Lightning is important for all scientists and engineers involved with electric installations. It is gaining further relevance since climate warming is causing an increase in lightning strikes, and since the rising numbers of renewable power generators, the electricity grid, and charging infrastructure are susceptible to lightning damage. This is the second edition to this comprehensive work.
Both volumes have been thoroughly revised and updated for this second edition. Volume 1 treats lightning return stroke modelling and lightning electromagnetic radiation, and Volume 2 addresses electrical processes and effects. Chapter coverage includes various models and simulations of lightning strokes, measurements of lightning-generated EM fields, HF, VHF and microwave radiation, and lightning location systems; atmospheric discharge processes, lightning strikes to grounded structures and towers, EM field propagation, interaction with cables, effects on power transmission and distribution systems, effects in the ionosphere, mesosphere and magnetosphere, as well as NO x generation and climate effects. The volumes provide the rules and procedures to combine the readers' understanding with a model of every lightning-related electromagnetic process, and their effects and interactions. Readers obtain first-hand experience through simulations of the EM field of thunderclouds and lightning flashes and their effects.
These volumes are a valuable resource for researchers and engineers in the areas of electrical engineering and physics involved in the fields of electromagnetic compatibility, lightning protection, renewable energy systems, smart grids, and lightning physics, as well as for professionals from telecommunication companies and manufacturers of power equipment, and advanced students.
Inspec keywords: lightning; lightning protection; troposphere; electron density; thunderstorms; air pollution; clouds
Other keywords: air pollution; thunderstorms; troposphere; electrical processes; discharges (electric); corona; lightning protection; electron density; electromagnetic fields; clouds
Subjects: Atmospheric storms; Cloud physics; Power system protection; Atmosphere (environmental science); Atmospheric electricity; Air quality and air pollution; Textbooks
The main constituents of air in the Earth's atmosphere are nitrogen (78%), oxygen (20%), noble gases (1%), water vapour (0.03%), carbon dioxide (0.97%), and other trace gas species. In general, air is a good insulator and it can maintain its insulating properties until the applied electric field exceeds about 2.8 × 104 V/cm at standard atmospheric conditions (i.e. T = 293 K and P = 1 atm). When the background electric field exceeds this critical value, the free electrons in air, generated mainly by the high energetic radiation of cosmic rays and radio active gases generated from the Earth, start accelerating in this electric field and gain enough energy between collisions with atoms and molecules to ionize other atoms. This cumulative ionization leads to an increase in the number of electrons initiating the electrical breakdown of air. The threshold electric field necessary for electrical breakdown of air is a function of atmospheric density.
Our goal in this chapter is to introduce the treatments of electrical processes used by numerical cloud models that integrate dynamic, microphysical, thermodynamic and electric processes to track what happens to several classes of water particles as they move through the cloud and interact with each other and with the environment as the cloud evolves. We consider primarily models that treat ice particles, as well as liquid water, because ice is now commonly recognized as a necessary ingredient for strong electrification. We ignore models whose winds or particle spectra are unchanging and models that treat electrification as interactions of electric circuit elements driven by a current, charge or voltage source unrelated to microphysics and dynamics.
Electrical gas discharges belong to the class of low-temperature plasmas. Depending on particular conditions, they can be equilibrium (thermal) or non-equilibrium (non-thermal) meaning that temperatures/energies of constituting particles (electrons, ions, neutral atoms/molecules) are either nearly equal or different, respectively. Examples of the former are electric arcs, sparks, microwave discharges, where such effects like Joule heating of the gas and its thermal ionization are significant. In contrast, non-thermal discharge plasmas are characterized by presence of highly energetic electrons in "cold" neutral gas and ionic component with temperature close (or slightly higher) to that of gas. Typical examples of these are electron avalanches, glow discharges, streamers, electrical coronas, where the degree of ionization of the gas is much less than unity, the electron density rarely exceeds ~1014 cm-3 and their mean energy is normally below ~10 eV.
This chapter deals with basic principles of numerical simulations of non-thermal electrical discharges in air, which are predecessors and indispensable attributes of a leader discharge (see, e.g., [1]). First, processes in such discharges and a theoretical background of so-called fluid model are considered. Further, numerical approaches utilized for computer implementation of the model are presented. Finally, examples are given including computer simulations of coronas as well as positive and negative streamers.
