Recent Development of WRF 3/4D-Var Radar Data Assimilation and Case Studies

The three- and four-dimensional variational data assimilation system of Weather Research and Forecasting model (WRF 3/4D-Var) is further developed to assimilate radar observations. The new development includes the tangent-linear and adjoint models of a Kessler warm-rain scheme, the new control variables of cloud water, rainwater and vertical velocity and their error statistics, and an indirect assimilation scheme for radar reflectivity. The performance of the updated the WRF 3/4D-Var system was estimated with single observation experiments as well as real data tests on a convective case. The results indicate that the WRF 4D-Var system produces reasonable responses to radar observations. The WRF 4D-Var shows significant improvement over the 3D-Var. The improvement on precipitation forecast is attributed to improved cold pool analysis, its associated convergence, and mid-level temperature distribution.