Physical processes during development of upward leaders from tall structures

The objective of our study was to identify and interpret the various processes during development of upward positive leaders from tall structures. We provide a physical interpretation for the varying luminosity of the leader channel during its initial ascent and the pulsing luminosity during much later stages of the established leader. Our analysis confirms that pulsed luminosity is a result of recoil leaders intercepting the current-carrying channel connected to ground. This interception produces an M-component. Applying the bidirectional leader concept and a simplified electrostatic approximation, we introduce physical models of the dart leader-return stroke sequence and the M-component.     

On the interception of lightning flashes by power transmission lines

The design of the lightning protection system LPS of transmission lines is based on the well known electro-geometrical model. The electro-geometrical model assumes that the first point on a power transmission line that will come within striking distance of the tip of a down-coming stepped leader channel is the strike point of the lightning flash. The model neglects almost all of the physics associated with the lightning attachment.Nowadays, as it is possible to use modern hardware and software tools and several different numerical methods, it is feasible to apply the physics of the discharge process to the study of lightning attachment. Such models take into account the movement of the downward and the resulting upward leaders from different points on the structures under consideration.In this paper, a procedure based on lightning physics was used to analyze the lightning attachment phenomena in EHV transmission lines of 230 kV and 500 kV and the results were compared with the predictions of the electro-geometrical method.     

Characteristics of lightning flashes striking the CN Tower below its tip

It has been observed that tall structures are sometimes struck by lightning below their tops. This phenomenon necessitates the use of special procedures for the protection of tall structures from lightning hazards. This paper focuses on the analysis of lightning flashes that struck the CN Tower below its tip over an extended period of time (1991–2005). Through the use of video images recorded during the reporting period, it was found that out of 404 flashes to the tower, only 16 hit the tower below its tip (3.96%). The distance between the tower's tip and the strike location varied from 5.4 to 70 m. Statistical analysis of flash characteristics of strikes below the tower's tip generally shows that the flash duration and the number of strokes per flash are considerably lower than those for the majority of cases, when the tower is struck at its tip. Furthermore, a trend of decrease in flash duration is found as the distance between the tower's tip and the strike location increases. Therefore, based on the analysis of the available data, lightning strikes below the top of a tall structure do not seem to pose greater danger than strikes to the structure's top, assuming that the structure is also protected along its sides. It is hoped that the presented observations and statistical analyses will be of value in the development of sophisticated measures against lightning hazards at elevated objects.     

Physical nature of Ball lightning

Physical effects responsible for existence of Ball lightning are considered. It is shown that Ball lightning can be a pure optical phenomenon where only an intense light and compressed air interact. An anomalous great light intensity and light lifetime within Ball lightning are analyzed.     

Physical processes underlying the development of shear turbulence

A physical model of the development of turbulence in free shear flows is proposed. The model is based on the results of numerical simulations of turbulent flow development. The main ideas of the proposed theory of turbulence are stated as follows: the onset of turbulence begins with the formation of large vortices; spectral energy transfer involves both direct and inverse cascades; and the inertial range of the energy spectrum develops as a result of concurrent direct and inverse cascades. The dominant physical factors that determine the spectrum include Joukowski forces.     

Physical mechanisms for the development of lightning discharges between a thundercloud and the ionosphere

An investigation is made of the influence of changes in atmospheric pressure with altitude and the thundercloud geometry on the development of lightning propagating upward to the ionosphere. It is shown that the mechanism for the development of high-altitude lightning does not differ from that for the formation and propagation of ordinary lightning between a thundercloud and the ground. It is established that high-altitude lightning forms as a result of a reduction in pressure with altitude and can only take place from thunderclouds located at high altitudes. Zh. Tekh. Fiz. 69, 134–137 (April 1999)     

闪电光电信号的同步观测与闪电类型模式识别

 利用宽带电场仪和光学纹波探头,对2006年夏季广东省从化地区发生的自然闪电的光电信号进行了同步观测,并对结果进行了统计分析。统计结果表明：闪电光信号脉冲的发生时间和峰值到达时间总是滞后于电信号,并且脉冲上升沿和宽度也比电信号宽;云闪的光信号在上述特征参数的滞后量、上升沿时间和脉宽时间差要比地闪回击放电大。从闪电光电信号时域信号特征的角度,利用BP人工神经网络,对闪电类型进行了模式识别研究。总体识别结果基本上能够满足要求,但是由于云闪放电过程比较复杂,获得的数据较少,所以对云闪识别的效果并不理想。     