The main conclusion that can be extracted from the work presented in the chapter is that the connecting leader does not play a significant role in the case of lightning attachment to normal (i.e. short) structures. For structures shorter than about 30 m, one can use EGM without significant errors. However, it is important to stress here that this difference may still play an important role when two conductors are competing with each other to get attached to a down-coming stepped leader. In such cases, the predictions of EGM and SLIM so as to the point of attachment may differ from each other.
Note also that in the comparison between lightning strike models, the same leader charge distribution and leader potential should be used in all models. It is only then the concepts and predictions of different models could be tested against each other. This is a point worth keeping in mind because there are many lightning strike models in the literature, each based on a different leader charge distribution or leader potential.
In this chapter, we present a review of recent progress in the modeling of lightning strikes to tall structures. Since some tall structures are struck by lightning several tens of times per year, they can be used as ground-truth to measure and calibrate the location accuracy of lightning location systems. In addition, knowledge of the transient processes in tall objects when they a subjected to a lightning strike allows us to use them to calibrate the lightning return stroke currents reported by lightning detection and location systems. Tall objects constitute also a primary source of data from which channel-base lightning current statistics are obtained. These statistics are in turn used to improve the design of lightning protection devices and systems.
This chapter is organized as follows: Section 5.2 presents a review of the extension of lightning return stroke models to include the presence of an elevated strike object. Section 5.3 deals with the computational methods for the evaluation of the electromagnetic fields generated by lightning strikes to tall structures. A review of available data on lightning currents from lightning to tall structures is presented in Section 5.4. Finally, a summary is given in Section 5.5.
During the past decades, much attention has been paid to the problem of the interaction between lightning electromagnetic fields and overhead and buried conductors. This has led to the formulation of different reliable field-to-transmission line coupling models [1,2]. All these models require an accurate evaluation of the lightning electromagnetic fields along the line, taking into account the effect of the ground finite conductivity, since the approximation of perfectly conducting ground becomes unacceptable especially in the evaluation of the horizontal electric field [3].
Different models can be adopted to represent a lossy soil; the simplest one assumes that both the conductivity σ and the relative permittivity εr are constant. Enhanced representations could then consider the influence of the working frequency on σ and εr or their dependence on the depth, in the case of a horizontally stratified ground. In the following, such configurations will be examined with the final aim to derive lightning field expressions (radial and vertical electric field, azimuthal magnetic one) and to propose numerical procedures for their efficient and accurate calculation. It is important to highlight from the beginning that the presence of a ground with finite conductivity will be responsible of the appearance in field expressions of the so-called Sommerfeld's integrals. The numerical evaluation of such integrals represent a hard task due to the singular, oscillating and divergent behaviour of their integrands and, as a consequence, suitable strategies have to be identified to guarantee at the same time precision in execution and acceptable computational costs.
The chapter is organized as follows. In Section 6.2, the ground parameters will be considered constant; under such assumption both the derivation and the calculation of the lightning electromagnetic field components will be presented.
Next, in Section 6.3, the influence of the frequency dependent behaviour of the ground electrical parameters will be studied. Finally, in Section 6.4, the problem of the derivation of the lightning electromagnetic fields over a stratified conducting ground will be faced.
In this chapter, a review of the main approximate expressions available in literature to evaluate lightning electromagnetic fields that propagate over and under a lossy ground is presented together with their validation against exact expressions or full Maxwell approaches.
First the case of homogeneous ground is analyzed presenting the two main approximate expressions for the horizontal electric field above the ground (Cooray Rubinstein formula, Section 7.1) and below the ground (Cooray's formula, Section 7.2).
Then, the most popular expressions for electromagnetic fields propagating over a horizontally (Section 7.3) and vertically (Section 7.4) stratified ground are reported and validated.
In this chapter, we discussed the TL theory and its application to the problem of lightning electromagnetic field coupling to transmission lines.
After a short discussion on the underlying assumptions of the TL theory, we described seemingly different but completely equivalent approaches that have been proposed to describe the coupling of electromagnetic fields to transmission lines.
The field-to-transmission line coupling equations were then extended to deal with the presence of losses and multiple conductors and expressions for the line parameters, including the ground impedance and admittance were presented. The time-domain representation of the field-to-transmission line coupling equations, which allows for a straightforward treatment of nonlinear phenomena as well as the variation in the line topology, was also described. Solution methods in the frequency domain and in the time domain were given and application examples with reference to lightning-induced voltages were presented and discussed.
