闪电先导三维自持发展模式的建立

为研究上行先导发生发展的特征及其与地面构筑物间的相互作用,该文建立了闪电先导三维自持发展模式。该模式能够在给定雷暴云下空间电场初始分布情况、下行梯级先导始发位置及地面构筑物几何形状等参量时,进行自持发展模拟,计算出上行正先导随时间在三维空间内的头部位置、速度、电流强度、线电荷密度等物理特征量的变化。模拟发现上行正先导始发及发展过程中,其速度呈逐渐增加趋势,临近最后一跳发生前,上行正先导速度增加明显,整个过程中先导速度的变化范围为104~106 m·s-1量级,电流强度随时间也具有逐渐增加趋势,该变化趋势与光学观测得到的先导头部亮度的变化趋势相一致。该闪电先导三维自持模拟模型能够为进一步研究雷击地面构筑物特点提供参考。     

地闪三维随机模型的改进及多上行先导的数值模拟研究

为了探讨地闪连接过程中多上行先导的起始与发展,考虑到光学观测事实及雷暴电场环境,本研究在已有多上行先导三维随机参数化方案的基础上,植入背景电场模块并改进上、下行先导模块。基于新模型开展大量敏感性试验,结果如下:（1）新模型模拟的下行先导形态多样、分支数大幅度减少,能更好地再现多样的地闪连接过程。（2）在孤立建筑物情况下,上行先导长度、闪击距离以及触发多上行先导的次数与建筑物高度成正相关。（3）随着建筑物增高,同一次地闪中首个始发的上行先导与后续始发的上行先导间的起始时间差整体呈现上升趋势。初步研究表明:建筑物高度对触发多上行先导的影响显著。此外,受到建筑物高度及正、负先导发展情况的影响,低矮建筑物触发的多上行先导几乎同时起始,而高建筑物上允许首个始发的上行先导优先发展一定长度后再始发后续上行先导。      

空中人工引发雷电的正负先导特征研究

通过对 1998年 8月 2 2日空中引发雷电先导过程的光、电观测资料的综合分析发现 ,在空中引发雷电的先导系统中存在三个先导过程。①向下发展的负先导在起始阶段呈小阶梯特征 ,阶梯之间的时间间隔约为 2 0 μs ,阶梯的上升时间小于 1μs,随着负先导的下行发展 ,梯级增长。②金属导线上端向上发展的正先导在负先导接地之后 ,表现出明显的阶梯特性 ,阶梯之间的时间间隔平均为 15 μs。③从地面向上发展的连接正先导由多个振荡脉冲组成 ,脉冲之间的时间间隔约为 13μs,连接先导的发展也是梯级的。电场快变化中的高频分量随着距离的增加衰减很快。最强的发光是由向下的负先导接地时形成的小回击产生的 ,强光只集中在空气离化而形成的放电通道部分 ,光强则随着高度的增加很快衰减 ,其传播速度约为 2 .1× 10 8m·s-1。在小回击发生之前 ,向下发展的负先导在接地之前有较强的发光 ,而金属导线上端向上发展的正先导没有明显的发光。在小回击发生之后 ,金属导线上端向上正先导的发光强度被增强 ,其向上的传播速度约为 2 .4× 10 6m·s-1。金属导线部分在小回击发生之后约 2 2 0μs逐渐开始熔化发出强光 ,并向上发展而与前面向上发展的正先导的发光相并合 ,其传播速度约为 1× 10 6m·s-1     

Optical Observations on Propagation Characteristics of Leaders in Cloud-to-Ground Lightning Flashes

