基于对流可分辨集合预报的阜宁龙卷概率预报研究

本文针对2016年6月23日江苏阜宁龙卷,设计了两组对流可分辨尺度集合预报:一组以ERA5再分析资料为初始和侧边界(CEFS_ERA5);另一组以NCEP GEFS为初始和侧边界(CEFS_GEFS),评估了两组试验对此次龙卷的预报能力。结果显示:两组对流尺度集合预报均有约半数以上成员能够再现龙卷超级单体的特征;2~5 km上升螺旋度(UH25)对本次龙卷超级单体有较好的预报指示意义。在上述分析的基础上,考虑位置预报偏差,提出了一种基于UH25的邻域龙卷概率预报产品,分析了龙卷概率预报技巧对关键参数邻域半径和UH25阈值的敏感性,CEFS_ERA5邻域半径取15个格点,UH25阈值取250 m²·s^-2最优;而CEFS_GEFS邻域半径取15个格点,UH25阈值取100 m²·s^-2最优。总的来说,邻域概率预报产品显著提升了对此次龙卷概率预报水平。

Probabilistic forecasting of Funing significant tornado based on convection-allowing ensembles

For the significanttornado that occurred in Funing, Jiangsu Province on June 23, 2016, two Convection-allowing Ensemble Forecast Systems (CEFSs) were designed: one initialized from ERA5 reanalysis dataset (named CEFS_ERA5) and the other initialized from NCEP GEFS (named CEFS_GEFS). The predictability of these two systems was evaluated and the results show that more than half of the members of the two ensemble systems can reproduce the typical characteristics of the tornadic supercell; 2-5 km updraft helicity (UH25)has good skill in indicating tornadic supercell. Further,considering the position prediction deviation, a neighborhood tornado probabilistic forecasting product based on UH25 is proposed. The sensitivity of probabilistic forecastingto the key parameters of the product, such as neighborhood radius and UH25 threshold, is analyzed: CEFS_ ERA5 taking 15 grid spacing as the neighborhood radius and 250 m² ·s^-2 as the UH25 threshold has the best skill; CEFS_ GEFs taking 15 grid spacing as the neighborhood radius and 100 m²·s^-2 as the UH25 threshold has the best skill. In general, the neighborhood probabilistic forecasting products based on UH25 have significantly improved the skill in predicting this tornado.