渤海西岸偏东风对天津局地大暴雨的影响分析
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摘要
利用加密自动气象站、多普勒天气雷达和风廓线雷达等高时空分辨率资料,分析2017年7月6日天津一次局地大暴雨过程的中尺度对流系统发展演变特征,讨论渤海西岸边界层偏东风的垂直结构、温湿特性及其对局地大暴雨的作用。结果表明:局地大暴雨由两个暖区中尺度对流系统和一个低涡切变线系统造成,偏东风作用下的暖区第二个中尺度对流系统主导了局地大暴雨的形成。大暴雨中心两侧的温湿特征均呈"东高西低"分布,偏东气流具有暖湿特性,为暖区对流暴雨的发生发展提供了有利的环境条件。由于海陆地形差异,偏东气流自渤海向内陆推进过程中呈现明显的风速扰动特征,不仅导致水汽辐合,同时有利于上升运动发展。其中,0.6 km以下偏东风的中尺度扰动对局地大暴雨的触发和维持起重要作用,风速辐合强迫产生的上升气流是γ中尺度对流单体的重要触发机制,而强降水冷池出流与不断增强的暖湿偏东人流相互作用形成地面中尺度辐合线,使对流系统得以稳定维持,40 dBz以上强降水回波持续近3 h,平均6 min降水量达6.8 mm。此外,局地大暴雨的雨强变化与东风急流波动关系密切,急流的建立、发展、减弱和消失分别对应降水的陡增、峰值、减弱和陡降四个阶段。
Based on the high spatio-temporal resolution data of automatic weather stations, Doppler weather radar and wind profiler radar, we analyzed the development of the mesoscale convective systems during the heavy rainfall in Tianjin on 6 July 2017, and discussed the structural characteristics of easterly flow from the Bohai Sea and its influence on the local heavy rainfall. The results are as follows: The local heavy rainfall was caused by two warm-zone mesoscale convective systems and a vortex shear line system. Among them, the second mesoscale convective system in warm area dominated the formation of local heavy rainfall, and it was closely related to the easterly flow in the boundary layer. The easterly flow during this heavy rainfall had warm and wet characteristics, which was conductive to the occurrence and development of heavy rainstorms. At the same time, the wind speed from the Bohai Sea to the inland showed obviously disturbance, leading to the convergence of water vapor in the boundary layer and the development of the ascending movement. Furthermore, the mesoscale disturbance of easterly flow below 0. 6 km played an important role in the triggering and maintaining mechanism of the heavy rainfall. Under the convergence system caused by the wind speed disturbance, the updraft flow was forced, triggering the occurrence of the meso-y-scale convection. On the other hand, the outflow of cold pool caused by the heavy rainfall and the increasing easterly inflow interacted each other and formed the convergence, and the meso-scale convective system was maintained stably, resulting in the strong precipitation echo above 40 dBz lasting nearly 3 h,with an average precipitation of 6. 8 mm per 6 min. In addition, the change of rain intensity was closely related to the fluctuation of the easterly jet in the boundary layer. The establishment, development, weakening and disappearance of the jet corresponded to the four phases of steep increasing, peak, weakening and steep dropping of precipitation.
Based on the high spatio-temporal resolution data of automatic weather stations, Doppler weather radar and wind profiler radar, we analyzed the development of the mesoscale convective systems during the heavy rainfall in Tianjin on 6 July 2017, and discussed the structural characteristics of easterly flow from the Bohai Sea and its influence on the local heavy rainfall. The results are as follows: The local heavy rainfall was caused by two warm-zone mesoscale convective systems and a vortex shear line system. Among them, the second mesoscale convective system in warm area dominated the formation of local heavy rainfall, and it was closely related to the easterly flow in the boundary layer. The easterly flow during this heavy rainfall had warm and wet characteristics, which was conductive to the occurrence and development of heavy rainstorms. At the same time, the wind speed from the Bohai Sea to the inland showed obviously disturbance, leading to the convergence of water vapor in the boundary layer and the development of the ascending movement. Furthermore, the mesoscale disturbance of easterly flow below 0. 6 km played an important role in the triggering and maintaining mechanism of the heavy rainfall. Under the convergence system caused by the wind speed disturbance, the updraft flow was forced, triggering the occurrence of the meso-y-scale convection. On the other hand, the outflow of cold pool caused by the heavy rainfall and the increasing easterly inflow interacted each other and formed the convergence, and the meso-scale convective system was maintained stably, resulting in the strong precipitation echo above 40 dBz lasting nearly 3 h,with an average precipitation of 6. 8 mm per 6 min. In addition, the change of rain intensity was closely related to the fluctuation of the easterly jet in the boundary layer. The establishment, development, weakening and disappearance of the jet corresponded to the four phases of steep increasing, peak, weakening and steep dropping of precipitation.
