弱天气尺度背景下太行山极端短时强降水预报失败案例剖析
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摘要
2015年7月31日夜间,太行山区出现极端短时强降水天气,石家庄和邢台的西部山区有5个雨量站雨量超过100mm,其中石家庄市赞皇县院头镇和邢台市临城县南中皋村最大雨强都超过50mm·h~(-1),3h雨量超过100mm,属极端短时强降水。数值预报、上级指导预报以及各级台站预报对暴雨均为漏报。本文利用常规高空地面观测资料、加密自动站观测资料、石家庄新一代天气雷达资料以及数值预报检验,反思该极端短时强降水预报思路和预报失败原因。此次极端短时强降水是发生在青藏高压东北侧高空西北气流的弱天气尺度背景下,预报的关键在于把握太行山东侧边界层偏东风与地形的作用、青藏高压加强使中层西北气流加强使垂直风切变加大、低层切变线东移影响、西南暖湿气流增强使水汽输送增加、中空干层与加厚的低空湿层叠加使对流不稳定性加强的特征。预报失误的主要原因是没有分析最大不稳定能量(订正CAPE值)导致对山西不稳定条件的低估,致使对山西雷暴在夜间的再次发展估计不足,同时预报员没能有效地使用非常规资料用于实时检验和订正数值预报结果,导致没能预见到雷暴下山增强的可能。目前对弱天气背景下强降水产生条件缺乏有效的概念模型,数值模式可预报性较差,未来需要提高预报员对观测资料的全面分析能力和对数值预报产品的释用能力,通过大量个例的研究发展有效的预报(概念)模型。
In midnight on 31 July 2015,an extreme flash-rain event was happened in Taihang Mountain.The rainfall was more than 100 mm at 5 automatic weather stations(AWSs)in mountain areas of Shijiazhuang and Xingtai,of which Yuantou town of Shijiazhuang City and Nanzhonggao Town of Xingtai City were caught by extreme short-time intense rainfall with rainfall amount more than 50 mm·h~(-1) and more than 100 mm·(3 h)~(-1).However,the numerical prediction,the superior guidance forecast and meteorological observatory all failed to forecast this rainstorm.Based on conventional upper-level and surface observations,AWS data,Doppler weather radar data and numerical forecast test,this paper analyzed the prediction ideas and the reason of failure.The event occurred under weak synoptic-scale background in northeast of Tibetan high.The key of forecasting severe precipitation was to grasp the effects of east wind in Taihang Mountain and terrain.The middle-level northwest flow strengthened vertical wind shear,lowlevel shear line moved eastward,southwest wind strengthened warm moist air flows,and dry air layer overlaid on the thicken wet layer,strengthening the convective instability.The primary reason of the forecast error is that the lack of analyzing the maximum CAPE led to underestimating the unstable conditions and the development of thunderstorm at night in Shanxi Province.In addition,forecasters failed to use the unconventional data for real-time testing and correct numerical results,thus failing to predict the enhancement of thunderstorm enhance when it went down the hill.There is no effective conceptual model for severe precipitation conditions in the weak weather background at present.Forecast capacity of numerical model for such weather is poor.So forecasters need to improve the comprehensive analysis ability on observational data and the interpretation capacity of numerical prediction products in the future,and also to develop effective forecasting conceptual model through studying a large number of cases.
In midnight on 31 July 2015,an extreme flash-rain event was happened in Taihang Mountain.The rainfall was more than 100 mm at 5 automatic weather stations(AWSs)in mountain areas of Shijiazhuang and Xingtai,of which Yuantou town of Shijiazhuang City and Nanzhonggao Town of Xingtai City were caught by extreme short-time intense rainfall with rainfall amount more than 50 mm·h~(-1) and more than 100 mm·(3 h)~(-1).However,the numerical prediction,the superior guidance forecast and meteorological observatory all failed to forecast this rainstorm.Based on conventional upper-level and surface observations,AWS data,Doppler weather radar data and numerical forecast test,this paper analyzed the prediction ideas and the reason of failure.The event occurred under weak synoptic-scale background in northeast of Tibetan high.The key of forecasting severe precipitation was to grasp the effects of east wind in Taihang Mountain and terrain.The middle-level northwest flow strengthened vertical wind shear,lowlevel shear line moved eastward,southwest wind strengthened warm moist air flows,and dry air layer overlaid on the thicken wet layer,strengthening the convective instability.The primary reason of the forecast error is that the lack of analyzing the maximum CAPE led to underestimating the unstable conditions and the development of thunderstorm at night in Shanxi Province.In addition,forecasters failed to use the unconventional data for real-time testing and correct numerical results,thus failing to predict the enhancement of thunderstorm enhance when it went down the hill.There is no effective conceptual model for severe precipitation conditions in the weak weather background at present.Forecast capacity of numerical model for such weather is poor.So forecasters need to improve the comprehensive analysis ability on observational data and the interpretation capacity of numerical prediction products in the future,and also to develop effective forecasting conceptual model through studying a large number of cases.
