基于多套卫星资料的ERA5全球小时降水频率评估

Evaluation of the global hourly precipitation frequency in ERA5 using multiple satellite datasets

最近发布的新一代全球再分析资料集ERA5,提供了全球小时降水再分析值,为全球小时降水研究提供又一个数据参考。然而,目前针对ERA5小时降水频率的评估工作还较为有限。本研究采用多套全球卫星观测小时降水对ERA5小时降水的频率进行了评估。对比分析发现:尽管ERA5总降水量与卫星资料出现较好的一致性,但ERA5的小时降水频率约为卫星资料的2~3倍,呈现系统性偏高。进一步分析表明,这主要是由于ERA5大大高估了中、低强度降水事件的数量。其中,ERA5对弱降水频率的高估尤为明显,平均可达卫星降水频率的6倍;此外,ERA5对海洋降水频率的高估程度也大于陆地。ERA5小时降水频率的系统性高估问题对相关研究的潜在影响,尚在进一步评估中。

The newly released ERA5 reanalysis dataset by the ECMWF provides hourly precipitation reanalysis values,adding another reference for global hourly precipitation research.However,current evaluations of ERA5 hourly precipitation are limited,focusing more on monthly and daily precipitation assessments or hourly precipitation within restricted areas.Few studies address global-scale assessments of hourly precipitation.Motivated by this gap,we assess the global hourly precipitation frequency of ERA5.Sparse station-observed hourly precipitation data,particularly over open oceanic and remote inland areas,limits its usefulness for global-scale assessment of ERA5 reanalysis precipitation data,despite its presumed accuracy over satellite estimates or precipitation reanalysis data.Consequently,we employ four satellite datasets—GPM,GSMaP-M,GSMaP-G,and CMORPH—to evaluate hourly precipitation frequency of ERA5 in this study.We analyze the spatial distribution of climatological annual total precipitation and precipitation frequency in ERA5 and the four satellite datasets.Additionally,we examine the error sources of hourly precipitation frequency of ERA5 by evenly dividing precipitation events from the 5 datasets into ten intensity bins based on the hourly precipitation intensity percentiles.We then compare precipitation frequency differences among different regions,including tropical and extra-tropical areas,as well as marine and land areas.The main findings are as follows:1)the magnitude and spatial pattern of climatological annual total precipitation of ERA5 close align with the four satellite datasets,indicating ERA5 effectively represents total precipitation.2)The climatological hourly precipitation frequency of ERA5 is 2-3 times higher than that of satellite data,suggesting a systematic error in the hourly precipitation frequency of ERA5 compared to satellite estimates,or an overestimation of average precipitation frequency of ERA5.3)The overall overestimation of hourly precipitation frequency of ERA5 mainly stems from an abnormal overestimation of moderate and light precipitation frequencies.Notably,ERA5 s global average for the lightest hourly precipitation(0—10%)is approximately 6 times higher than that observed in satellite estimations.4)ERA5 underestimates the frequency of extreme hourly precipitation compared to satellite estimations.5)In addition,oceanic overestimation is generally greater than that on land,with slightly stronger overestimation in the tropical region compared to the extratropical region.Although ERA5 systematically overestimates hourly precipitation frequency,its spatial pattern remains close to satellite estimates.The potential impact of this systematic overestimation in ERA5 on related research warrants further evaluation.