Waveshapes of continuing currents and properties of M-components in natural positive cloud-to-ground lightning

This work analyses the waveshapes of continuing currents and parameters of M-components in positive cloud-to-ground (CG) flashes through high-speed GPS synchronized videos. The dataset is composed of only long continuing currents (with duration longer than 40 ms) and was selected from more than 800 flashes recorded in São José dos Campos (45.864°W, 23.215°S) and Uruguaiana (29.806°W, 57.005°S) in Southeast and South of Brazil, respectively, during 2003 to 2007 summers. The videos are compared with data obtained by the Brazilian Lightning Location System (BrasilDAT) in order to determine the polarity of each flash and select only positive cases. There are only two studies of waveshapes of continuing currents in the literature. One is based on direct current measurements of triggered lightning, in which four different types of waveshapes were observed; and the other is based on measurements of luminosity variations in high-speed videos of CG negative lightning, in which besides the four types above mentioned two additional types were observed. The present work is an extension of the latter, using the same method but now applied to obtain the waveshapes of positive CG lightning. As far as the authors know, this is the first report on M-components in positive continuing currents. We also have used the luminosity-versus-time graphs to observe their occurrence and measure some parameters (duration, elapsed time and time between two successive M-components), whose statistics are presented and compared in detail to the data for negative flashes. We have plotted a histogram of the M-components elapsed time over the total duration of the continuing current for positive flashes, which presented an exponential decay (correlation coefficient: 0.83), similar to what has been observed for negative flashes.     

Continuing current in multiple channel cloud-to-ground lightning

In this study we analyze the effects of continuing current initiated by strokes following a new channel to ground in multiple stroke flashes using high-speed video records, electric field measurements from a fast antenna and lightning detection network data. We observed that the long continuing current initiated by a stroke that follows a new channel also obeys the pattern in the initiation of long continuing current suggested by Rakov and Uman [Rakov, V.A., Uman, M.A., 2003. Lightning: Physics and Effects, 687pp., Cambridge Univ. Press, New York.]. We also verify that the statement of Rakov and Uman [Rakov, V.A. and Uman, M.A., 1990. Some properties of negative cloud-to-ground lightning flashes versus stroke order, Journal of Geophysical Research. 95, 5447–5453.] reporting that: “...strokes initiating long continuing currents tend to have lower initial electric field peak than regular strokes” is valid for strokes that create a new channel to ground and are followed by long continuing current (CC). Apparently the reduction of peak current value (I_p) when the stroke is followed by a long CC is stronger than the I_p increase that is commonly observed when strokes follow a new channel. We also find that the “exclusion zone” proposed by Saba et al. [Saba, M.M.F., Pinto, O. Jr., Ballarotti, M.G., 2006a. Relation between lightning return stroke peak current and following continuing current, Geophysical Research Letters 33, L23807, doi:10.1029/2006GL027455.] is valid for new channels initiating CC, and finally we verify that a number of strokes in the same channel larger than four or the existence of a long CC current do not always consolidate the channel in a multiple stroke flash.     

Transient currents in the global electric circuit due to cloud-to-ground and intracloud lightning

Intracloud (IC) and cloud-to-ground (CG) lightning flashes produce transient changes in the electric field (E) above a thundercloud which drive transient currents in the global electric circuit (GEC). Using in-cloud and above-cloud E data from balloons, ground-based E data, and Lightning Mapping Array data, the above-cloud charge transfers due to lightning transients are estimated for five IC and five CG flashes from four thunderstorms that occurred above the mountains in New Mexico, USA, in 1999. For the five CG flashes (which transferred − 4 to − 13 C to the ground), the transient currents moved + 1 to + 5 C of charge upward from cloudtop toward the ionosphere, with an average transient charge transfer of about 35% of the charge transferred to ground. For the five IC flashes (which neutralized 6 to 21 C inside the cloud), the transient currents moved − 0.7 to − 3 C upward, with an average transient charge transfer of about 12% of the lightning charge. Estimates for three thunderstorms indicate that the transient currents made only a small GEC contribution compared to the quasi-stationary Wilson currents because of the offsetting effects of IC and CG flashes in these storms. However, storms with extreme characteristics, such as high flash rates or predominance of one flash type, may make a significant GEC contribution via lightning transients.     