引文
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王丛梅,俞小鼎,刘瑾,等,2018.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[J].气象,44(1):107-117. Wang C M,Yu X D,Liu J,et al,2018. Analysis of a forecast failure case of extreme flash-rain under weak synoptic-scale background in Taihang Mountain[J]. Meteor Mon,44(1):107-117(in Chinese).
王坚红,杨艺亚,苗春生,等,2017.华南沿海暖区辐合线暴雨地形动力机制数值模拟研究[J].大气科学,41(4):784-796. Wang J H,Yang Y Y,Miao C S,et al,2017. The numerical study of terrain dynamic influence on warm area heavy rainfall of convergence lines in South China Coast[J]. Chinese J Atmos Sci,41(4):784-796(in Chinese).
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. Wu Q M,Liu Z,Wang G R, et al, 2015. The influence of boundary layer east wind on a North China rainstorm[J]. J Appl Meteor Sci,26(2):160-172(in Chinese).
徐明,赵玉春,高琦,等,2015.偏东气流诱发川西高原东侧两次对流暴雨过程的对比分析[J].气象,41(12):1477-1487. Xu M,Zhao Y C,Gao Q, et al,2015. Comparative analysis of easterly air stream triggering two convection rainstorms in the eastern side of Sichuan Plateau[J]. Meteor Mon, 41(12):1477-1487(in Chinese).
徐双柱,王丽,叶成志,等,2006.东风低空急流暴雨的中尺度分析[J].气象,32(2):28-33. Xu S Z,Wang L,Ye C Z,et al,2006. A meso-analysis of a heavy rainfall in low-level southeaster jet[J].Meteor Mon,32(2):28-33(in Chinese).
杨舒楠,路屹雄,于超,2017.一次梅雨锋暴雨的中尺度对流系统及低层风场影响分析[J].气象,43(1):21-33. Yang S N,Lu Y X,Yu C,2017. Analysis on mesoscale convective system and impact of low-level wind in a Meiyu heavy rainfall event[J]. Meteor Mon,43(1):21-33(in Chinese).
易笑园,李泽椿,朱磊磊,等,2010.一次β-中尺度暴风雪的成因及动力热力结构[J].高原气象,29(1):175-186. Yi X Y,Li Z C,Zhu L L,et al,2010. A case study on dynamic and thermal structures and mechanism ofβ-mesoscale snowstorm[J]. Plateau Meteor,29(1):175-186(in Chinese).
喻谦花,郑士林,吴蓁,等,2016.局部大暴雨形成的机理与中尺度分析[J].气象,42(6):686-695. Yu Q H,Zheng S L,Wu Z,et al,2016. The forming mechanism and mesoscale analysis of local heavy rainfall[J]. Meteor Mon,42(6):686-695(in Chinese).
张文龙,崔晓鹏,王迎春,等,2013.对流层低层偏东风对北京局地暴雨的作用[J].大气科学,37(4):829-840. Zhang W L,Cui X P,Wang Y C,et al,2013. Roles of low-level easterly winds in the local torrential rains of Beijing[J]. Chinese J Atmos Sci,37(4):829-840(in Chinese).
赵强,王楠,李萍云,等,2017.两次陕北暴雨过程热力动力机制诊断[J].应用气象学报,28(3):340-356. Zhao Q,Wang N,Li P Y,et al,2017. Diagnosis of thermal and dynamic mechanisms of two rainstorm processes in Northern Shaanxi[J]. J Appl Meteor Sci,28(3):340-356(in Chinese).
