多种模式降水预报的稳定性特征研究

Stability Characteristics of Multi-Model Precipitation Forecast

预报的稳定性是指对同一时段在不同时间发布的多时效预报结论的一致性,是模式预报质量的一个重要方面,较大的不稳定性会给使用者造成困扰。为深入了解业务常用模式的稳定性,使用相对标准偏差指标计算不同时效预报的降水量波动大小,并改进了Flip-Flop指数(改进后简称FF_(norm)),计算多时效降水量预报变化趋势的翻转程度,衡量预报变化趋势的稳定性,对2种全球模式(ECMWF、NCEP-GFS)、3种区域模式(CMA-MESO、CMA-SH9、HHUPS-ST),在中国6个气候分区中降水预报的稳定性进行对比分析,分为实况有降水和暴雨及以上降水2种情况进行了讨论。结果表明:实况有降水时,相对区域模式来说,全球模式的多时效降水预报的相对标准偏差较小,即模式降水量预报的波动较小;各模式对西南区的西部、东北区的东部以及华南区的南部预报的波动性相对较小,西北区的西部波动性较大。就多时效降水量预报变化趋势而言,2种情况下均为CMA-MESO、NCEP-GFS和ECMWF的稳定性较好,其FF_(norm)指数小于HHUPS-ST和CMA-SH9模式,其中CMA-MESO对西南区、华南部分地区降水量预报变化趋势的稳定性较为突出;CMA-SH9的指数最大,多时效降水量预报变化趋势稳定性较差;各模式对长江中下游地区的FF norm指数相对较大,多时效预报趋势的稳定性较差。有降水时,CMA-MESO随时效临近的降水量预报变化趋势稳定(单调递增、单调递减或不变)的频次最多,其次是NCEP-GFS,2种降水情况下,该2种模式的降水量预报均为随时效临近单调递增次数大于递减次数,且CMA-MESO单调递增特征尤其显著。以上特征能够为模式调试和预报决策提供参考。

The stability of forecast refers to the consistency of multiple timeliness forecast conclusions issued at different times in the same period.It is an important aspect of the model system,and the large instability will cause trouble to users.In order to understand the stability of common operational models,the relative standard deviation index is used to calculate the magnitude of precipitation fluctuation,and the Flip-Flop index(FF_(norm))is improved to measure the reversal degree of precipitation forecast trend in this paper.Besides,the stability of precipitation forecast in two global models(ECMWF,NCEP-GFS)and three regional models(CMA-MESO,CMA-SH9,HHUPS-ST)in six climate zones in China,is discussed on the basis of the two cases of the observed precipitation and the rainstorm and the above.The results are as follows.When there is precipitation,the relative standard deviation of multiple timeliness precipitation forecasts of global models is smaller than that of regional models.That is,the fluctuation of model precipitation forecast is small.The volatility of each model for the western part of the southwest region,the eastern part of the northeast region and southern part of South China is smaller,while that for the western part of the northwest region is larger.In terms of the change trend of multiple timeliness precipitation forecast,the stability of CMA-MESO,NCEP-GFS and ECMWF is better in the two cases,and the index of FF_(norm) is smaller than that of HHUPS-ST and CMA-SH9.Among them CMA-MESO has a more prom-inent stability effect in the forecast for Southwest China and parts of South China.The index of CMA-SH9 is the largest and the model forecast is unstable.Each model has a relatively large index in the middle and lower reaches of the Yangtze River,and the stability of multiple timeliness forecast is poor.When there is precipitation,the frequency of stable(monotonically increasing or decreasing or constant)trend of precipitation forecast of CMA-MESO is the most,followed by NCEP-GFS.Under the two precipitation conditions,the precipitation forecast of the two models for each region is that the number of monotonically increasing times is greater than the number of decreasing times,and the monotonically increasing characteristics of the CMA-MESO model are particularly significant.The above characteristics could provide some references for model debugging and forecast decision-making.