降水检验方案变化对降水检验评估效果的影响分析

为了实现对中尺度模式降水预报产品的合理化统计检验,在我国现有观测系统条件下,研究了24小时加密降水观测实况对降水统计检验评分的影响。过去的标准检验系统观测站为400站,分为9个区,目前业务试运行的加密检验系统采用的观测站为2510站,分为33个区。同时对国外常用的统计检验量ETS评分进行了初步的研究。通过对2005年7—8月我国近年来引进或自主发展的T213L31、HLAFS25、MM5、MESO-GRAPES60km和30km模式,WRF20km模式,以及日本及德国的全球模式的降水预报产品的统计学检验,主要得到如下结论:(1)加密检验系统和标准检验系统在站点分布和分区形式上有较大的差别,新旧检验系统对各模式和预报员全国降水预报的评估结论在大雨以下各级降水评估方面差别不大,结论基本相似,除中雨预报外,加密系统的TS评分均略低于标准检验的结果。暴雨以上评分的差别较大,其中部分模式的两个检验系统的预报偏差差别很大,说明暴雨以上的天气系统多为中小尺度系统,其发生的频率在加密系统中的反映可能更合理一些。(2)新的检验量ETS,对于全国这样较大的检验分区而言,大雨以下各级降水评分在量值上要小于TS评分,暴雨以上则比较接近,但其在多模式对比检验中所得的排序结论与TS和技巧评分相近,部分小雨空报较多的模式的评分有较大差别。(3)无论是加密检验,还是标准检验,各级降水检验中表现最好的模式是相同的。(4)分区相同、预报种类不同时,加密检验与标准检验的差别不同。对T213模式而言,两者在暴雨和大暴雨的预报偏差上的差别更显著一些,部分分区检验结论相反。而对预报员的预报而言,差别并不显著,检验结论一致。

Effect of Different Verification Schemes on Precipitation Veri fication and Assessment Conclusion

Multitudinous precipitation predictions are verified and assessed during July and August 2005.These products include the forecast of forecasters in Central Meteorological Office and NWP models,such as T213l31,HLAFS25,MM5,MESO-GRAPES 60km and 30km model,WRF20km,as well as Japanese and German global model outputs.Different kinds of rainfall verification schemes and statistical verification variables are used.The results show that the verification conclusions of different verification schemes on 8 kinds of NWP models and forecaster's rainfall prediction from light rain to heavy rain are near each other,whereas there are obvious differences on observation stations distribution between dense verification and standard verification.TS of dense verification system is lower than that of standard verification system.But for torrential rain and severe rain,bias of two verification systems are obviously different.The reason is that most of the weather systems resulting in torrential rain are meso-scale or micro-scale weather systems,their frequency is similar with dense verification observation.For whole country,ETS is less than TS for the rainfall under heavy rain,and is near for the rainfall over torrential rain.However,the sort of verification results on ETS for kinds of models is similar with TS or SS score except for light rain.Not only for dense verification,but also for standard verification,the best product of all verified forecasts is the same for all classes.If the area is the same,but the forecasts are different,the differences between dense verification and standard verification are different.For T213L31 model,the dense verification biases of some areas for torrential rain are obviously different from standard verification,but for forecaster's prediction,the results of two verification systems are similar.