一次局地大暴雨的地面观测资料同化预报试验研究

基于WRF（Weather Research and Forecasting）模式及其3DVAR（3-Dimentional Variational）资料同化系统，采用36 km、12 km 、4 km三层嵌套网格进行逐3 h资料同化和快速更新循环预报，对2011年5月8日鲁中一次局地大暴雨过程进行了资料同化敏感性试验。试验结果表明，地面观测资料同化和快速更新循环对本次降水的预报起到了关键性作用。在快速更新循环预报时不同化地面观测资料，或同化全部观测资料进行冷启动预报，模式均不能预报出山东的降水。同化地面观测资料后，显著改进了模式降水落区预报。地面观测资料同化可以影响到700 hPa高度以上温压湿风要素的变化，从而改变了大气初始场的温湿结构，导致模式预报的700 hPa附近高空大气湿度和热力不稳定增强，700 hPa以下低层风场更强，850 hPa鲁中以南风速较无观测资料同化的偏强2～4 m·s-1，低层风场的动力作用触发高空的不稳定大气，降水出现在山东。

Numerical study of surface data assimilation to a local torrential rain forecast

Using the WRF (Weather Research and Forecasting) model and its 3DVAR (3-Dimentional Variational) data assimilation system, data assimilation sensitivity experiments on a local torrential rain event in middle Shandong on 8 May 2011 are carried out adopting data assimilation and rapid update cycle of 36 km, 12 km and 4 km nested grid at three-hour intervals. Results show that both surface data assimilation and rapid update cycle are playing key roles in the precipitation forecast. During rapid update cycle, the model cannot forecast the rainfall in Shandong if assimilating no surface observational data or assimilating all surface observational data with cold start. The rainfall area forecast is significantly improved due to surface data assimilation, which can influence the atmospheric elements such as temperature, pressure, humidity, and wind over 700 hPa. Therefore, the temperature and humidity structure of initial atmospheric conditions is altered, the upper humidity and thermal instability are enhanced at around 700 hPa, the lower wind field becomes stronger under 700 hPa, the wind speed is 2 to 4 m·s-1 stronger than that without data assimilation at 850 hPa to the south of middle Shandong, and the upper unstable atmosphere is triggered by the dynamic effect of the lower wind field. As a result, the rainfall appears in Shandong.