Physical initialization applied in WRF‐Var for assimilation of Doppler radar data

Abstract

WRF‐Var is further developed with Physical Initialization (PI) to assimilate Doppler radar radial velocity and reflectivity observations. In this updated 3D‐Var, specific humidity and vertical velocity are first derived from reflectivity with PI, and then the model fields of specific humidity are replaced by the modified ones, finally, the estimated vertical velocity is added to the cost‐function of the existing WRF‐Var (version 2.0) as a new observation type, and radial velocity observations are assimilated directly by the method afforded by WRF‐Var. It is tested with a rainfall event that occurred in Hubei province near the Yangtze River on 19 June 2002. Results show that the updated 3D‐Var shows better capability to forecast the precipitation than the WRF‐Var does, and the forecast reflectivity field correlates well with the observations for about 4‐h prediction period.