Exploring the Nam's Fully Cycled Hybrid Variational-EnKF Data Assimilation System for High Impact Weather Systems

A convection-allowing, GSI-based hybrid Variational-EnKF data assimilation system in a development-version of the NAM framework is being explored using regional ensembles cycled by the EnKF subsystem and direct assimilation of radar reflectivity. To attain such a goal, various strategies and schemes mainly leveraging the continually progressing GSI are explored on the basis of recent experiences/progresses at EMC in this respect. The compromise between the computation burden and the benefit of the increased ensemble sizes are investigated with quantitative analysis of the required computational resources for various parts of the whole system. The real case performance of this system and lessons learned will be reported.