雷达资料同化频次对一次西南涡暴雨的影响试验

Influence of Frequency Assimilation with Radar Data in Southwest Vortex Rainstorm

利用ARPS模式的三维变分同化系统ARPS-3DVAR和复杂云分析方案,采用重庆多普勒天气雷达资料,对一次西南涡暴雨过程进行了影响试验,分析雷达资料同化及其同化频次对初始场的改善情况以及对此次暴雨预报结果的影响。结果表明:(1)同化雷达资料后,模式初始场较好地刻画出回波的强中心和大致分布,增加了中小尺度天气系统的信息,多次循环同化试验强降水区存在β中尺度气旋性涡旋,配合低层强辐合,增强上升运动和西南涡的发展。(2)在预报场,同化雷达资料后改善了预报前期没有降水的情况,18 min同化试验的降水预报效果最好,且其TS评分也最高,其次是12min、6 min、单次同化和24 min同化间隔试验方案。(3)最大垂直速度在连续同化后预报的第18 min达到最大,表明ARPS模式需要18 min来调整模式变量之间的动力与热力约束以达到平衡状态,更长或更短的同化间隔都会有负影响,这也是18 min同化间隔试验的雷达回波和降水预报效果最好且TS评分最高的可能原因。

In order to analyze the effect of rainfall forecast and initial field with the radar data assimilation and different assimilating intermittence in the Southwest Vortex rainstorm process,this paper illustrates the single time and multiple times cycle assimilating experiments in the southwest vortex rainstorm process on 21 July 2012 by assimilating the Chongqing Doppler radar data with the three-dimensional variable data assimilation system( ARPS- 3DVAR) and complex cloud analysis scheme of the ARPS model. The result showthat:( 1) Assimilating radar data,model initial field depict the strong center and distribution of the echo,increasing the meso-and micro-scale systems information. Multiple times cycle assimilation experiments have β meso-scale cyclonic vortex,and work with the lower layer convergence,it enhances the ascending motion and develops the southwest vortex.( 2) In prediction field,it greatly improve the situation that no rainfall at the period forecast after assimilating radar data. The 18 min assimilation intermittence experiment does the best rainfall forecast and gets the highest score,as is followed by 12 min,6 min,single time and 24 min assimilation experiment.( 3) The maximum vertical velocity reach maximum value by forecasting 18 min after continues assimilating,it shows that the model takes 18 minutes to adjust a suitable dynamic and thermodynamic constrains among different variables and to achieve a balance condition. When cycle assimilation is shorter or longer than 18 minutes,the mode will be badly effect. This may be the reason why the 18 min assimilation experiment have a better forecast of the rainfall and the highest TS score.