Abstract

This research focuses on assimilating radar data into a high-resolution NWP model to improve short-term quantitative precipitation prediction (QPF). The WRFDA-4DVAR (4-dimensional variational data assimilation system of Weather Research and Forecast model) was further developed to assimilate rada... Show moreThis research focuses on assimilating radar data into a high-resolution NWP model to improve short-term quantitative precipitation prediction (QPF). The WRFDA-4DVAR (4-dimensional variational data assimilation system of Weather Research and Forecast model) was further developed to assimilate radar reflectivity observations, and a convective case was carried out to assess the performance of the enhanced 4DVAR system. The development includes 1) the inclusion of cloud water and rain water as hydrometeor control variables and their modeling of error covariance; 2) the development of tangent-linear and adjoint of a Kessler warm-rain scheme; 3) a new observation operator for radar reflectivity. The updated WRFDA-4DVAR system was tested with a convective case occurred on June 13 2002 during IHOP_2002 (International H2O Project) experiment. The impact of radar reflectivity, along with radar radial wind, on analysis and short-term numerical prediction of the IHOP case were assessed. Compared to the control experiment from Eta model 40 km analysis and 3DVAR analysis, radar data assimilation with 4DVAR method initiated the convection system in the first hour and improved the hourly precipitation forecast skill. Assimilating the reflectivity and radial velocity observations in 4DVAR enhanced the moisture and produced a cooling region near the surface in the convective region, which helped to maintain the convective system. Show less