Using 2 high-speed cameras, we have recorded 14 negative cloud-to-ground (CG) lightning flashes, half of which are natural and the others are artificially triggered. The two-dimensional (2D) propagation speed of different type leaders and the luminosity of lightning channel are analyzed in detail. Bidirectional leader processes are observed during the initial processes of two altitude triggered negative lightning (ATNL)flashes. The analysis shows: the propagation speed of the upward positive leader (UPL) before the initiation of the downward negative leader (DNL) is at the order of 104-105 m s-1; the UPL can be intensified by the initiation and development of the DNL in the way that the luminosity is enhanced and the speed is sped up; after initiation, the DNL in one ATNL flash propagates downward three times intermittently with interval of about 1 ms, while that in the other ATNL flash propagates downward continuously with a speed at the order of 105 m s-1. In the five classical triggered negative lightning (CTNL) flashes, the propagation speeds of the UPLs vary between 0.35×105 and 7.71×105 m s-1, and the variations of their luminosities and speeds are quite complex during the development processes. Among the four observed natural negative lightning flashes occurred on the land, three have only one return stoke (RS) each and all of their DNLs have many branches with an average speed at the order of 105 m s-1; while the another one has 13 RSs.In the CG flash with 13 RSs, the DNL before the first RS has no obvious branch below 1.4 km above the ground, and its speed ranges from 2.2×105 to 2.3×105 m s-1 between the heights of 0.7 and 1.4 km and exceeds 3.9×106 m s-1 below 0.7 km; preceding the 4th RS, an attempted leader is observed with a speed ranging from 1.1×105 to 1.1×106 m s-1 between 0.8 and 1.5 km. As for the three observed natural negative lightning flashes occurred on the sea, each has only one RS, and each DNL preceding the RS has a few branches, two of which have an average propagation speed at the order of 105 m s-1, and the other of 106m s-1, respectively. All the DNLs contained in the observed natural negative lightning flashes, except the attempted leader, propagate with gradually increasing luminosity and increasing speed in whole.     

2006—2011年广州人工触发闪电

2006—2011年夏季在广州野外雷电试验基地开展了广东综合闪电观测试验 (GCOELD)。试验期间,针对人工触发闪电进行了近距离声、光、电、磁特征等综合测量,对自动气象站电源线和信号线上产生的感应电压特征进行了观测和分析,并对广东省地闪定位网的探测效率和定位精度与人工触发闪电进行了比对和校验。试验结果表明:人工触发闪电回击峰值电流范围为-31.93~-6.67 kA,回击电流波形的半峰宽度的范围为6.18~74.19 μs,10%—90%的上升时间范围为0.24~2.25 μs。触发闪电的上行正先导的发展速度在104~105 m/s量级;人工触发闪电的回击过程在架空电源线路 (1200 m长,2 m高) 上产生的感应过电压可达十几千伏;广东电网闪电定位系统对人工触发闪电事件的探测效率为95%,平均定位误差为759 m,闪电定位系统反演得到的电流峰值与实际测量的电流峰值平均相对偏差为16.3%。     

Fine-resolution simulation of cloud-to-ground lightning and thundercloud charge transfer

2-D 12.5 m-resolution simulations of cloud-to-ground (CG) lightning discharge processes have been performed using an improved stochastic lightning model for different types of cloud charge distributions, such as dipole, tripole, bi-dipole and multi-layer charge structures produced from the numerical simulation of thundercloud electrification. The modelling produced the fine branched channel structure of CG lightning and the results illustrate the relations between CG lightning channel propagation and cloud charge distribution. The simulated features of CG lightning are associated with the observed results. The simulation studies are essential in our understanding of complex charge transfer processes caused by CG lightning discharges in thunderclouds. The induced charges of opposite polarity are deposited or embedded in the local volumes where the bidirectional leaders passed during a CG lightning discharge. Although the embedding affects charge structure only in a pair of significant positive and negative charge regions closest to the ground, the electric field strength acutely weakens and electrostatic energy in thunderclouds is significantly consumed when the discharge terminates. In addition to simulating the upward and downward breakdown of the initial leader to ground and the ensuing return stroke (RS), the simulation assumes that current continues to flow in the channel to ground and determines the upward breakdown until the end of the discharge. For the subsequent discharge sub-process, the upward leader channel tends to transfer the charges with the same polarity as the RS, while the downward leader channel favors transfer of opposite charge to ground. In the sub-processes of a few CG flash simulations, the magnitude of the opposite charges from the downward leader exceeds that of charges with the same polarity from the upward leader so that the net charges transferred to the ground have a reversed polarity to the RS. The simulation presents similar features of CG lightning as those observed in realistic bipolar CG lightning.     