Luminosity characteristics of leaders in natural cloud-to-ground lightning flashes

Using high-speed cameras, we have recorded the leaders contained in four natural negative cloud-to-ground (CG) lightning flashes in the summers of 2006 and 2007 at Conghua, Guangdong, China. It was found that the downward negative leaders preceding the first return stroke could propagate at quite different speeds. In one flash, the average speed of the downward negative stepped leader with no branches is about 2.2 × 10⁶ m s^− 1, while that of the other 3 flashes are all of the order of 10⁵ m s^− 1 with multilevel branches. The luminosity of the leaders shows an increasing tendency in propagating downward to the ground. For the leaders preceding the subsequent strokes, although all of them exhibit high speeds as reported previously. One subsequent leader exhibits an increasing speed from 5.2 × 10⁵ m s^− 1 to 1.7 × 10⁶ m s^− 1 during its propagation from about 1.26 to 0.36 km above the ground, and its luminosity also increased. The speed and luminosity of a leader between subsequent strokes of a natural lightning appear to decrease as it developed downward. Its speed ranges from 1.1 × 10⁶ to 1.1 × 10⁵ m s^− 1, with a height between 1.15 and 0.81 km above the ground.     

深圳云地闪时空分布特征研究

利用1997-2011年云地闪电定位探测资料和深圳国家基本气象站1953-2011年的观测资料,对深圳云地闪电（简称地闪）时空分布特征和雷暴日变化趋势进行分析。结果表明：深圳雷暴日数近59 a来呈下降趋势,小波分析显示年雷暴日数存在5 a周期和10-15 a的次周期;年内地闪频次特征表现为6月和8月双峰形特征,8月为全年地闪次数最多的月份;雷暴的活跃程度与太阳辐射热力条件密切相关,地闪活动高峰出现在14-18时;深圳地闪密度呈现西北多、东南少,内陆地区多、沿江沿海地区少的分布特征,地形、海陆分布是影响地闪空间分布的重要原因;地闪强度的分析表明,正、负闪月平均强度峰值分别出现在2月和6月,负闪强度低于正闪,正、负闪日强度峰值均未出现在频次峰值时段。     

Characteristics of cloud-to-ground lightning in warm-season thunderstorms in the Central Great Plains

In July 2005, a field campaign was conducted in the Central Great Plains to obtain 60-field/s video imagery of lightning in correlation with reports from the U.S. National Lightning Detection Network (NLDN) and broadband electric field waveforms from the Los Alamos Sferic Array (LASA). A total of 342 GPS time-stamped cloud-to-ground (CG) flashes were recorded in 17 different sessions, and 311 (91%) of these were correlated with reports from the NLDN. Only 6 of the 17 recording sessions were dominated by flashes that lowered negative charge to ground, and 11 were dominated by positive CG flashes. A total of 103 flashes recorded on video were correlated with at least one NLDN report of negative CG strokes, 204 video flashes were correlated with one or two positive stroke reports, and 4 had bipolar reports. In this paper, we will give distributions of the estimated peak current, I_p, as reported by the NLDN, of negative and positive first strokes that were recorded on video, the multiplicity of strokes that were recorded on video, and the number of ground contacts per flash that were resolved on video. 41 (40%) of the negative flashes produced just a single-stroke on video, and 62 (60%) showed two or more strokes. The observed multiplicity of negative flashes averaged 2.83, which becomes about 3.14 after correcting for the finite time-resolution of the video camera. 195 (96%) of the positive flashes produced just a single-stroke on video, and 9 (4%) showed two strokes; therefore, the observed multiplicity of positive flashes averaged 1.04. Five out of 9 (56%) of the positive subsequent strokes re-illuminated a previous channel, and 4 out of 9 (44%) created a new ground contact. Simultaneous video, LASA, and NLDN measurements also allowed us to examine the classification of NLDN reports during 3 single-cell storms (one negative and two positive). Based on the LASA waveforms, a total of 204 out of 376 (54%) NLDN reports of CG strokes were determined to be for cloud pulses. The misclassified negative reports had |I_p| values ranging from 3.8 kA to 29.7 kA, but only 58 (24%) of these had |I_p| > 10 kA, and only one misclassified positive report had I_p > 20 kA. Radar analyses showed that most of the negative and positive CG strokes that were recorded on video were produced within or near the convective cores of storms. The radar imagery also showed that single-cell storms tended to produce one polarity of CG flashes at a time, and that such storms could switch rapidly from negative to positive CG flashes when the reflectivity was near maximum. Multiple-cell storms produced both negative and positive flashes over a broad region, but each polarity tended to cluster near regions of high-reflectivity.     

