基于聚类分析的中国东部夏季降水集合预报频率匹配法订正研究

Study on frequency matching method of precipitation ensemble forecasts based on cluster analysis in eastern China

  • 摘要: 频率匹配法(Frequency Matching Method,FMM)和聚类分析都是降水预报常用的偏差订正方法,因此如何高效融合聚类分析和频率匹配法来提高降水集合预报技巧是重要的科学问题。为更有效地改善模式集合平均强降水漏报的问题,采用2020—2024年夏季欧洲中期天气预报中心全球集合预报系统的降水集合预报,设计了锚定频率的FMM方法,同时结合降水特征的聚类分析降水订正方法,构建了一套降水订正方法。订正方法的对比试验表明:聚类分析-集合采样-锚定频率的FMM (简称聚类FMM)能有效提升强降水(概率)预报能力,对100 mm降水量预报的分数技能评分比原始模式预报提升约30%—80%。华北“23·7”和湖南“24·7”极端降水个例检验结果显示,聚类FMM能有效修正模式预报的强降水干偏差。同时,聚类分析、集合采样方式及锚定频率的频率匹配实现方案均有利于集合预报得到更准确的强降水预报。本研究为改进强降水集合预报偏差订正提供了有效参考。

     

    Abstract: Both the Frequency Matching Method (FMM) and cluster analysis are widely recognized as standard bias correction techniques for precipitation forecasts. Therefore, how to effectively integrate cluster analysis with FMM to improve precipitation forecasting skills emerges as a critical scientific issue. To improve the forecasting skill of heavy rainfall, this study leverages forecasts from the European Centre for Medium-Range Weather Forecasts Global Ensemble Prediction System during the summers from 2020 to 2024. In this study, ablation experiments are designed based on the clustering results of historical precipitation characteristics and an FMM approach that anchors frequency. The Clustering-Ensemble sampling-anchoring frequency FMM (Cluster-FMM in short) significantly improves the (probability) forecasting skill of heavy rainfall events. Notably, the 100 mm Fractions Skill Score increases by 30%—80%. Two extreme precipitation cases ("23·7" in North China and "24·7" in Hunan Province) show that the Cluster-FMM results effectively correct the dry biases in ensemble forecasts of heavy precipitation. The ablation experiments also confirm that the clustering analysis, ensemble sampling and anchoring frequency collectively contribute to the enhancement of forecasting accuracy for heavy precipitation events. For operational systems, the Cluster-FMM provides a new perspective for improving accuracy of ensemble precipitation forecasts.

     

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