地闪近地面形态特征的数值模拟

该文在已有闪电随机放电参数化方案的基础上,截取近地面区域,保持闪电其他基本参数不变,通过改变闪电的空间形态,对同一背景下的闪电进行多次模拟,研究闪电近地面空间形态的差异对闪电击地点位置、上行先导长度、上行先导触发时下行先导的尖端位置及连接过程形态等参数的影响,并探索闪电参数之间的相关性。结果显示:闪电近地面空间形态会使上行先导长度在77~609 m区间内变化,大部分集中在100~200 m,也会使上行先导触发时下行先导的尖端位置分布在建筑物上空的一个椭球形空间内。同时,闪电近地面空间形态的差异也会使地闪连接形态呈多样性。另外,近地面闪电下行先导长度与上行先导长度有一定的线性相关性,而其他闪电参数相互之间的相关性较弱。这不仅可以加深对闪电空间形态不确定性的理解,同时也对以后的模式建立有一定借鉴意义。     

空中触发闪电的下行先导及其接地行为

１９９６年夏季在江西南昌附进行的人工触发闪电野外实验中,用新开发的不接地的火箭－导线技术成功地在雷暴云下的负环境电场中触发了云对地产偿电。我们用一套成像率为１０００幅／秒的高速数字化摄像系统对下行负先导进行了观测。     

广州高建筑物雷电观测与研究10年进展

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。     

高矮建筑物多上行先导连接过程的数值模拟

运用改进后的三维多先导模型,允许高矮建筑物上均可以始发上行先导,对多次地闪的连接过程进行模拟.结果 表明:矮建筑物始发上行先导和被击中的概率较小,高建筑物对矮建筑物上行先导的始发具有较明确影响.建筑物间的高度差是影响上述连接过程的主要因子,当建筑物间高度差较小时,高建筑物对矮建筑物的屏蔽效应不明显,下行先导通道的相对位...     

人工触发闪电放电过程分析：I.先导放电过程

利用人工触发闪电电场,电流和闪电通道亮度高速摄像观测资料,分析了第一次回击前衔导过程的放电特性,结果指出,对于空中触发,先导传输具有“双向”特征,由于下行先导发展,先导通道电流分布具有不均匀性,连接导线汽化都发生在上行先导阶段。人工闪电第一次回击虽然与自然闪电继后回击特性十分相似,但两者放电特征仍有差别,前者具有曾长的连续电流过程。     

闪电初始阶段和尺度判别方法及其特征

基于LMA三维闪电定位数据,对2004年10月5日发生于美国新墨西哥州的一次超级单体过程的闪电初始及其尺度特征进行研究,提出闪电初始阶段自动判别及其特征参量提取方法,并给出参量分布特征。结果显示:闪电初始阶段上行负先导（下行负先导）的持续时间中值为13.5 ms（7.5 ms）,三维位移中值为1.4 km（1.0 km）,三维平均位移速度中值为9.2×104 m·s-1（1.2×105 m·s-1）,上行负先导速度随时间递减,下行反之,二者与垂直方向夹角的中值分别为40°和54°。表征闪电尺度的闪电凸壳面积和闪电总长度的概率密度呈负幂函数分布,在小值方向分布更为集中。闪电水平延展距离中值为6.1 km,垂直延展距离中值为4.3 km,约83%的闪电其水平延展距离大于垂直延展距离;闪电的持续时间中值为271.0 ms。分析发现,以水平延展为主的闪电起始高度分布峰值位于8.5 km,以垂直延展为主的闪电起始高度分布峰值位于11 km。闪电初始阶段位移方向越接近水平,对应闪电垂直延展越小,说明闪电初始段的传播方向对于闪电垂直延展具有重要影响。     

