Fractal-geometry simulation of a lightning discharge

It is suggested that a wideband lightning discharge be approximated by a damped periodic oscillation. With such an approach, the oscillation frequency and relaxation time are introduced and it is found that lightning radiates over a distance of several tens of kilometers. This length is much greater than the lightning bolt’s apparent length (several kilometers). The difference between the lengths is explained using fractal geometry. In terms of fractal geometry, the lightning discharge is so tortuous that an actually very long lightning bolt is accommodated by a short straight line. An attempt is made to determine the fractal dimension of tortuous and intermittent lightning bolts.     

Mechanism of generation of runaway electrons in a lightning leader

A mechanism is analyzed of the electric field enhancement in a lightning leader up to the level permitting runaway of low-energy electrons. The ionization wave propagation in the preionized domain in front of the leader makes it possible to overcome the limitation imposed on the field intensity by transversal expansion of the leader front. By means of numerical simulations, it is demonstrated that, at the final stage of formation of a new leader step, generation of an electric field is possible in the channels of the streamer zone ahead of the new step with intensity sufficient for electron runaway and, consequently, for producing the X-ray and γ-ray pulses observed in correlation with the lightning leader steps.     

Modeling of filament discharge development in a XeCl excimer laser

Dynamics of a filament discharge in a discharge-excited XeCl excimer laser medium has been simulated for a sequence of discharge pulses (shots). In the present model a filament discharge is triggered at a microprotrusion on a cathode surface. After the first discharge initiation, a hot spot is created near the cathode, then filament develops toward the anode in the second shot. Images of the filament discharge development and its properties in a XeCl excimer laser are presented     

一次人工触发闪电上行正先导的传输特征

利用山东一次人工触发闪电的高速摄像和30 m, 60 m和480 m的同步电场测量, 清晰显示了人工触发闪电上行正先导的传输特征.上行正先导头部光强相对较强, 二维发展速度变化波动较大并呈现明显不规则性,表明上行正先导发展具有明显的梯级特征. 在先导开始阶段从340 m到705 m高度之间上行正先导平均发展速度为9.8×10⁴ m/s,起始速度是 3.8×10⁴ m/s,局部速度总体上随高度呈现增加趋势.电场变化在近距离产生有规律的梯级状 变化,记录到的28个梯级相邻梯级间隔变化从14 μs 到 39 μs,几何平均值为25.1 μs. 估计的先导梯级长度分布在0.9 m到3.7 m,几何平均值为1.7 m.先导电场变化由慢的正向梯级状变化和 脉冲变化组成,结合光学和电场变化测量结果,得出正先导头部通道发生弯曲可使其电场变化的梯级特征减弱 或消失;正负先导梯级形成机制可能类似,均由其先导头部前端的双向流光发展而来.     

Statistical model of the lightning leader attraction to ground objects

A statistical model of the lightning channel attraction to ground objects is proposed based on the analysis of the available experimental data on the breakdown of long air gaps and the propagation of the lightning leader channel. The model allows one to estimate the probability of lightning interception by a lightning rod and of lightning damage of the protected object. Examples of calculating the probabilities of lightning strike to the lightning rod and neighboring areas are presented.     

Study of the leader of a spark discharge over a water surface

This paper discusses an experimental study of the leaders of incomplete spark discharges with a capacitance of 0.1 and 1 μF over a water surface when the initial voltage is 3–6 kV in discharge gaps 8 and 22 cm long, having side branches and without branches. The distributions of the field, the current, the current density, the conductivity, and the electron concentration along the leader have been determined, as well as the changes in the velocity and length of the leader as it evolves. It has been established that the evolution of the leader has a self-maintained character, and that the product of the storage capacitance and the initial potential difference between the head of the leader and the water surface is an invariant of its spatial evolution. Zh. Tekh. Fiz. 68, 44–50 (July 1998)     

Radio emission structure of cloud-to-ground lightning discharge

Cloud-to-ground lightning discharge radio frequency emission is analysed on the base of measurements with high temporal resolution allowed to fully resolve its structure. Discharge radio emission mainly consists of independent random bi-polar pulses. Pulse length, amplitude and interpulse period distributions are studied at different stages of lightning discharge. The significant change of radio frequency emission structure during discharge development is demonstrated.     

