Assimilation of Doppler radar observations with an ensemble square root filter：A squall line case study

The effectiveness of using an Ensemble Square Root Filter (EnSRF) to assimilate real Doppler radar observations is investigated by applying the technique to a case of squall line occurred on 12 July 2005 in the midwestern part of Shandong Province as done by the Weather Research and Forecasting (WRF) model. The experimental results show that, (1) the EnSRF system has the ability to effectively assimilate Doppler radar data: since the information at convective scale is added into the numerical model through radar data assimilation the analyzed field is improved noticeably, the model spin-up time is shortened, and the surface precipitation forecast is improved correspondingly; (2) compared with the forecast of control run, the forecast initiated from the EnSRF analysis can give a more accurate prediction of the microphysical field, and the predicted wind field and thermal field are reasonable and they are in accordance with the characteristic of convective storm; (3) the propagation direction of the squall line forecasted by the ensemble mean analysis is consistent with observations, but the propagation speed is faster than observed speed, because of the nonlinear development of the convective storm, the period of validity of forecast is about 5 to 6 hours.