中文摘要：

利用2015年6—8月GR APES-REPS（Global/RegionalAssimilation and Prediction System-Regional Ensemble·Prediction System）区域集合预报资料,并设计西南低涡格点资料客观识别方法对西南低涡中心位置进行定位,首先评估GRAPES控制预报对西南低涡的预报准确性,之后挑选出四次生命史较长的西南低涡过程,分析评估GRAPES-REPS对西南低涡发生、发展、移动及降水过程集合预报性能。结果表明：（1）GRAPES模式对西南低涡预报的命中率较高,空报率略大于漏报率。（2）GRAPES-REPS对西南低涡发生和发展的预报效果较好,绝大部分集合预报成员能预报西南低涡发生和发展过程,但对西南低涡发生时间预报总体偏早。（3）GRAPES-REPS对西南低涡移动路径在24 h预报时效内比较合理,且集合预报平均明显优于控制预报,24 h之后东移型西南低涡移动路径明显偏北。（4）GRAPES-REPS对西南低涡强度预报总体偏强,表现为中心正涡度值偏大,位势高度值偏低。（5）24 h预报时效内,西南低涡触发的小雨到大雨量级的降水概率评分均有较好表现,且落区与实况接近,而暴雨落区个别略有偏北,但基本吻合。24 h之后,由于东移型西南低涡移动路径偏北导致模式预报降水落区偏北。可见,模式对西南低涡强降水有一定预报能力,因此,提高GRAPES-REPS中尺度集合预报能力,将有助于改进西南低涡强降水预报。

英文摘要：

The data of Global/Regional Assimilation and Prediction System-Regional Ensemble Prediction System （GRAPES-REPS） from June to August 2015 are used and an objective method based on grid data is designed for locating the center position of the southwest vortex. Firstly, the accuracy of GRAPES to the southwest vortex is tested, then 4 long-life southwest vortexes are picked to evaluate the ensemble forecas- ting performance of GRAPES-REPS in the generating, developing, moving and precipitation process of southwest vortex. The results show that. （1） accuracy of GRAPES to the southwest vortex keeps a high score, and the false rate is slightly larger than the missing rate. （2） GRAPES-REPS performs well in fore- casting generation and development of the southwest vortex. Most ensemble members can predict these processes, but the occurring time is earlier than observation. （3） The forecasted moving path for south- west vortex by GRAPES-REPS in 24 h is reasonable, the ensemble forecast is averagely much better than control member, and the path goes to north after 24 h in the eastward moving cases. （4） The forecast of the intensity of the southwest vortex is too strong, with higher value of center positive vorticity and lower value of geopotential height. （5） In 24 h forecast, the rain score for light rain to heavy rain triggered by the southwest vortex performs well, and the rainfall area matches the observation very well, while area for torrential rain lies slightly north in some cases, but mostly is reasonable. After 24 h, since the pathway of the eastward moving southwest vortexes is by north, the prediction of strong rainfall area follows the same trend. It can be seen that the system has the ability to forecast precipitation caused by the southwest vor-tex. So, improving the capability of mesoscale ensemble forecast by GRAPES-REPS would be helpful for the prediction of precipitation caused by the southwest vortex.