人工引发雷电先导-回击过程的电场变化特征

 2005年夏季在山东滨州进行了以人工引发雷电为主的综合观测实验，在负电场环境下，成功引发雷电5次，其中传统引发方式3次，空中引发方式2次。详细分析了双向先导-小回击过程和箭式先导-回击过程的垂直电场变化特征。结果表明：2次空中引发雷电的双向先导发展过程在地面60 m处产生的电场变化为4.70~14.60 kV/m，呈负向变化；在550 m处为0.11~0.16 kV/m，呈正向变化。利用60 m处的先导电场变化，估算双向先导电荷线密度分布的斜率为(1.2~3.8)×10^-7 C·m^-2。箭式先导-回击电场变化波形呈不对称V形，V形的底部对应先导的结束和回击的开始。60和550 m处的箭式先导电场几何平均值分别为17.80和1.20 kV·m^-1。随水平距离的增加，箭式先导电场以水平距离的-1.18次方衰减。     

From an electron avalanche to the lightning discharge

The goal of this work is to describe qualitatively the physics of processes which begin with an electron avalanche and finish in a lightning discharge. A streamer model is considered that is based on studies of the recently discovered processes occurring in the prestreamer region. The investigation and analysis of these processes enabled making the conclusion that they are, in essence, the attendant processes, which ensure the electron avalanche-to-streamer transition, and may be interpreted as a manifestation of properties of a double charge layer exposed to the external electric field. The pressing problems of physical processes which form a lightning discharge are considered from the standpoint of new ideas about the mechanism of the streamer formation and growth. Causes of the emergence of coherent super-high-frequency radiation of a leader and the neutron production in a lightning discharge are revealed that have not been explained so far in the theory of gas discharge. Based also on new ideas about the lightning discharge, a simple ball-lightning model, providing answers to almost allquestions formulated from numerous observations on the behavior of ball lightning, is offered, and the need of a new design of lightning protection instead of the traditional rod is discussed.     

飞秒激光引导闪电的模拟实验研究

采用能量40 mJ，脉冲宽度50 fs的超短脉激光脉冲形成的等离子体通道诱发和引导了3—23 cm长间隙的静态高压放电.实验观测显示，等离子体通道整体上能使空气间隙的击穿阈值降低到自然击穿阈值的40％.实验中通过对放电电弧发出的白光信号与激光信号的时间延迟进行分析得到激光引导下梯级先导的发展速度约为10⁷ cm/s. 关键词： 等离子体通道 高压放电     

Various features of VLF waves generated by lightning discharge

Summary Using the well-accepted features of lightning discharge, we have studied certain aspects of electromagnetic-wave generation, frequency spectrum and polar characteristics of these radiations. The effect of conducting ground and ionospheric layer on the attenuation of VLF signal is discussed. The likely role of the verticality of cloud-to-ground discharges and the horizontality of cloud-to-cloud discharges in launching of VLF waves and governing the occurrence and overall morphology of whistlers is discussed.

---

Riassunto Usando le caratteristiche accettate della scarica del fulmine, sono stati studiati alcuni aspetti della generazione di onde elettromagnetiche, lo spettro di frequenza e le caratteristiche polari di queste radiazioni. Si discute l'effetto del terreno conduttore e dello strato ionosferico sull'attenuazione del segnale VLF. Si discute il ruolo probabile della verticalità delle scariche dalle nuvole alla terra e dell'orizzontalità della scariche tra nuvole nel lancio di onde VLF e nel regolare il verificarsi e la morfologia globale dei sibili.

---

Резюме Используя хорошо известные особенности разряда молнии, мы исследуем некоторые аспекты образования тлектромагнитных волн, частотный слектр и характерисики поляры этого излучения. Обсуждается влияние проводимости земли и ионосферного слоя затухание VLF сигнала. Обсуждается роль вертикаляности разрядов между облаком и землей и горизонтальностью разрядов между облаками при возбуждении VLF волн и при определении появления и полной морфологии свистящнх атмосфериков.

     

Main stage of the lightning discharge: Mechanism and output characteristics

Physical processes responsible for the lightning discharge are considered. An expression relating the basic physical quantities describing the evolution of the lightning discharge to the magnitude and waveform of the lightning current is found. It is shown that the peak lightning current is proportional to the lightning channel length, the steepness of the current pulse depends on the physical constants of the spark discharge, and the current pulse duration depends on the physical constants of the spark discharge and also on the leader’s space charge density.     

Modeling of corona under positive lightning surges

A novel corona model for predicting the corona characteristics under positive lightning surges is proposed. The ionization process is described by a series of successive generations of electron avalanches. A simplified method is presented for computing the electric field in the ionization zone. With a discrete treatment for the ionization process in time and space, the proposed model computes the total charge of corona from the applied surge voltage and so the q–u curves can be obtained. A laboratory measurement of q–u curves is also made by a coaxial cylindrical electrode to check the validity of the proposed model.     

基于干涉仪原理的闪电先导VHF辐射源速度测量

简述了闪电VHF辐射源窄带干涉仪定位原理及其数据处理方法,利用改进的窄带干涉仪系统对闪电先导VHF辐射源进行定位,给出了闪电放电通道的时空结构,并结合电场变化资料和声光差记录,估算了闪电先导放电发展的速度.     