Specifically, the effect of ground losses was illustrated and discussed. When the travelling voltage and current waves are originated from lumped excitation sources located at a specific location along a transmission line (direct lightning strike), both the corona phenomenon and ground losses result in an attenuation and dispersion of propagating surges along transmission lines. However, when distributed sources representing the action of the electromagnetic field from a nearby lightning illuminating the line are present, ground losses and the corona phenomenon could result in important enhancement of the induced voltage magnitude.
Finally, we reviewed the theory of electromagnetic field coupling to a buried cable. Solution methods in the frequency and the time domain were also presented. Examples of lightning-induced currents and comparison with experimental data were presented.
The scale model technique is a very powerful and versatile tool for the analysis of the interaction of lightning with electric power lines, and well complements other methods such as rocket-triggered lightning and experiments with full-scale systems. It enables the simulation of a wide variety of situations and, moreover, tests can be carried out under controlled conditions. After the system implementation, a substantial amount of data can be obtained in a relatively short time.
An important application of scale models concerns the validation of theoretical models of complex phenomena and their relevant codes. They can also be very useful in the evaluation of the influence of the line configuration and of various lightning parameters on the overvoltages' magnitudes and waveforms, which can be assessed with satisfactory accuracy. In this chapter, the usefulness of the method was illustrated by its application for the validation of the ERM and LIOV-EMTP predictions, as well as for the investigation of the behavior of lightning transients on overhead power transmission and distribution lines subjected to direct and indirect strokes. The technique is particularly suitable for the analysis of situations that are either too complex or not worthwhile to be treated theoretically, as e.g. the case of lightning-induced voltages on urban power distribution networks surrounded by nearby buildings.
Lightning discharges, including cloud-to-ground (CG) and intracloud (IC) lightning, are known to emit electromagnetic pulses (EMPs) in a wide frequency band ranging from few Hz up to hundreds MHz [1]. During the breakdown and ionization processes (mostly from leader processes and streamers), there are strong emissions in the HF (3-30 MHz) and VHF (30-300 MHz) bands. When high currents occur in previously ionized channels (mostly from return strokes and the active stage of cloud flashes), the most powerful emissions concentrate in the very low frequency (3-30 kHz, VLF) and low frequency (30-300 kHz, LF) bands [2]. Among them, the VLF/LF waves of lightning discharges can propagate long distances with low attenuation by reflection between the ground surface and the lower D-region ionosphere (60-90 km), namely the so-called earth-ionosphere waveguide (EIWG).
In order to investigate the lightning EMPs interaction with the ionosphere, a number of models and methods have been developed in the literature, such as the wave-hop (ray theory) method [3-6], the waveguide mode theory [7-9], or numerical methods such as the finite-difference-time-domain (FDTD) method [10-17] and the full-wave finite element method (FEM) [18,19]. Previous studies indicate that the amplitude and phase perturbation for lightning VLF/LF signals have a complicated relationship with the ionospheric D region parameters. The propagation of lightning EMPs between the earth ground surface and the lower D region ionosphere can be affected by many factors, such as the propagation distances [10,14,20], the ground conductivity [14,20], the electron and neutral particle densities [13,21,22], the Earth curvature [23,24], the presence of the Earth's magnetic field [22,25-27], and the presence of mountainous terrain [24].
In this chapter, we will first introduce the propagation theory of lightning EMPs interaction with the ionosphere on the basis of the full-wave FDTD method. We will then investigate the propagation effect of lightning radiated electromagnetic (EM) fields in the EIWG by considering the effect of the Earth curvature, the effect of the ground conductivity, and the effect of different ionospheric profiles. Finally, we will present applications, including (1) propagation of narrow bipolar events (NBEs) at different distances, (2) lightning electromagnetic fields propagation over mountainous terrain, and (3) the optical emissions of lightning-induced transient luminous events in the nonlinear D-region ionosphere.
Spectacular large-scale optical flashes in the stratosphere and mesosphere above large thunderstorm systems were first discovered by Franz et al. [1] serendipitously during a test of a low-light television camera. Interestingly, this phenomenon was predicted by the Nobel prize winner C.T.R. Wilson back in the 1920s [2]. And since then, there has been a lot of evidence from airplane pilots and other eyewitnesses about short-term light flashes of various shapes and colors over storm clouds [3].
