广州高建筑物雷电观测与研究10年进展

Advances of Observation and Study on Tall-object Lightning in Guangzhou over the Last Decade

作为中国气象局雷电野外科学试验基地(CMA_FEBLS)的重要组成部分,广州高建筑物雷电观测站(TOLOG)始建于2009年,迄今已积累数百次高建筑物雷电资料.对于雷电连接过程,高建筑物会起到"放大镜"的作用:TOLOG的观测在国际上首次发现了连接过程中负-正先导之间"头部-侧面"连接的现象,给出了先导连接行为的两种基本形态;揭示了负先导梯级发展过程的精细化结构,给出了下行先导和上行先导的二维/三维发展特征;估算了不同高度建筑物上雷电的闪击距离.高建筑物对雷电电磁场具有"放大器"的作用,且建筑物越高增强效应越显著.高建筑物是下行和上行闪电的"汇集点":对下行闪电的吸引作用可保护高建筑物附近的其他物体免遭雷击;正地闪的回击、延续电流和云内放电过程均可在高建筑物上触发负极性上行闪电.另外,高建筑物区域可作为闪电监测系统的"标校场",TOLOG的观测资料在地闪定位系统探测效率和定位精度的评估方面也得到了应用.

Comparing to the ground or low-object,tall-object is more likely to reach the threshold for the initiation of leader on its top due to the distortion and enhancement of electric field,therefore tall-object is not only easier to get struck by downward lightning,but also can initiate upward lightning.A field experiment,mainly focusing on the observation of lightning flashes terminating on tall structures,has been conducted since 2009 at the Tall-Object Lightning Observatory in Guangzhou(TOLOG),which is the important part of the Field Experiment Base on Lightning Sciences,China Meteorological Administration(CMA_FEBLS).Hundreds of tall-object lightning flashes have been captured during 2009-2018.For the lightning attachment process,tall-object will play the role of"magnifier":The TOLOG high-speed optical observation discovers the connection of the downward negative leader to the lateral surface of the upward connecting leader for the first time,and shows two basic types of the leader connection behaviors during the attachment process in negative cloud-to-ground lightning;the fine structure of negative stepped leader in natural lightning at close distance is revealed by using high-speed video records;the 2D/3D propagation characteristics of downward and upward leaders are analyzed;and the striking distances of lightning flashes to tall-object with different heights are also estimated.Tall-object plays an"amplifier"role on lightning electromagnetic field:Statistical analysis of the TOLOG data show that the magnetic field peak values induced by the first return stroke of lightning flashes to objects higher than 200 m is 2.4 times of that of lightning flashes to objects lower than 200 m;the higher the tall-object is,the larger the lightning location system inferred peak current of strokes are recorded in the vicinity of the tall-object;and the numberical simulation of the tall-object on electromagnetic field of lightning return stroke also show that the height of tall-object has significant enhancing effects.Tall-object is the"hot spot"of downward and upward lightning:Attraction effects of tall-object on downward lightning can protect other objects near tall-object from lightning strikes;the upward negative lightning from the tall-object can be triggered by the return stroke,the continuing current or the discharging process in cloud of positive cloud-to-ground lightning;and in upward lightning,abrupt extension is found at the positive end of the recoil leader which propagates bidirectionally.Using data of the TOLOG,the detection efficiency,the location error and the systematic bias of lightning location systems in Guangdong are evaluated,showing that the observation area of the TOLOG can be used as a"calibration field"for ground-based or space-based lightning monitoring system.