Research On Assimilation Of Weather Radar Data For Hail Process

Accurate prediction of catastrophic weather such as hailstorm is very important for people's production and life.With the development of numerical weather forecasting models,data such as radar observations and satellite observations can be assimilated into the models to adjust the initial field conditions to achieve the purpose of improving weather forecasting.The WRF(Weather Research and Forecast)model threedimensional variational data assimilation system and radar data assimilation method based on the system were used in the paper to simulate a hail weather process occurred in Bayannur,Mongolia,China,on August 9,2019(UTC).The Doppler weather radar observations(CINRAD/CD radar)is used for the WRF model simulation and data assimilation.The characteristics of this hailstorm process are analyzed based on the observational realities of the Doppler weather radar in this article.According to the results of analysis,the P3-50(Morrison and Milbrandt)parameterization scheme is selected to simulate the weather process.In order to evaluate the improvement effect of the Doppler weather radar data assimilation method on the initial field,wind field,radar echo and other aspects of the hail weather process and the influence of the weather process forecast results,two sets of comparative tests are designed: 1)control test(CTL):only WRF model simulation without data assimilation;2)assimilation test(DA):Doppler weather radar reflectivity and radial wind data were simultaneously cyclically assimilated.The results show as follows: 1)when the hailstorm is coming,there are obvious V-shaped notches on the radar echo figure(CAPPI),and the echo intensity can reach 50-60 d BZ,which can be used as a hail warning indicator;2)The P3-50 parameterization scheme has the identification of the ice phase category of the particles(such as ice,snow and graupel)which can better simulate the hail weather process,but the results of the model simulation still deviate from the results of the actual radar observations;3)The initial field conditions can be adjusted after assimilation of radar data.The gradient of the pressure field was enhanced in the assimilation test(DA),the isobars became denser and a low-pressure system corresponding to convective weather was appeared in the sea level pressure field.What's more,the CAPE value increased first then decrease which means the occurrence and end of the hail process;4)The simulated echo intensity was increased to reach the hail echo intensity in the assimilation test,but the simulated echo position was biased,the improvement effect after data assimilation is maintained within 6 hours;5)The wind field was effectively improved by radar data assimilation,after the assimilation test,the simulated wind field at 700 h Pa and 500 h Pa height has strong wind speed shear,and the wind direction has obvious cyclonic shear;6)Compared with the control experiment,data assimilation had a certain improvement in precipitation forecast,but the effect was not significant.In the area where hail occured,the radar echo was strong and the simulated precipitation was much larger than the actual observation value,especially after 6 hours,the forecast results greatly deviated from the actual precipitation value.