一次夏季冷锋后暴雨的形成机制探析
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摘要
利用常规观测资料,卫星、雷达及NCEP再分析资料,对2013年7月9日山西太原至河北石家庄一带的暴雨成因分析表明:(1)山西太原附近的暴雨发生在持续性层云弱降水持续6 h之后,层云中镶嵌积云并伴有弱雷电活动,暴雨区位于地面冷锋北侧低层冷区中,距离地面锋面120 km以上,极易漏报;(2)850 hPa东北风显著增强,低层假相当位温小的干冷空气随东北风向西南方向伸展,低层稳定层持续增厚,不稳定区位于稳定的边界层之上,强降水由高架对流造成;低层东北风和高层西南风同时增强,锋区斜压性显著增强,锋面抬升加强,锋面抬升和与500 hPa西南气流相伴的干平流使得锋区上空大气层结由近中性的绝对稳定转化为位势不稳定,锋区抬升使得位势不稳定转化为条件性不稳定;(3)午后河北中西部大气层结绝对稳定,石家庄雷达监测到其附近数条平行于热成风方向的水平尺度几十千米的对流云带是由条件性对称不稳定导致的倾斜对流。
By using conventional meteorological data, satellite data, radar data and NCEP reanalysis data,the instability formation process of a torrential rainfall from Taiyuan to Shijiazhuang on 9 July 2013 is studied. The results show that the torrential rainfall near Taiyuan occurred after light stratiform precipitation existed for six hours. The convective precipitation with weak thunder and lightning was embedded in the stratiform and it was located behind the cold front, more than 120 km away from surface front. Such cold sector torrential rainfall is easy to be missed. From 08:00 BT to 14:00 BT, depth of planetary boundary layer(PBL) cold air was continuously deepening, the dry and cold air mass with low pseudo-equivalent potential temperature extended from northeast to southwest, and the unstable atmosphere was situated over the stable boundary layer, so the torrential rain was caused by elevated convection. The northeast wind at850 hPa and the southwest wind at 500 hPa were strengthened at the same time, baroclinicity of frontal zone got stronger, the atmospheric stratification was transformed from absolute stability, which was almost neutral, to potential instability by the dry advection in 400 ——500 hPa and was moistened at lower level by frontal lifting. The potential unstable layer changed to conditional unstable layer by the frontal lifting of warm and humid air layer. In the afternoon, the atmosphere was absolutely stable near Shijiazhuang.The convective lines parallel to the thermal wind were observed near Shijiazhuang Radar Station. The mesoscale parallel convective lines were forced by conditional symmetric instability.
By using conventional meteorological data, satellite data, radar data and NCEP reanalysis data,the instability formation process of a torrential rainfall from Taiyuan to Shijiazhuang on 9 July 2013 is studied. The results show that the torrential rainfall near Taiyuan occurred after light stratiform precipitation existed for six hours. The convective precipitation with weak thunder and lightning was embedded in the stratiform and it was located behind the cold front, more than 120 km away from surface front. Such cold sector torrential rainfall is easy to be missed. From 08:00 BT to 14:00 BT, depth of planetary boundary layer(PBL) cold air was continuously deepening, the dry and cold air mass with low pseudo-equivalent potential temperature extended from northeast to southwest, and the unstable atmosphere was situated over the stable boundary layer, so the torrential rain was caused by elevated convection. The northeast wind at850 hPa and the southwest wind at 500 hPa were strengthened at the same time, baroclinicity of frontal zone got stronger, the atmospheric stratification was transformed from absolute stability, which was almost neutral, to potential instability by the dry advection in 400 ——500 hPa and was moistened at lower level by frontal lifting. The potential unstable layer changed to conditional unstable layer by the frontal lifting of warm and humid air layer. In the afternoon, the atmosphere was absolutely stable near Shijiazhuang.The convective lines parallel to the thermal wind were observed near Shijiazhuang Radar Station. The mesoscale parallel convective lines were forced by conditional symmetric instability.
引文
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孔凡超,李江波,张迎新,等,2015.华北冷季一次大范围雷暴与暴雪共存天气过程分析[J].气象,41(7):833-841. Kong F C,Li J B,Zhang Y X, et al,2015. Diagnostic analysis of one widespread thunderstorms coexisting with snowstorm in North China in March 2003[J]. Meteor Mon,41(7):833-841(in Chinese).