闪电光电信号的同步观测与闪电类型模式识别

利用宽带电场仪和光学纹波探头,对2006年夏季广东省从化地区发生的自然闪电的光电信号进行了同步观测,并对结果进行了统计分析。统计结果表明：闪电光信号脉冲的发生时间和峰值到达时间总是滞后于电信号,并且脉冲上升沿和宽度也比电信号宽;云闪的光信号在上述特征参数的滞后量、上升沿时间和脉宽时间差要比地闪回击放电大。从闪电光电信号时域信号特征的角度,利用BP人工神经网络,对闪电类型进行了模式识别研究。总体识别结果基本上能够满足要求,但是由于云闪放电过程比较复杂,获得的数据较少,所以对云闪识别的效果并不理想。     

Electrical and radiative processes in ball lightning

Summary The observational parameters of ball lightning are given, together with an analysis of electrical processes during the origin and evolution of ball lightning. It is suggested that ball lightning formation takes place in a unipolar plasma with a high concentration of charged particles. According to the analysis such a plasma is formed as a results of electric breakdown of atmospheric air between a dust cloud and a hard surface. A comparison is made between observational ball lightning as a light source, a black body and a flame. It is shown that the luminosity of ball lightning is created by separated hot regions with a temperature of about 2000 K. Excited atoms or molecules in these regions are found in thermodynamical equilibrium with air. The waves of ball lightning luminosity spread along separated threads of the active substance of ball lightning, with some 10²⋎10⁴ threads being involved in this process. The luminisity of many points is perceived as a volume radiation of ball lightning.

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Riassunto Si danno i parametri d’osservazione del ball lightning insieme ad un’analisi di processi elettrici durante la sua origine e evoluzione. Si suggerisce che la sua formazione avvenga in un plasma unipolare con alta concentrazione di particelle cariche. Secondo l’analisi tale plasma si forma in quanto risultato di una scarica disruttiva di aria atmosferica tra una nuvola di polvere e una superficie dura. Si fa un confronto tra il ball lightning osservato come fonte di luce, un corpo nero e una fiamma. Si mostra che la luminosità del ball lightning si crea da regioni calde separate con una temperatura di circa 2000 K. Si trova che atomi eccitati o molecole in queste regioni sono in equilibrio termodinamico con l’aria. Le onde di luminosità del ball lightning si diffondono lungo fili separati della sostanza attiva del ball lightning con circa (10²⋎10⁴) fili coinvolti in tale processo. La luminosità di molti punti è percepita come radiazione di volume del ball lightning.

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Резюме Приводятся наблюдаемые параметры шаровой молнии. Анализируются электрические процессы при образовании и эволюции шаровой молнии. Предполагается, что шаровая молния образуется в униполярной плазме с высокой концентрадией заряженных частиц. Согласно проведенному анализу, такая плазма образуется в резяльтате электрического пробоя атмосферного воздуха между рылевым облаком и твердой поверхностью. Проводится сравнение наблюдаемой шаровой молнии, как источника света, света, с черным телом и с пламенем. Показывается, что излучение шаровой молнии обрззуется отдельными горячими областями с температурой около 2000 К. Отмечается, что возбужденые атомы или молекулы в этих областях находятся в термодинамическом равновесии с воздухом. Волны илучения шаровой молнии распространяются вдоль отдельных нитей активного вещества шаровой молнии, причем в процессе участвует порядка 10²⋎10⁴ нитей. Светимость большого числа точек воспринимается как объем излучения шаровой молнии.

     

The striking distance of lightning flashes and the early streamer emission (ESE) hypothesis

The attachment of a lightning flash to a lightning conductor (or to any other structure) takes place through a connecting leader that rises from the structure towards the descending stepped leader of a lightning flash. The spatial separation between the tip of the stepped leader and the lightning conductor (or the grounded structure) at the initiation of the connecting leader is known as the striking distance. In this paper the striking distance of stepped leaders is derived as a function of conductor height, conductor radii and the prospective return stroke current. Based on these results the validity of the early streamer emission (ESE) hypothesis is discussed. According to the ESE hypothesis, the striking distance of a lightning conductor can be increased by the artificial initiation of streamers from a lightning conductor. The results cast doubt on the validity of the ESE hypothesis. This in turn calls for more experimental data and field validations before using the ESE hypothesis in standard lightning protection practice.     

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.     

