Assimilation of multiple WSR-88D radar observations for short-term prediction of convective storms: a case study of the IHOP June 12-13 convective system

Recent studies have demonstrated the usefulness of radar observations in improving high-resolution model analysis and hence prediction of convective systems. These studies, although encouraging, have typically used observations from a single radar and performed in a very small domain for simulation of isolated thunderstorms. In this study, we extend previous studies to multiple Doppler radars and to larger convective systems. The convective system of June 12-13, 2002 observed during the International H2O Project (IHOP_2002) was used for the assimilation and prediction experiments. Radial velocity and reflectivity observations from four NEXRADs are assimilated into a convection-permitting numerical model using a 4D-Var system. Impact of the radar data assimilation is assessed by verifying the skill of subsequent very short-term (0-5 hours) forecasts.

From this case study, it is found that the 4D-Var radar data assimilation significantly reduces the model spin-up required in the experiments without radar data assimilation, resulting in significantly improved 5-hour forecasts. The impact of observations from each of the individual radar is examined by conducting a set of experiments in which data from each radar are alternately excluded. It is found that the mesoscale flow structure obtained from the radars surrounding the initial convective cells play an important role in successfully predicting the convective system.