径向风和反射率直接同化对一次梅雨锋暴雨模拟的影响

Impact of Direct Assimilation of Radial Velocity and Reflectivity on Simulation of a Meiyu Front Heavy Rain Case

利用中尺度数值模式WRF及其三维变分同化系统,采用NCEP再分析资料和合肥新一代天气雷达资料,针对2003年7月4—5日发生在江淮流域的一次梅雨锋暴雨过程,分析了直接同化雷达径向风和反射率对降雨模拟的影响。结果表明:1)直接同化雷达径向风能够改进低层辐合带的位置、增加低层气旋性扰动,增强低空急流核;改进垂直速度有利于对流的发生和发展。2)直接同化反射率能改进模拟回波位置,小雨量级TS评分改进明显,约提高了0.15。3)不同的同化频率对同化结果都有正的贡献,每10分钟同化一次的结果略优于每半小时同化一次的结果;双线性插值和四点平均两种稀疏化方法对同化结果的影响差异不明显。4)同化雷达径向风或反射率,可明显提高小雨量级的TS评分,改善整个雨带的位置,提高强降水中心预报的落区与量级。

The impact of direct assimilation of radar radial velocity and reflectivity was analyzed on the simulation of the heavy rainfall case in the Meiyu front occurred at Yangtze river during 4—5 July 2003 by the mesoscale numerical model WRF and 3DVAR system using NCEP reanalysis data and New-Generation Weather Radar data in Hefei.The results are as following：（1） the direct assimilation radial velocity can improve the position of low level convergence zone,increase low level cyclonic disturbance and enhance low level jet stream core.The improvement of vertical velocity was favorable to trigger and develop the convection.（2） The threat scorer of light rain with assimilated reflectivity was improved by 0.15 and the location of simulated reflectivity was closer to observation than the control experiment.（3） Both of the two different assimilated frequencies had the positive impact on the simulation of precipitation,but the impact of every 10 min was better than that of the every 30 min.The different impacts on forecast by the two thinning methods were not obvious.（4） The threat score of light rain was improved after the radar data had assimilated.At the same time,the location of rain belt was closer to that observed,and the forecast of the location and amplitude of severe precipitation center was improved.