Simultaneous optical and electrical observations on the initial processes of altitude-triggered negative lightning

Using a high-speed camera system and two electric field antenna systems, we have documented the initial processes of an altitude-triggered negative lightning (ATNL). The optical records clearly show that ATNL begins with the inception and propagation of an upward positive leader (UPL) and then a simultaneous propagation of UPL and downward negative leader (DNL), known as the bidirectional leader process, follows. Based on the optical records, it is inferred that (1) the triggering height is about 371 m; (2) the two-dimensional (2D) propagation speed of the UPL in its inception phase is about 3.8–5.5 × 10⁴ m s^− 1 during its propagation from about 393 to 452 m above the ground; (3) the grey levels of the DNL are about one order of magnitude higher than that of the UPL in their inception phase; (4) a discharge phenomenon propagating along the elevated triggering wire part of the lightning channel occurs after the mini-return stroke (MRS), with a 2D propagation speed of about 1.6–2.0 × 10⁵ m s^− 1. Combined with the simultaneous electric field change records, it is further inferred that (1) the UPL incepts about 932 μs earlier than the unstable DNL and about 4.1 ms earlier than the stable DNL; (2) the unstable DNL propagates downward intermittently three times with a time interval of about 1 ms, and each propagation contains a different number of steps with an average step length of about 7 m; (3) the stable DNL incepts at the tip of the unstable one, with a 2D propagation speed of about 1.9 × 10⁵ m s^− 1, an average step length of about 3 m, and a stepping time interval varying from 6 to 31 µs with a mean value of 15 µs.     

2011—2019年安徽南部山区与北部平原闪电分布特征

利用2011年1月至2019年12月安徽省ADTD闪电定位系统监测资料,对安徽南部山区与北部平原的闪电频次、极性、雷电流强度等参数进行对比分析。结果表明：安徽南部山区总闪电频次约为北部平原的2.84倍,北部平原正闪比高于南部山区,这与两地区强对流天气类型有关。两地区闪电频次的月、日变化均呈单峰分布,春季、夏季闪电活动明显多于秋季、冬季,午后至傍晚为一天中的雷电活跃时段,但南部山区在雷电高发月份及时段的闪电频次波动程度远大于北部平原。在雷电流强度方面,北部平原整体上大于南部山区,正、负地闪强度分别高出10.77 kA、9.52 kA,其中正地闪强度峰值均出现在2月,负地闪均为10月,南部山区正、负地闪及北部平原负地闪日强度峰值与频次峰值时段相反。对安徽省总闪频次进行主成分分析表明,EOF分解的前5个特征向量累计方差贡献达到59.137%,空间上表现出安徽南部山区与北部平原雷电活动变化趋势既具有一致性,也具有明显的南北差异。     

2011—2019年中国长江三角洲区域闪电时空分布特征

利用2011—2019年江苏、浙江和安徽27个探测站ADTD闪电监测定位系统获取的资料,对中国长江三角洲三省一市(上海、江苏、浙江、安徽)一体化协同发展区域云地闪的发生频次、强度进行统计,运用EOF方法分析闪电频次的空间分布特征.结果表明:中国长江三角洲区域负闪数均占总闪数的95％以上,正闪平均强度均大于负闪平均强度绝...     

2010—2018年辽宁省雷电流幅值特征分析

基于辽宁省2010—2018年闪电定位(ADTD)资料,运用统计学方法分析了雷电流幅值时间变化特征;运用规程计算公式和IEEE推荐公式分别计算了雷电流幅值累积概率密度,并和实际地闪雷电流幅值累积概率密度曲线做了对比分析;运用最小二乘法拟合了IEEE推荐公式.结果表明:2010—2018年辽宁省地闪以负闪为主,占比高达8...     

天津地区雷电流幅值及累积概率分布特征

为研究天津地区雷电流幅值特征,选取2008—2018年ADTD闪电定位数据,研究分析了雷电流幅值时间分布特征和累积概率分布特征。结果表明:天津地区11 a间共计发生闪电106474次,负闪占比89.26%,远高于正闪;雷电流幅值主要集中在2—100 kA,占闪电总数的97.76%,160—200 kA范围内的闪电次数较少,平均正闪电流强度明显大于负闪电流强度;雷电流强度季节特征较为显著,正闪雷电流强度呈双峰分布,负闪雷电流强度分布较为平均,春季正闪活动频繁,秋季次之,夏季负闪频发,冬季雷电活动发生较少,以正闪居多;雷电流高于25 kA时,正闪电流幅值累积概率显著高于负闪,低于25 kA时,负闪电流幅值累积概率高于正闪。负闪电流幅值的累积概率分布与总闪更为接近,与正闪分布差异显著,闪电总数电流累计概率分布主要受负闪影响。通过对比分析发现IEEE工作组(电气与电子工程师协会)推荐的累积概率分布函数更适合于天津地区,特别是雷电流幅值在25—55 kA范围内时,累积概率与推荐公式基本相同。将天津地区雷电流幅值累积概率公式尝试应用于雷电灾害风险评估中,可为精准确定雷电灾害风险评估参数P_(B)取值,精确计算雷击建筑物损失风险提供参考。     