引文
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樊利强,王迎春,陈明轩,2009.利用雷达资料反演方法对北京地区一次强对流天气过程的分析[J].气象,35(11):9-16.
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王丛梅,俞小鼎,李芷霞,等,2017.太行山地形影响下的极端短时强降水分析[J].气象,43(4):425-433.
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王宇虹,徐国强,贾丽红,等,2015.太行山对北京“7.21”特大暴雨的影响及水汽敏感性分析的数值研究[J].气象,41(4):389-400.
吴庆梅,刘卓,王国荣,等,2015.一次华北暴雨过程中边界层东风活动及作用[J].应用气象学报,26(2):160-172.
肖现,陈明轩,高峰,等,2015.弱天气系统强迫下北京地区对流下山演变的热动力机制[J].大气科学,39(1):100-124.
俞小鼎,2012.2012年7月21日北京特大暴雨成因分析[J].气象,38(11):1313-1329.
俞小鼎,2013.短时强降水临近预报的思路与方法[J].暴雨灾害,32(3):202-209.
俞小鼎,周小刚,王秀明,2012.雷暴与强对流临近天气预报技术进展[J].气象学报,70(3):311-337.
Doswell Ⅲ C A,2001.Severe convective storms-an overview[J].Meteor Monogr,28(50):1-26.
Wilson J W,Feng Y R,Chen M,et al,2010.Nowcasting challenges during the Beijing Olympics:Successes,failures,and implications for future nowcasting systems[J].Wea Forecasting,25(6):1691-1714.
陈双,2011.弱天气尺度背景下的雷暴增强和新生的机理研究[D].北京:中国气象科学研究院.
樊利强,王迎春,陈明轩,2009.利用雷达资料反演方法对北京地区一次强对流天气过程的分析[J].气象,35(11):9-16.
郝莹,姚叶青,郑媛媛,等,2012.短时强降水的多尺度分析及临近预警[J].气象,38(8):903-912.
黄荣,2012.北京地区雷暴下山增强的特征分析及个例研究[D].北京:中国气象科学研究院.
雷蕾,孙继松,王华,等,2014.偏东风冷空气与地形相互作用背景下北京局地强降水成因分析[J].暴雨灾害,33(4):325-332.
孙继松,何娜,王国荣,等,2012.“7.21”北京大暴雨系统的结构演变特征及成因初探[J].暴雨灾害,31(3):218-225.
孙继松,雷蕾,于波,等,2015.近10年北京地区极端暴雨事件的基本特征[J].气象学报,73(4):609-623.
王丛梅,李国翠,田秀霞,等,2013.河北省南部强对流天气的时空分布及对流参数统计特征[J].气候变化研究快报,2(1):39-45.
王丛梅,俞小鼎,李芷霞,等,2017.太行山地形影响下的极端短时强降水分析[J].气象,43(4):425-433.
王丽荣,刘黎平,王立荣,等,2013.太行山东麓地面辐合线特征分析[J].气象,39(11):1445-1451.
王宇虹,徐国强,贾丽红,等,2015.太行山对北京“7.21”特大暴雨的影响及水汽敏感性分析的数值研究[J].气象,41(4):389-400.
吴庆梅,刘卓,王国荣,等,2015.一次华北暴雨过程中边界层东风活动及作用[J].应用气象学报,26(2):160-172.
肖现,陈明轩,高峰,等,2015.弱天气系统强迫下北京地区对流下山演变的热动力机制[J].大气科学,39(1):100-124.
俞小鼎,2012.2012年7月21日北京特大暴雨成因分析[J].气象,38(11):1313-1329.
俞小鼎,2013.短时强降水临近预报的思路与方法[J].暴雨灾害,32(3):202-209.
俞小鼎,周小刚,王秀明,2012.雷暴与强对流临近天气预报技术进展[J].气象学报,70(3):311-337.
Doswell Ⅲ C A,2001.Severe convective storms-an overview[J].Meteor Monogr,28(50):1-26.
Wilson J W,Feng Y R,Chen M,et al,2010.Nowcasting challenges during the Beijing Olympics:Successes,failures,and implications for future nowcasting systems[J].Wea Forecasting,25(6):1691-1714.