mesoscale application with the Rapid Refresh

NOAA's Rapid Refresh system (RAP) is an hourly-updated regional data-assimilation and forecasting system that uses the Weather Research and Forecasting (WRF-ARW) model with 13-km horizontal grid spacing and the Gridpoint Statistical Interpolation (GSI) analysis package. Numerous and varied observations are assimilated into the RAP using a 3DVAR method within the GSI. Development and testing work on an EnKF / hybrid data assimilation system for use with the RAP is ongoing. Initial coordinated work with a 40-km coarse resolution system by colleagues at the Center for Analysis and Prediction of Storms (CAPS) has yielded encouraging results. More recent tests have been completed with a 13-km version of the system. Preliminary analysis of the results indicates that the spread among ensemble members is too small. Efforts to refine the methodology to address this issue are ongoing. Additional work will also examine dual-resolution options. In this talk, we will describe our ongoing EnKF / hybrid data assimilation work, including current configurations of the EnKF and hybrid systems, results obtained so far and issues encountered. The results of retrospective EnKF / hybrid data assimilation experiments will be compared with the 3DAR-based operation system. Plans for future work will be discussed, as well as steps toward operational implementation of an ensemble-based data assimilation system for the RAP.