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三种邻域概率方法在“23·7”华北特大暴雨预报中的对比分析

Comparisons of three neighborhood ensemble probability forecasting methods for the July 2023 severe torrential rain in North China

  • 摘要: 为探究邻域集合概率预报对改善强降水集合预报不确定性的实际效果,基于中国气象局区域集合预报系统(CMA-REPS),应用邻域集合概率预报(NEP)、集合平均邻域概率预报(EMNP)以及优化的邻域集合概率预报(ONEP)三种邻域集合概率预报方法(简称邻域概率方法,下同)和传统概率预报(TEP)方法,针对“23·7”华北特大暴雨过程开展强降水概率预报对比试验。通过系统评估三种方法在强降水概率预报空间分布特征、概率预报评分、不同概率阈值下的预报表现以及对邻域尺度的敏感性,综合比较各方法的优势与不足。结果表明:(1) 60 km邻域尺度,ONEP预报的强降水概率分布范围及形态与实况最为接近,EMNP与NEP的预报范围则相对偏小。随着邻域尺度增大,ONEP空报剧增但核心区降水概率维持稳定,EMNP与NEP的漏报率缓慢降低、但中心概率值显著降低,以EMNP尤为突出。(2) ONEP强降水预报效果对邻域尺度较为敏感,在60~140 km邻域尺度内统计评分最优;NEP评分随邻域尺度波动小,其预报优势主要体现在140 km以上邻域尺度;EMNP整体预报技巧不及ONEP和NEP。(3) EMNP、NEP与ONEP强降水预报最优公平技巧评分(Equitable Threat Score,ETS)均优于TEP,其中EMNP和NEP对应的潜势概率阈值仅为5 %~25 %,而ONEP潜势概率阈值可达60 %~80 %。(4) 邻域概率方法通过对空间邻域内集合信息的统计处理,有效降低了传统概率预报对模式位置误差的敏感性。研究结果为此类强降水事件的精细化预报提供了一种可参考的技术方案。

     

    Abstract: To investigate the effectiveness of neighborhood ensemble probability forecasting in reducing uncertainties of heavy precipitation ensemble forecasts, a comparative study was conducted for the July 2023 severe torrential rain in North China. Three neighborhood ensemble probability forecasting methods— Neighborhood Ensemble Probability (NEP), Ensemble Mean Neighborhood Probability (EMNP) and Optimized Neighborhood Ensemble Probability (ONEP)—were compared with the Traditional Ensemble Probability (TEP) approach using forecasts from the China Meteorological Administration Regional Ensemble Prediction System (CMA-REPS). These methods were systematically assessed in terms of spatial distribution characteristics, probabilistic forecast scores, forecast skill at different probability thresholds, and sensitivity of above metrics to neighborhood scales. The results show that: (1) At a neighborhood scale of 60 km, the spatial distribution and pattern of heavy rainfall probability in ONEP are closest to observations, while the forecast areas of EMNP and NEP are relatively smaller. As the neighborhood scale increases, the false alarms of ONEP sharply increases, but the probability values in the core rainfall area remain relatively stable. In contrast, the misses of EMNP and NEP gradually decrease, but their central probability values significantly decrease, especially for EMNP. (2) The performance of ONEP is sensitive to the neighborhood scale, achieving best Area under the Relative Operating Characteristic curve (AROC) and Brier Score at scales between 60 and 140 km. The AROC and Brier Score of NEP show less fluctuation with varying neighborhood scale, with its advantages primarily manifested at neighborhood scales larger than 140 km. Overall, EMNP exhibits lower forecast skill compared to ONEP and NEP. (3) The best Equitable Threat Score (ETS) of EMNP, NEP, and ONEP are better than that of TEP. The probability thresholds associated with the best ETS of EMNP and NEP are relatively low, ranging from only 5% to 25%, whereas the threshold of ONEP can reach 60% to 80%. (4) The study demonstrates that neighborhood probability methods effectively reduce the sensitivity of traditional probability forecasting to the model position errors through the statistical processing of the ensemble information within a spatial neighborhood, and provide a valuable technical approach for the refined forecasting of such extreme precipitation events. Nevertheless, additional case studies are required to assess the robustness and general applicability of these conclusions.

     

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