Comparison of lightning activity and radar-retrieved microphysical properties in EULINOX storms

A combined analysis of microphysical thunderstorm properties derived by C-band polarimetric Doppler radar measurements and lightning observations from two ground-based systems are presented. Three types of storms, a multicell, a supercell, and a squall line, that were observed during the European Lightning Nitrogen Oxides project (EULINOX) are investigated. Correlations are sought between the mass of rain, graupel, hail, and snow derived form radar observations at different height levels and the electrical activity, represented either by cloud-to-ground or intracloud flashes. These relationships are explained by connecting the radar-derived properties with the non-inductive charging process. For the multicell and the supercell storm, the lightning activity can be linearly correlated to both the hydrometeor total mass and class specific mass in the upper part of the storm. It is shown that the fractions of graupel and hail above the −20 °C-level in these storms positively correlate with the intracloud flash activity in the supercell, and negatively for the cloud-to-ground lightning frequency in the multicell. No such relation can be established for the squall line, indicating that the convective organization plays a crucial role in the lightning development. The analysis of the masses in the different storms shows that lightning activity cannot be parameterized by total mass alone, other parameters have to be identified. The results provide important information for all lightning studies that rely on bulk properties of thunderstorms, e.g., the parameterization of lightning in mesoscale models or the nowcasting of lightning by radar.     

首次回击具有双接地点的地闪光学和电学特征的个例分析

利用成像率为1000幅／s的数字化高速摄像系统和时间分辨率为1μs的快、慢天线闪电电场变化测量仪在广州附近观测到一次首次回击具有两个接地点的负极性地闪。两个分支到达地面的时间间隔约为30μs;在发生回击R2时,其中一个分支的直窜先导发展成为企图先导。观测发现M一分量的发光要比梯级先导强;回击间的K一变化与云中的在击穿和通道的延伸有关,但不引起云地间通道的发光。光学和电场变化的同步观测证实了直窜一梯级先导的发展速度与前一次回击的时间间隔有关,较快的先导发展速度对应于较短的回击时间间隔,较慢的发展速度对应于较长的回击时间间隔。另外,本文在资料分析的基础上,提出了产生双接地点的四种可能原因。     

2007—2019年湖北省地闪分布特征及雷电强度等级划分

根据2007—2019年地闪监测资料,采用数理统计方法,分析湖北省闪电活动时空分布特征,融合地闪密度和雷电流强度,提出雷电强度的概念,并完成湖北省雷电强度等级划分。结果表明：湖北省以负极性闪电为主,占94.7%,平均正地闪强度为50.2 kA、负闪36.0 kA、总闪37.0 kA。闪电活动主要集中在全年的3—9月、全天的14—20时,闪电活动较弱的月份、时段发生正地闪的比例较高。正地闪强度月变化大致呈“V”型,总闪电和负地闪强度逐月波动变化。雷电流强度日变化主要呈单峰单谷型,正地闪强度09时最大,15时最小,总闪电和负地闪13—14时雷电流强度最小,05时最大。地闪密度和雷电流强度存在地域性差异,整体呈东高西低分布特征。湖北省雷电强度可划分为高、中、低3个等级,高值区主要位于湖北东部的大别山、幕阜山与江汉平原交汇地带以及湖北西部山区向江汉平原的过渡地带;湖北西南、湖北西北以及湖北个别边缘区域雷电强度等级较低;中值区主要分布在湖北中部平原一带。     

湖北黄冈地区2006～2011年闪电时空分布特征分析

利用湖北省2006—2011年13个ADTD站的闪电定位资料,对黄冈地区的闪电频次、电流强度与极性等方面的时空分布特征进行分析。结果表明,黄冈地区以负闪电为主,负闪电占总闪数的97.4%,平均闪电强度为37.59 kA;正闪电仅占总数的2.6%,平均闪电强度47.36 kA。正、负闪电的发生频次有明显的日变化和季节变化特征。闪电频次的日变化呈双峰值型,高峰值出现在16时与19时。季节变化呈明显单峰值特征,4—9月闪电次数占总闪数的94.6%,其中6—8月占83.6%。闪电高密度区主要集中于黄冈中部的黄州、团风、浠水及罗田南部地区,密度值普遍在80次(/25 km2.a)以上。雷电流强度值主要集中在10～60 kV之间,占总次数的89.1%。     