刘勇,徐娟娟,李明娟,等,2013.陕西中南部一次秋季连阴雨中区域性暴雨的成因分析[J].高原气象,32(3):739-749. Liu Y,Xu J J,Li M J, et al,2013. Analysis on regional torrential rainstorm during a consecutive autumn rain event in central and southern Shaanxi[J]. Plateau Meteor,32(3):739-749(in Chinese).
农孟松,赖珍权,梁俊聪,等,2013. 2012年早春广西高架雷暴冰雹天气过程分析[J].气象,39(7):874-882.Nong M S,Lai Z Q,Liang J C,et al,2013. Analysis on elevated thunderstorms hail in Guangxi in early spring of 2012[J]. Meteor Mon,39(7):874-882(in Chinese).
盛杰,毛冬艳,沈新勇,等,2014.我国春季冷锋后的高架雷暴特征分析[J].气象,40(9):1058-1065. Sheng J,Mao D Y,Shen X Y,et al.2014. Analysis on characteristics of elevated thunderstorms behind cold fronts in China during spring[J]. Meteor Mon,40(9):1058-1065(in Chinese).
王秀明,俞小鼎,周小刚,2014.雷暴潜势预报中几个基本问题的讨论[J].气象,40(4):389-399. Wang X M,Yu X D,Zhou X G,2014. Discussion on basical issues of thunderstorms potential forecasting[J]. Meteor Mon,40(4):389-399(in Chinese).
吴乃庚,林良勋,冯业荣,等,2013. 2012年初春华南“高架雷暴”天气过程成因分析[J].气象,39(4):410-417. Wu N G,Lin L X,Feng Y R,et al,2013. Analysis on the causes of an elevated thunderstorms in early-spring of South China[J]. Meteor Mon,39(4):410-417(in Chinese).
吴庆梅,杨波,王国荣,2014.北京地区一次回流暴雪过程的锋区特征分析[J].高原气象,33(2):539-547. Wu Q M,Yang B,Wang G R,2014. Analysis of the frontal characteristics of the backflow snowstorm process in Beijing area[J]. Plateau Meteor, 33(2):539-547(in Chinese).
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. Yu X D,Zhou X G,Wang X M,2012. The advances in the nowcasting techniques on thunderstorms and severe convection[J]. Acta Meteor Sinica,70(3):311-337(in Chinese).
俞小鼎,周小刚,王秀明,2016.中国冷季高架对流个例初步分析[J].气象学报,74(6):902-918. Yu X D,Zhou X G,Wang X M,2016. Preliminary case study of elevated convection in China[J].Acta Meteor Sinica, 74(6):902-918(in Chinese).
张一平,俞小鼎,孙景兰,等,2014. 2012年早春河南一次高架雷暴天气成因分析[J].气象,40(1):48-58. Zhang Y P,Yu X D,Sun J L,et al,2014. Analysis on weather causes of an elevated thunderstorm in Henan in early spring 2012[J]. Meteor Mon,40(1):48-58(in Chinese).
Colman B R,1990a. Thunderstorms above frontal surfaces in environments without positive CAPE. Part I:a climatology[J]. Mon Wea Rev,118(5):1103-1121.
Colman B R,1990b. Thunderstorms above frontal surfaces in environments without positive CAPE. PartⅡ:organization and Instability Mechanisms[J]. Mon Wea Rev,118(5):1123-1144.
Grant B N,1995. Elevated cold-sector severe thunderstorms:a preliminary study[J]. Natl Wra Dig, 19(4):25-31.
Markowski P,Richardson Y,2010. Mesoscale Meteorology in Midlatitudes[M]. Hoboken:John Wiley&Sons,Ltd.:407.
Moore J T,Glass F H,Graves C E,et al,2003. The environment of warm-season elevated thunderstorms associated with heavy rainfall over the central united states[J]. Wea Forecasting,18(5):861-878.
Morcrette G J,Browning K A,2006. Formation and release of symmetric instability following Delta-madjustment[J]. Quart J Roy Meteor Soc, 132(617):1073-1089.