利用WRF和多普勒雷达资料同化对一次江淮地区梅雨降水过程的模拟研究

Research on the simulation of a precipitation event along the Meiyu Front in the Jianghuai area using WRF and Doppler Radar data assimilation

为了研究同化雷达资料对数值模式降水预报的改进效果,针对2015年6月26—28日江淮地区梅雨降水过程,进行了结合雷达资料同化的数值模拟研究。首先介绍了过程的降水概况、环流形势。其次,利用WRF模式进行降水过程的数值模拟,在完成控制试验的基础上进行WRF-3DVAR的雷达资料同化。经过15 h的启转后,分别进行了针对背景误差协方差矩阵中特征长度和方差尺度的敏感性试验,得到最适合本次个例的特征长度(0.5)、方差尺度(0.7)。设置最优的特征长度和方差尺度后,进行同时同化反射率因子与径向风、单独同化反射率因子和单独同化径向风的同化试验,并分别设置了间隔为1 h和30 min的同化频率。通过分析个例水汽场、动力场及降水预报场,得到如下结论:1)雷达数据同化能够有效提高降水预报效果;2)同时同化雷达反射率因子和径向风的效果最好;3)同化雷达资料频率越高,效果提高也越明显。

In order to study the improvements of the numerical weather forecast model with radar data assimilation on precipitation forecast,in this paper,an experiment is performed to simulate the Meiyu Front precipitation event during the period of June26—28,2015in the Jianghuai area.The precipitation features and synoptic situation of the event are described with emphasis on the evolution of mesoscale convective systems which contribute greatly to the rainfall.The WRF mode is applied to perform this simulation.After the control experiment,the3DVAR radar data assimilation scheme is executed.After15h spin-up,the sensitivity experiments for len_scaling and var_scaling of background error covariance matrix are performed respectively.The optimal len_scaling is0.5,and optimal var_scaling is0.7.By setting the optimal len,var and assimilation time-step of30min and1h,experiments of assimilating reflectivity factor,radial velocity individually and simultaneously are implemented.The results from the analyses on the water vapor,dynamic and precipitation fields reveal the following:1)assimilating radar data can effectively improve precipitation forecast,2)assimilating both radar reflectivity factor and radial velocity yields superior precipitation forecast,and3)higher frequency of assimilating radar data yields superior precipitation forecast.