基于分段层次聚类的中国强降水集合平均预报逐步订正方法研究

A stepwise correction method based on segmented hierarchical clustering for ensemble mean forecasts of severe rainfall in China

  • 摘要: 集合预报在数值天气预报中占有重要地位,如何有效地从集合成员中提取信息以提高降水的集合平均预报技巧是重要科学问题。采用2019—2022年夏季中国气象局全球集合预报业务模式(China Meteorological Administration Global Ensemble Prediction System,CMA-GEPS)的逐日累计降水量集合预报数据,发展了基于分段层次聚类的逐步订正方法(Stepwise correction method based on segmented Hierarchical Clustering, SHC)以改进该模式的强降水集合平均预报结果,并定量评估了SHC方法的性能,比较了其与集合平均(EM)和直接聚类法(HC)的订正效果差异。结果表明:SHC方法由于采取了分段聚类订正来有效引入更有价值的集合成员预报信息,进而修正集合平均预报结果,提升目前在短、中期天气集合预报中的强降水预报能力;该方法的逐日连续预报检验评分总体在降水预报订正方面有优势,相对于EM和HC方法预报技巧均有明显提升,证明其具有良好的适用性;对于2021年郑州7·20暴雨个例的应用显示SHC方法对极端降水预报具有较好的订正效果。SHC方法为改进中国强降水集合平均预报技巧提供了新方法。

     

    Abstract: Ensemble prediction play a vital role in numerical weather prediction. Hence, how to effectively extract information from ensemble members to improve deterministic precipitation forecasting skills has always been a challenging issue. Based on precipitation data from the CMA-GEPS (China Meteorological Administration Global Ensemble Prediction System), a stepwise correction method based on Segmented Hierarchical Clustering (SHC) for daily precipitation is proposed. To evaluate the effect of the SHC method, two comparative experiments are further verified in this study based on TS score and ETS score. Effects of SHC are compared with that of an Ensemble Mean (EM) forecast method and a directed Hierarchical Clustering (HC) method. Results indicate that the deterministic forecast by the proposed SHC method can improve the predictability of heavy precipitation. Taking more probabilistic forecasting via the segmented correction scheme in correction method, SHC performs better than EM and HC. Meanwhile, SHC shows a better feasibility based on long-term forecast verification during the summertime in 2021; it also has much better effects on extreme precipitation event such as the case of heavy rainfall in Zhengzhou on 20 July 2021. For operational system, the developed SHC method provides a new tool that can further improve the result of ensemble forecasting.

     

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