Stuart N A, Grumm R H,2006. Using wind anomalies to forecast East Coast winter storms[J]. Wea Forecasting,21(6):952-968.
何群英,孙一昕,2017.天津地区一次回流降雪过程结构特征及发生机理分析[J].气象与环境学报,33(1):26-33.He Q Y,Sun Y X,2017.Analysis on the structure and mechanism of a returnflow snow fall event in Tianjin[J].J Meteor Environ,33(1):26-33(in Chinese).
黄鹤,于雷,王志超,等,2013.一次回流降雪过程边界层东风结构分析[J].干旱气象,31(4):756-762.Huang H,Yu L,Wang Z C,et al.2013.Analysis of boundary layer easterly wind structure during a returning flow snowing weather process[J].J Arid Meteor,31(4):756-762(in Chinese).
孔凡超,赵庆梅,李江波,2016.2013年7月冀中特大暴雨的中尺度系统特征和环境条件分析[J].气象,42(5):578-588.Kong F C,Zhao Q M,Li J B,2016.Diagnostic analysis of mesoscale system and environmental conditions during Hebei severe rainstorm[J].Meteor Mon,42(5):578-588(in Chinese).
雷蕾,孙继松,何娜,等,2017.“7·20”华北特大暴雨过程中低涡发展演变机制研究[J].气象学报,75(5):685-699.Lei L,Sun J S,He N,et al,2017.A study on the mechanism for the vortex system evolution and development during the torrential rain event inNorth China on 20 July 2016[J]. Acta Meteor Sinica, 75(5):685-699(in Chinese).
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. Lei L,Sun J S,Wang H, et al,2014. Cause analysis of a local severe precipitation event in Beijing on the background of interaction of easterly cold air and topography[J]. Torrential Rain Disasters,33(4):325-332(in Chinese).
祁海霞,辜旭赞,白永清,等,2017. 2013年湖北一次大暴雨归中尺度分析和模拟诊断[J].气象,43(3):268-277. Qi H X,Gu X Z,Bai Y Q,et al,2017. Simulation and diagnosis of the evolution characteristics of a meso-βscale heavy rainstorm event in Hubei in2013[J]. Meteor Mon,43(3):268-277(in Chinese).
苏爱芳,张宁,黄勇,2016.“8·13”黄淮北部暴雨云团的组织结构和触发机制[J].气象,42(8):905-919,Su A F,Zhang N,Huang Y,2016. Organizational structure and trigger mechanism of rainstorm cloud clusters over North Huanghuai Region on 13 August 2010[J]. Meteor Mon,42(8):905-919(in Chinese).
孙继松,王华,王令,等,2006.城市边界层过程在北京2004年7月10日局地暴雨过程中的作用[J].大气科学,30(2):221-234.Sun J S,Wang H,Wang L,et al,2006. The role of urban boundary layer in local convective rain happening in Beijing on 10 July 2004[J]. Chinese J Atmos Sci,30(2):221-234(in Chinese).
孙继松,杨波,2008.地形与城市环流共同作用下的β中尺度暴雨[J].大气科学,32(6):1352-1364. Sun J S,Yang B,2008. Meso-βscale torrential rain affected by topography and the urban circulation[J]. Chinese J Atmos Sci,32(6):1352-1364(in Chinese).
孙建华,李娟,沈新勇,等,2015.2013年7月四川盆地一次特大暴雨的中尺度系统演变特征[J].气象,41(5):533-543. Sun J H,Li J,Shen X Y,et al,2015. Mesoscale system study of extreme rainfall over Sichuan Basin in July 2013[J]. Meteor Mon, 41(5):533-543(in Chinese).
孙密娜,易笑园,闫志超,等,2013.渤海西岸降雪过程中偏东风在250 m塔层内的特征分析[J].气象与环境学报,29(5):35-42.Sun M,Yi X Y,Yan Z C,et al,2013. Analysis of easterly wind during snow within the 250 m tower layer in western coast of the Bohai Sea[J]. J Meteor Environ,29(5):35-42(in Chinese).