On the possibility of phosphenes being generated by the energetic radiation from lightning flashes and thunderstorms

After the first report of this phenomenon by Apollo 11 astronauts, experiments conducted in space and on the ground confirmed the creation of phosphenes by the interaction of energetic radiation with the human visual system. The aim of this Letter is to show that the energetic radiation generated in the form of X-rays, gamma rays, electrons and neutrons by thunderstorms and lightning is strong enough for the creation of phosphenes in humans. It is also pointed out that some of the visual observations reported during thunderstorms might be attributable to phosphenes excited by this energetic radiation.     

Neutron bursts during cloud-to-ground discharges of lightning

Neutron bursts of up to 30% per minute resolution are recorded by the Yakutsk cosmic ray spectrograph during jumps of an electric field undergoing changes in the vicinity of the neutron monitor upon cloud-to-ground discharges of lightning. The electric field variations are recorded with an electrostatic fluxmeter (±50 keV m^?1).     

On the attachment of lightning flashes to grounded structures with special attention to the comparison of SLIM with CVM and EGM

Lightning attachment to vertical grounded conductors are presented with special attention to the lightning attractive radii of vertical conductors as predicted by self consistent leader inception and propagation model (SLIM), Electro Geometrical Model (EGM) and Collection Volume Method (CVM). Moreover, SLIM was utilized to model the attachment of a slanted stepped leader to a tall tower that resulted in a side flash to a point below the top of the tower. The important conclusions to be drawn from the results obtained are the following: (a) The error (caused by neglect of the connecting leader in EGM) in the predicted attractive radii and the striking distance of EGM increases with increasing structure height. However, for structures whose height is shorter than about 30 m the error associated with using EGM is less than about 20%. (b) The attractive radii predicted by the Collection Volume Method (CVM) are much larger than the ones predicted by SLIM and EGM. Thus, the use of CVM to locate the lightning conductors on a structure may undermine its safety. (c) Slanted stepped leader channels can cause side flashes in tall structures even though long connecting leaders are emitted from the top of the structure.     

Numerical simulations of thunderstorm-induced corona processes near lightning rods installed on grounded structures

For the purpose of estimating the efficacy of a lightning rod, the current of a corona was numerically calculated from a rod placed (i) centrally on the roof of a vertical grounded cylindrical structure, a model of a man-made object, and (ii) at the top of a grounded hemispherical structure of large radius, such as a hill or mountain. The calculations were carried out for a slowly varying thundercloud electric field and when this field was enhanced by the charge of an approaching downward leader. In case (i), variation of the ratio between the height and radius of the cylindrical structure leads to a variation in the (a) corona current from the tip of the rod over a wide range and (b) distance from which lightning is attached to the rod. In case (ii), it is shown that, contrary to the case of rods installed on the ground surface, a slowly rising thundercloud electric field can be sufficient to initiate streamers and upward leaders from rods tens of meters in height installed on the top of tall, grounded, hemispherical structures. When the thundercloud electric field is enhanced by the charge of an approaching downward leader, the discharge processes near the rod depend on its length and the height of the tip of the downward leader relative to the top of the hemispherical structure, but are almost independent of the hemisphere radius.     

Modeling the development of the stepped leader of a lightning discharge

A stochastic-deterministic model is presented for the propagation of a downward-moving leader. Lightning formation is described by a stochastic growth of branching discharge channels which is determined by the electrostatic field. The dynamics of the electric field and of the charge distribution over the lightning structure are calculated deterministically. The model includes the initiation of lightning, a preliminary discharge in a cloud, the propagation of a downwardmoving stepped leader toward the earth, and the initiation and upward motion of a return stroke from the earth’s surface. Numerical execution of the model yields a dynamic picture of the development of the downward-moving leader and of the intracloud discharge structure. The effect of the charge density in the cloud and the parameters of the developing channels on the spatial-temporal, current, and charge characteristics of the stepped leader’s propagation are studied. The effect of free-standing structures on the distribution of points on the earth’s surface where lightning strikes is examined. Zh. Tekh. Fiz. 69, 48–53 (April 1999)     

Physical processes in breakdown of silicon monoxide film

At present the mechanics of breakdown of dielectric films is a topic of active discussion.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 36–41, November, 1972.In conclusion the authors express gratitude to N. S. iVIukhacheva for help in conducting the experiment.     

Twinning processes during chemoepitaxy

We present the results of studies on twinning processes in the reactive diffusion zone when copper, antimony, and chromium crystals are saturated with elements from outside. An explanation is provided for the intense rate of twinning processes on the basis of the anomalies of the chemoepitaxial growth of the material.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 58–61, March, 1987.