1971—2008年青岛地区雷电时空分布特征

选取1971—2008年青岛地区7个地面观测站雷暴日资料和2006—2009年闪电定位系统监测资料,统计分析青岛雷暴的时空分布规律,并以某大型石化项目为例,分析了该区域地闪的分布特征。结果表明：近38 a青岛地区雷暴日空间分布自东南向西北逐渐增多,季节性分布特征明显,主要集中在7月和8月。根据闪电定位资料,借助分析软件...     

1971—2008年青岛地区雷电时空分布特征

选取1971—2008年青岛地区7个地面观测站雷暴日资料和2006—2009年闪电定位系统监测资料,统计分析青岛雷暴的时空分布规律,并以某大型石化项目为例,分析了该区域地闪的分布特征。结果表明：近38 a青岛地区雷暴日空间分布自东南向西北逐渐增多,季节性分布特征明显,主要集中在7月和8月。根据闪电定位资料,借助分析软件得出该石化项目附近雷电流强度分布图和雷电流累积概率分布曲线,进而得出对应的雷电流强度值,最大值为41.68 kA。利用闪电定位系统提供的地闪次数计算地闪密度Ng比用人工观测资料计算的结果更为客观,研究结果可为雷电灾害风险评估提供评估参数。     

２００６—２００９年江苏省地闪特征分析及应用

根据2006-2009年江苏省气象部门闪电定位系统资料,对江苏省地闪的总体特征、雷电流强度和地闪的时空分布特征进行了分析,并利用江苏13市雷暴日观测记录,统计了各市地闪密度公式.结果表明,江苏省以负地闪为主,正地闪的平均雷电流强度大干负地闪;地闪随时间变化明显,空间分布和地形密切相关,地闪密集区域应相应加强防雷工作;装设接闪器的建筑物也有遭受雷击的可能,江苏97.75%的地闪的雷电流强度都集中在100 kA以下;各市使用本地化的地闪密度计算公式比IEC公式计算得出的结果更符合实际.     

2007年丹东和阜新地区地闪特征

针对2007年辽宁地闪资料进行分析。结果表明：丹东和阜新是辽宁南北两个地闪高发区,其地闪变化既有共同之处,也有差异点。两地均为负地闪次数远远多于正地闪次数,正闪比相差不大;正闪比春季大,夏季少;丹东平均正、负地闪峰值电流强度均值大于阜新。地闪多发于午后到夜间,丹东多发于早晨。定义了地闪持续时数,分析发现地闪多集中发生在持续6h及以上的地闪活动过程中,因而持续6h及以上的地闪活动过程潜在危害较大。丹东地闪活动易发月份为5-10月,阜新为5-8月;丹东地闪活动最活跃期为8月,阜新地区为7月。     

不同天气类型短时强降水与地闪特征分析

选取2006—2013年山东8次典型短时强降水（降水强度>20 mm·h-1）个例,并根据降水的天气尺度影响系统分为4种类型,利用山东区域ADTD型闪电定位仪资料,统计各类短时强降水与地闪相关性;结合地闪频数、密度分析地闪与短时强降水的雨强、出现时间、空间分布等特征的相关性。结果表明：1）各类强降水与不同范围地闪的相关性不同,与固定范围内地闪的时间、空间分布特征不同;其中负地闪占绝大多数,正闪比例小,负闪占比越大降水越强;站点周边30 km范围内地闪频数与降水相关性较好,低槽冷锋型强降水与地闪频数相关性最好,其次是低涡切变线型,黄淮气旋型短时强降水与地闪频数相关性差,热带气旋型强降水则与正闪相关性更好。2）地闪频数只对单次过程降水量变化有所指示,不能直接用来判别短时强降水,而地闪频数峰值对于短时强降水预报有一定指示意义;其中后倾型低槽冷锋、西北涡、西南涡型短时强降水地闪频数峰值对于预报短时强降水指示意义较强,冷切变和暖切变型指示意义较小,前倾型低槽冷锋、黄淮气旋、热带气旋型无明显指示意义。3）高地闪密度与短时强降水落区对应较好,但短时强降水并不一定会出现在高地闪密度中心区域;大部分短时强降水极值站高地闪密度中心对应;对于后倾型低槽冷锋、暖切变、西南涡型短时强降水,5次·（10 km）-2·h-1可作为预报参考阈值。