雷达资料同化对江西东北部一次弓形回波过程模拟的影响

Influence of Radar Data Assimilation on Simulating a Bow Echo Happened in the Northeast of Jiangxi Province

利用雷达观测资料和FNL1°×1°再分析资料,采用中尺度WRF模式及其3DVar同化系统,探讨了同化多普勒雷达径向速度和反射率因子对2016年4月3日出现在江西景德镇的一次弓形回波过程模拟的改进效果及其影响途径。结果表明:1)只同化雷达径向速度或反射率因子均能改进模式对弓形回波的模拟效果,但同化雷达径向速度改进效果更好;同时同化两种资料改进效果最佳。2)雷达径向速度同化通过直接调整风场,进而引起水汽输送和水凝物凝结、凝华等微物理过程变化,对动力场和热力场都有一定调整;雷达反射率同化是首先将雷达反射率因子反演成雨水、雪和霰粒子混合比,能够调整水凝物场,但是当没有协调动力条件配合时,模式将不吸收这部分资料,对水汽场和动力场都没有明显改善;同时同化两种资料,能够综合调整动力场、热力场和水汽场,得到动力、热力和水汽协调的最优初始场。3)同化反射率资料只在积分初期模拟效果好,随着积分时间延长,ETS评分迅速降低;同化径向速度资料,积分初期效果不如同化反射率资料,但预报效果稳定;同时同化雷达反射率和径向速度模拟结果最好,在整个积分阶段ETS评分均为最高。

The radial velocity and reflectivity data from Doppler radars were assimilated by the Weather Research and Forecasting(WRF)model three-dimensional data assimilation(3DVar)system,and a bow echo happened in Jingdezhen was then simulated and studied by using the mesoscale model WRF.The main results were as follows:1)The simulations were both improved to some extent by the assimilation of radar radial velocity and reflectivity,but the radial velocity presented better performance,and the assimilation of both radar reflectivity and radial velocity assimilated exhibited the best result.2)Assimilation of radial velocity affected the wind field directly,and then affected the vapor transportation and microphysical processes such as coagulation and condensation of hydrometeor,which contributed to the adjustment of dynamic and thermal conditions.Assimilation of radar reflectivity retrieved rainwater,snow and graupel from radar reflectivity firstly,and then could adjust the hydrometeors fields.However,the model could not absorb these data due to lack of the dynamic field,and the dynamic and thermal conditions were not improved obviously.Assimilation of both the radar reflectivity and radial velocity could adjust the dynamic and thermal conditions synthetically to reach a best balance among dynamic,water vapor,and thermal conditions.3)Assimilation of radar reflectivity could improve the forecast skill only at the beginning of the simulation,as the simulation time went by,the equitable threat scores(ETS)decreased rapidly.Assimilation of radial velocity could make a stable improvement,although the simulated results were not better at the beginning than those reflectivity assimilation were.ETS maintained the highest throughout the integral time by the assimilation of both radar reflectivity and radial velocity and presented the best results.