Implementation of Hybrid En-3DVAR Assimilation Scheme in Rapid Cycling Assimilation System

A hybrid En-3DVAR (ensemble-three-dimensional variational data assimilation) was constructed based on the rapid refresh multi-scale analysis and prediction system–short term (RMAPS-ST) and the RMAPS-ensemble (RMAPS-EN) at Beijing Meteorological Bureau. The hybrid and 3DVAR schemes were conducted in the cold run and cycle run settings based on RMAPS-ST. The authors obtained the following conclusions: The single observation test showed that there was a good correspondence distribution between the hybrid data analysis (DA) increment and the ensemble spread. The hybrid DA-increment exhibited flow-dependent characteristics in both cold run and cycle run, but the 3DVAR DA-increment was isotropic. A rainfall case study revealed that the hybrid and 3DVAR had almost the same influence on the precipitation in the cold run setting, but the hybrid scores were significantly higher than those of the 3DVAR in the cycle run setting. The analysis of the ensemble spread and background error showed that they were better correlated in the cycle run than in the cold run.