One of the main reasons why this phenomenon was discovered so late is the difficulty of observing this phenomenon from the earth's surface since the optical flashes in the stratosphere and mesosphere are closed to the observer by thunderclouds. In ground-based measurements, the giant optical flashes above thunderclouds can be seen at a small angle to the horizon at distances of hundreds of kilometers from the flash site. In addition, they have a very short duration and occur much less common than ordinary cloud-to-ground lightning (e.g., [4], and references therein).
This chapter will present possible effects of atmospheric lightning on the upper atmosphere such as the ionosphere and magnetosphere composed of ionized plasmas. Though there exist several phenomena on the effect of lightning discharges onto the ionosphere/magnetosphere, we introduce only two major attractive topics: (1) lightning-induced whistlers in the ionosphere/magnetosphere, and (2) ionospheric Alfvén resonator (IAR) in an altitude region between the lowest ionosphere and lower magnetosphere, where one likely candidate of its source is lightning discharges. The former is quite a well-known phenomenon, and whistlers are bursts of ELF/VLF waves produced by lightning discharges. Some part of VLF/ELF lightning energy penetrates through the ionosphere, propagates along the magnetic field line in the magnetosphere, and penetrates again through the ionosphere in the opposite hemisphere, followed by reception on the ground as a whistler. We show initially the phenomena of ground-based whistlers, their brief theoretical explanation, and their use in the diagnostics of ionospheric/magnetospheric electron density. Also, earlier satellite observations of nonducted whistlers are presented. Further, we will describe recent satellite observations of short-fractional hop whistlers and VLF/ELF electromagnetic waves, with special reference to their use in the study of global lightning activity. On the other hand, the latter phenomenon, IAR in the ULF/ELF band is a rather new subject as compared with whistler studies, and so we pay more emphasis on IAR in this chapter. IARs exhibit an interesting feature of fingerprint resonance structures on the dynamic spectra. This IAR is apparently considered to be a kind of resonance of Alfvén waves in a region between the lowest ionosphere and lower magnetosphere, whose resonance frequencies (f = 1-10 Hz) are lower than the well-known Schumann resonances. We present our own statistical results on morphological characteristics of IARs (spectral resonance structures) at middle latitudes as your basis to understand the resonance structure of IARs. Then we will review the physical mechanisms, in other words, the energy source of IAR signatures seems to depend on latitude. Though there are considerable uncertainties in the physical modeling, we will suggest a plausible hypothesis as the origin of IARs at middle and low latitudes; the link to nearby lightning discharges. Lastly, a summary will follow.
An assessment of the global distribution of nitrogen oxides (NO x ) is required for a satisfactory description of tropospheric chemistry and in the evaluation of the global impact of increasing anthropogenic emissions of NO x [1]. In the mathematical models utilized for this purpose, it is necessary to have the natural as well as man-made sources of NO x in the atmosphere as inputs. Thunderstorms are a main natural source of NO x in the atmosphere and it may be the dominant source of NO x in the troposphere in equatorial and tropical South Pacific [2].
Footnote: This material was published previously by the same authors in Open Atmospheric Science Journal, vol. 2, pp. 176-180, 2008. It is reproduced here by permission from the journal.
An assessment of the global distribution of nitrogen oxides is required for an adequate description of tropospheric chemistry and in the evaluation of the global impact of increasing anthropogenic emissions of NO x [1]. In the mathematical models utilized for this purpose, one needs to specify as inputs the natural as well as man-made sources of nitrogen oxides in the atmosphere. Lightning is one of the main natural sources of nitrogen oxides in the atmosphere, and it may be the dominant source of nitrogen oxides in the troposphere in equatorial and tropical South Pacific regions [2]. Thus, an accurate quantification of nitrogen oxide production by thunderstorms is necessary for further development of the chemical models of the troposphere and in the evaluation of the effects of the man-made nitrogen emissions in the terrestrial atmosphere.
Footnote: This material was published previously by the same authors in Journal of Atmospheric and Solar-Terrestrial Physics, vol. 71, pp. 1877-1889, 2009. It is reproduced here by permission from the journal.
Lightning is a widely recognized source of damage and disruption to electrical power systems worldwide. The climate is changing, with both natural and anthropogenic origins. This chapter is concerned with the response of lightning to changes in temperature and aerosol loading of the atmosphere that is expected to accompany climate change. In the present climate, lightning is shown to increase with both temperature and with the boundary layer populations of cloud condensation nuclei (CCN). In a future climate characterized by the continued consumption of fossil fuels, the threat from lightning is expected to increase.