Radar Reflectivity Data Assimilation with the Four-Dimensional Variational System of the Weather Research and Forecast Model

The capability of radar reflectivity data assimilation was developed within the Weather Research and Forecast model (WRF) four-dimensional variational data assimilation system (WRFDA-4DVAR). The model prognostic variables of cloud water and rain water were used as new microphysical control variables. The tangent-linear and adjoint of a Kessler warm-rain scheme were developed and incorporated into WRF linear and adjoint models to propagate the perturbations of cloud water and rain water. The WRFDA-4DVAR system is tested with a convective case occurred on June 13 2002 during International H2O Project (IHOP_2002) experiment. The issues of “dry background” which means there is no rain in first guess but there is RF observation, and “dry observation” which means there is rain in first guess but no RF observation are well discussed. The impact of radar reflectivity, along with radar radial wind, on analysis and short-term numerical predictions of the IHOP case will be assessed.