A review of advances in lightning observations during the past decade in Guangdong,China

This paper reviews recent advances in understanding the physical processes of artificially triggered lightning and natural lightning as well as the progress in testing lightning protection technologies, based on a series of lightning field campaigns jointly conducted by the Chinese Academy of Meteorological Sciences and Guangdong Meteorological Bureau since 2006. During the decade-long series of lightning field experiments, the technology of rocket-wire artificially triggered lightning has been improved, and has successfully triggered 94 lightning flashes. Through direct lightning current waveform measurements, an average return stroke peak current of 16 kA was obtained. The phenomenon that the downward leader connects to the lateral surface of the upward leader in the attachment process was discovered, and the speed of the upward leader during the connection process being significantly greater than that of the downward leader was revealed. The characteristics of several return strokes in cloud-to-ground lighting have also been unveiled, and the mechanism causing damage to lightning protection devices (i.e., ground potential rise within the rated current) was established. The performance of three lightning monitoring systems in Guangdong Province has also been quantitatively assessed.     

A Review of Advances in Lightning Observations during the Past Decade in Guangdong,China

This paper reviews recent advances in understanding the physical processes of artificially triggered lightning and natural lightning as well as the progress in testing lightning protection technologies, based on a series of lightning field campaigns jointly conducted by the Chinese Academy of Meteorological Sciences and Guangdong Meteorological Bureau since 2006. During the decade-long series of lightning field experiments, the technology of rocket-wire artificially triggered lightning has been improved, and has successfully triggered 94 lightning flashes. Through direct lightning current waveform measurements, an average return stroke peak current of 16 k A was obtained. The phenomenon that the downward leader connects to the lateral surface of the upward leader in the attachment process was discovered, and the speed of the upward leader during the connection process being significantly greater than that of the downward leader was revealed. The characteristics of several return strokes in cloud-to-ground lighting have also been unveiled, and the mechanism causing damage to lightning protection devices(i.e., ground potential rise within the rated current) was established. The performance of three lightning monitoring systems in Guangdong Province has also been quantitatively assessed.     

人工触发闪电通道的发光特征

利用成像率为１０００幅／秒的高速数字化摄像系统在３８０ｍ的极近距离对人工触发闪电通道的发光特征进行了观测的研究。人工引发闪电除了采用的火箭地带接地导线的触发方式外还发展导线下端不接地的空中触发闪电的新技术。结果表明,闪电通道的发光截面基本上呈对称型。     

人工引雷上行正先导传播过程中爆发式磁场脉冲极性反转现象的观测与分析

为了进一步理解人工引雷上行正先导的传播过程及相关的爆发式电磁辐射脉冲,本文分析了2014年8月23日山东沾化人工触发闪电实验（SHATLE）中获得的三次上行正先导通道含有明显向下传播过程的个例。结果表明,在初始连续电流阶段观测到的爆发式磁场脉冲极性反转现象与正先导头部发展方向相对于观测位置投影方向的变化密切相关。因此可以推断,爆发式磁场脉冲是由正先导头部较小空间尺度放电过程辐射出的,就本文分析的个例而言,爆发式磁场脉冲辐射源的放电尺度约为2 m,放电强度的最大值达到2.49 kA。爆发式磁场脉冲的辐射机制不同于人工引雷先导始发阶段初始脉冲电流产生的磁场脉冲的辐射机制,可能与正先导通道头部的梯级形式发展过程相关。     

