研究山西极端暴雨发生规律对开展预报预警、灾害防御具有重要意义.本文利用常规观测资料和欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析资料(ERA5),采用标准化距平作为异常度,运用环流分析和物理量诊断等方法,研究1981-2018年6-9月山西17次极端暴雨的气候特征、环流影响系统和水汽异常特征.结果表明:山西极端暴雨主要出现在7-8月,暴雨区主要位于中南部,2010年以来极端暴雨明显多发;影响系统主要是700 hPa低涡和台风系统,有偏南和偏东两支水汽通道.极端暴雨过程中,低层水汽含量明显偏高,从暴雨区平均比湿的过程最大值看,大部分过程850 hPa超过14.2 g·kg-1,700 hPa则可超过9.8 g·kg-1、对应暴雨区平均异常度达1.6 以上;水汽的极端性在低层水汽通量辐合中心表现突出,17次极端暴雨700、850 hPa暴雨区水汽通量辐合中心过程最大值的异常度均值分别达-8、-6,其中台风减弱低压影响下的极端暴雨850 hPa水汽通量辐合中心最大异常度达-12.根据以上环流和水汽特征建立极端暴雨概念模型,并给出极端暴雨低层水汽含量和水汽通量辐合强度预报参考指标.
Study on circulation characteristics and water vapor anomaly of extreme rainstorm events in Shanxi Province
Study on the regularity of extreme rainstorm in Shanxi Province is of great significance for carrying out forecast and warning and disaster prevention.Based on the conventional observation data and the fifth generation atmospheric reanalysis(ERA5)from Euro-pean Centre for Medium-Range Weather Forecasts(ECMWF),the climatic characteristics,circulation impact systems,and water vapor anomaly characteristics were studied about 17 extreme rainstorm events in Shanxi Province from June to September during 1981-2018 by using circulation analysis and physical quantity diagnostics methods,along with using standardized anomaly as abnormal degree.The results show that extreme rainstorms in Shanxi Province mainly occurred in July and August,the rainstorm areas were mainly lo-cated in the central and southern parts,extreme rainstorms have occurred more frequently since 2010.The main impact systems were 700 hPa low vortex and typhoon system,and there were two water vapor channels from south and east.The moisture in the lower layers were significantly high during extreme rainstorms,for the maximum value of mean specific humidity on rainstorm area during extreme rainstorm process,most cases exceeded 14.2 g·kg-1 on 850 hPa,and exceeded 9.8 g·kg-1 on 700 hPa,which corresponding average ab-normal degree on rainstorm areas exceeded 1.6.The extreme of water vapor was prominent in the vapor flux convergence center in the lower layers,the mean abnormal degree for the maximum values of the vapor flux convergence center during the process over rainstorm areas on 700,850 hPa for 17 extreme rainstorms were-8,-6,respectively,wherein,the maximum abnormal degree of vapor flux con-vergence center on 850 hPa under the extreme rainstorm influenced by weakened typhoon low pressure could up to-12.Based on above circulation and water vapor characteristics,the conceptual models of extreme rainstorm are established,the forecasting reference indexes of moisture content and vapor flux convergence intensity on low layers are given.
extreme rainstormcirculation characteristicswater vapor anomalyforecasting index
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