田付友,郑永光,张小玲,等,2018.2017年5月7日广州极端强降水对流系统结构、触发和维持机制[J].气象,44(4):469-484. Tian F Y, Zheng Y G, Zhang X L, et al,2018. Structure, triggering and maintenance of convective systems during the Guangzhou extreme rainfall on 7 May 2017[J]. Meteor Mon,44(4):469-484(in Chinese).
王丛梅,俞小鼎,刘瑾,等,2018.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[J].气象,44(1):107-117. Wang C M,Yu X D,Liu J,et al,2018. Analysis of a forecast failure case of extreme flash-rain under weak synoptic-scale background in Taihang Mountain[J]. Meteor Mon,44(1):107-117(in Chinese).
王坚红,杨艺亚,苗春生,等,2017.华南沿海暖区辐合线暴雨地形动力机制数值模拟研究[J].大气科学,41(4):784-796. Wang J H,Yang Y Y,Miao C S,et al,2017. The numerical study of terrain dynamic influence on warm area heavy rainfall of convergence lines in South China Coast[J]. Chinese J Atmos Sci,41(4):784-796(in Chinese).
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. Wu Q M,Liu Z,Wang G R, et al, 2015. The influence of boundary layer east wind on a North China rainstorm[J]. J Appl Meteor Sci,26(2):160-172(in Chinese).
徐明,赵玉春,高琦,等,2015.偏东气流诱发川西高原东侧两次对流暴雨过程的对比分析[J].气象,41(12):1477-1487. Xu M,Zhao Y C,Gao Q, et al,2015. Comparative analysis of easterly air stream triggering two convection rainstorms in the eastern side of Sichuan Plateau[J]. Meteor Mon, 41(12):1477-1487(in Chinese).
徐双柱,王丽,叶成志,等,2006.东风低空急流暴雨的中尺度分析[J].气象,32(2):28-33. Xu S Z,Wang L,Ye C Z,et al,2006. A meso-analysis of a heavy rainfall in low-level southeaster jet[J].Meteor Mon,32(2):28-33(in Chinese).
杨舒楠,路屹雄,于超,2017.一次梅雨锋暴雨的中尺度对流系统及低层风场影响分析[J].气象,43(1):21-33. Yang S N,Lu Y X,Yu C,2017. Analysis on mesoscale convective system and impact of low-level wind in a Meiyu heavy rainfall event[J]. Meteor Mon,43(1):21-33(in Chinese).
易笑园,李泽椿,朱磊磊,等,2010.一次β-中尺度暴风雪的成因及动力热力结构[J].高原气象,29(1):175-186. Yi X Y,Li Z C,Zhu L L,et al,2010. A case study on dynamic and thermal structures and mechanism ofβ-mesoscale snowstorm[J]. Plateau Meteor,29(1):175-186(in Chinese).
喻谦花,郑士林,吴蓁,等,2016.局部大暴雨形成的机理与中尺度分析[J].气象,42(6):686-695. Yu Q H,Zheng S L,Wu Z,et al,2016. The forming mechanism and mesoscale analysis of local heavy rainfall[J]. Meteor Mon,42(6):686-695(in Chinese).
张文龙,崔晓鹏,王迎春,等,2013.对流层低层偏东风对北京局地暴雨的作用[J].大气科学,37(4):829-840. Zhang W L,Cui X P,Wang Y C,et al,2013. Roles of low-level easterly winds in the local torrential rains of Beijing[J]. Chinese J Atmos Sci,37(4):829-840(in Chinese).
赵强,王楠,李萍云,等,2017.两次陕北暴雨过程热力动力机制诊断[J].应用气象学报,28(3):340-356. Zhao Q,Wang N,Li P Y,et al,2017. Diagnosis of thermal and dynamic mechanisms of two rainstorm processes in Northern Shaanxi[J]. J Appl Meteor Sci,28(3):340-356(in Chinese).
Stuart N A, Grumm R H,2006. Using wind anomalies to forecast East Coast winter storms[J]. Wea Forecasting,21(6):952-968.