负地闪CPT放电事件的发生规律研究

本文分析了2012年广州地区6次雷暴过程的负地闪中不规则脉冲簇(chaotic pulse trains,CPT)放电事件的发生规律.结果表明:CPT是负地闪整个放电过程中普遍存在的放电现象,在323次负地闪中有243次出现了CPT放电事件,比例达到了75.2%,并且能够发生在负地闪的首次回击之前、回击之间以及最后一次回击之后,其中有66.7%的继后回击之前和11.5%的最后一次回击之后发生了CPT.研究也发现,CPT在继后回击之前有四种分布类型:单独出现一次CPT-c(与继后回击相连的CPT)、单独出现一次CPT-i(与继后回击有一定时间间隔的CPT)、同时出现CPT-c和CPT-i以及同时出现多次CPT-i,其中,单独出现一次CPT-c类型最为多见,39.4%的继后回击之前为此类型,而在第一次和第二次继后回击之前更容易出现多次CPT的现象,分别占到对应次序回击总数的9.4%和7.7%.而随着继后回击次序的增加,其之前发生CPT的概率呈减小的趋势,并且除了第一次和第二次继后回击以外,其他继后回击之前CPT-c的出现频次大于CPT-i.另外,CPT-i和最后一次回击之后的CPT均叠加在K变化上,部分回击间的CPT也能够发生在J过程中.     

Self-sustained relativistic-runaway-electron avalanches in the transverse field of lightning leader as sources of terrestrial gamma-ray flashes

The possibility of the development of self-sustained discharge in the transverse electric field of the lightning leader in the mode of generating relativistic-runaway-electron avalanches, supported by positive relativistic feedback with the participation of high-energy bremsstrahlung and positrons generated by the avalanches themselves, is analyzed. For a cylindrical geometry of the leader, the threshold of switching on the feedback was shown to be rather low. It was demonstrated that the discharge may be the source of pulses of penetrating emissions observed in the correlation with thunderstorm activity, the characteristics of which are well reproduced in the cylindrical-leader model. The penetrating emissions generated in the vicinity of the leader may be dangerous to the electronic equipment of aircrafts, as well as airplane passengers and crews.     

Recoil leader formation and development

The existing interpretation in the lightning literature, based on field measurements, defines recoil leaders as negative leaders. However recoil leaders are floating conductors, and, based on this physical assumption, they should be defined as bipolar and bidirectional leaders. This physics-based assumption has never previously been verified experimentally. Such verification, reported in this paper, has been obtained from observations of branched upward positive leaders from a tall tower using a high-speed video system synchronized with electric and magnetic field change and luminosity measurements on the ground. The analysis of these observations clearly reveals the nature of recoil and dart leaders as bidirectional and bipolar electrodeless discharges that develop from a small region along a path of the decayed channels of a previous positive leader, or a positively charged return stroke of negative CG flashes.     

Modeling of the electrostatic corona discharge reactor

A model is presented for the electrostatic corona discharge reactor (ECDR) in a pin-plate configuration. The main objective is to describe the fundamental chemistry and physics governing the discharge behavior and to predict the ECDR performance under various operating conditions. The electric field strength is estimated assuming a space-charge-free field. A two-term spherical harmonic expansion is used to solve the Boltzmann equation for the electron energy distribution function (EEDF) and calculate the electron-molecule reaction rates using collision cross-section data. Species continuity equations are solved for the dry and wet air systems to predict ozone and NO_x at various feed flow rates (1630, 4890, 14, 670 cm/s) and an applied voltage of 10 kV. Among the various results reported, it is noted that the calculations indicate the Maxwell EEDF cannot be used because it overpredicts the electron-molecule rate coefficients by several orders of magnitude     

Space-time-dependent development of the plasma in a pulsedhollow-cathode discharge

The fast (nanosecond) breakdown of hollow-cathode discharges is studied. Streak camera investigations are presented on the space-time-dependent development of pulsed discharges, starting from low-current preionization discharges. The discharges start near the entrance to the cathode, then move further back into the cathode, and then spread over a wider range along the axis of the cathode. The depth range of the intense pulsed hollow-cathode plasma was found to be two to eight times the cathode diameter     

微波阶梯阻抗变换器低气压电晕放电粒子模拟

采用3维粒子软件VORPAL对微波阶梯阻抗变换器中的低气压电晕放电过程进行了粒子模拟,获得了放电过程中带电粒子实空间分布的时间演变图像,分析并解释了其中低气压电晕放电机理和微放机理之间的关系.模拟结果表明:低气压电晕放电的阈值电压随着气压的增长呈现先减小后增加的变化趋势;并且随着气压的增长,微放电作用减弱,低气压电晕放电作用增强.通过对银和铜两种器壁材料放电阈值的比较,获得了两种放电机理之间的临界气压.