一次多回击触发闪电全过程的连续干涉仪观测

基于自主研发的闪电连续干涉仪,对2019年6月11日在中国气象局雷电野外科学试验基地广州从化人工引雷试验场成功触发的一次多回击闪电放电全过程进行观测,结合通道底部电流数据和电场变化数据,共同揭示触发闪电全放电过程:连续干涉仪能够定位到最小为8 A的不连续的先驱电流脉冲辐射信号,初始先驱电流脉冲(IPCP)的平均转移电荷量约为先驱电流脉冲(PCP)的2倍;上行正先导连续发展后为初始连续电流(ICC)过程,最初正流光通道以105 m·s-1量级的速度继续发展延伸,之后出现反冲先导放电;在ICC阶段出现的经典M分量,可由向前的106 m·s-1量级速度的正流光(先导)产生,也可由已有通道头部产生的反冲先导产生,且整个M分量过程中,多个反冲先导维持了放电过程的持续;之后的回击间过程以反冲先导为主要放电形式,回击电流脉冲之前存在多次反冲先导过程,但多数未发展到接地通道,只处于企图先导阶段,直至成功的先导回击产生;而前两次回击具有超短的时间间隔,约为4.5 ms,这是由于两次回击前的先导来源于云内不同分支的反冲先导过程。     

双向先导正端突然延展现象的高速摄像观测

基于广州高建筑物雷电观测站的观测设备,于2016年6月4日在广州塔上发生的一次上行闪电过程中观测到双向发展的直窜先导正端在回击前、后突然延展的现象。利用高时间分辨率的光学和电场变化同步数据,分析双向先导正端突然延展现象的细节特征。结果表明:回击前直窜先导双向发展时正端可能会出现多次突然延展的现象;突然延展现象有时由双向先导的正端与已有的悬空先导序列相连而引发,并促使双向先导正端传输至未击穿空气中;在一次继后回击后,通道正端头部也观测到两次突然延展现象,但未沿回击前正端伸展通道传输,而是通过开辟新通道进入了未击穿空气;回击前直窜先导正端三次突然伸展的二维平均速率约为2.3×106 m·s-1,伸展长度平均值约为115 m;回击后通道头部两次突然延展的二维平均速率约为4.3×106 m·s-1,伸展长度平均值约为212 m。     

雷击建筑物的先导连接过程模拟

为了研究闪电先导与地物的相互作用,该文建立了一个闪电先导的二维模式以模拟雷击建筑物的先导连接过程。模拟得到梯级长度在13.8～51.5 m的范围内,下行先导的感应电荷为0.03×10~(-4)～1.2×10~(-4) C/m,梯级长度和感应电荷量均随着先导离地高度的下降而增加,模拟结果与观测值相吻合。下行先导最后一跳之前的转向并不明显,但最后一跳,下行先导向避雷针产生的上行先导偏转一定角度。模式模拟了下行先导与40 m宽度的建筑之间的相互作用和连接过程,得到建筑物拐角也具有一定的吸引半径,避雷针和拐角之间存在竞争关系。因此,在雷电防护设计中需要考虑拐角等复杂结构尖端对闪电的吸引作用,简单地采用理想情况(如地面孤立高耸尖端)下避雷针的吸引半径等参数进行复杂建筑物的防雷设计会存在问题和隐患。     

建筑物群中多上行先导三维模型的建立

为实现对地闪过程中多上行先导现象的模拟,在已有三维随机放电参数化方案基础上,植入多先导始发与发展模块以建立高建筑群多上行先导模型,利用电场并行计算技术提高模拟效率。将新模型应用于实际地闪模拟并就统计数据与先导形态特征同观测数据进行对比。结果表明:上行未连接先导长度为12~709 m,起始高度为360~600 m,距连接点水平距离为255~1026 m,距下行先导最近分支的距离为326~589 m,与观测统计结果具有较高的一致性;形态上再现了实际地闪个例F1215中上行未连接先导始发时间早,通道笔直的特点,也能够模拟下行先导与单上行先导头部、单上行先导侧面、多上行先导中连接先导头部、多上行先导中连接先导侧面4种已有观测记录的连接情况,为后续研究提供基础模型。分析模拟结果初步得出结论:最高的广州塔能够对附近一定范围建筑起保护作用且能吸引较远处的下行先导分支;多先导的始发与最后一跳的连接受地面高建筑物群分布、高度以及下行先导位置综合影响。