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Initial global extremes in lightning duration and horizontal distance were established in 2017 (Lang et al. 2017) by an international panel of atmospheric lightning scientists and engineers assembled by the WMO. The subsequent launch of NOAA’s latest GOES-16/17 satellites with their Geostationary Lightning Mappers (GLMs) enabled extreme lightning to be monitored continuously over the western hemisphere up to 55° latitude for the first time. As a result, the former lightning extremes were more than doubled in 2019 to 709 km for distance and 16.730 s for duration (Peterson et al. 2020). Continued detection and analysis of lightning “megaflashes” (Sequin, 2021) has now revealed two flashes that even exceed those 2019 records. As part of the ongoing work of the WMO in detection and documentation of global weather extremes (e.g., El Fadli et al. 2013; Merlone et al. 2010), an international WMO evaluation committee was created to critically adjudicate these two GLM megaflash cases as new records for extreme lightning. We thank S. A. Rutledge and two other reviewers for their valuable comments. M. J. Peterson was supported by the U.S. Department of Energy through the Los Alamos National Laboratory (LANL) Laboratory Directed Research and Development (LDRD) program under project number 20200529ECR. Los Alamos National Laboratory is operated by Triad National Security, LLC, for the National Nuclear Security Administration of U.S. Department of Energy (Contract 89233218CNA000001). T. Logan supported by a NOAA Grant NA16OAR4320115 “Lightning Mapper Array Operation in Oklahoma and the Texas Gulf Coast Region to Aid Preparation for the GOES-R GLM.” I. Kolmasova was supported by GACR Grant 20-09671. S. D. Zhang was supported by a NOAA Grant NNH19ZDA001N-ESROGSS. The participation of J. Montanya in this work is supported by research Grant ESP2017-86263-C4-2-R funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe,” by the “European Union”; and Grants PID2019-109269RB-C42 funded by MCIN/AEI/10.13039/501100011033.

We present the first high spectral resolution (0.24 nm) spectra of sprites. These spectra were recorded in Europe in the summers and falls of 2015 and 2016 and during January 2017. The use of high spectral resolution has allowed us to resolve for the first time the internal (vibrorotational) structure of the sprite molecular N2 first positive system and to quantify the local gas (rotational) temperature of the mesosphere under the influence of sprites revealing that there is no measurable heating of the atmosphere associated to sprites at the altitudes explored. The temperatures of the explored region of the mesosphere range between 149 K ± 10 K and 226 K ± 20 K. The recorded spectroscopic data also provide valuable quantitative information on the concentrations of some of the vibrational levels of molecular nitrogen involved in transient red-near-infrared optical emissions from sprites. The regions of the transient luminous events recorded with our spectrograph (equipped with a horizontally oriented slit) correspond to altitudes in the 66 km to 74 km ± 5 km range. ©2018. American Geophysical Union. All Rights Reserved., This work was supported by the Spanish Ministry of Science and Innovation, MINECO, under projects FIS2014-61774-EXP, ESP2015-69909-C5-2-R, and ESP2017-86263-C4-4-R, and by the EU through the FEDER program. The contribution of O. V. and J. M. was supported by projects ESP2013-48032-C5-3-R and ESP2015-69909-C5-5-R. A. L. was supported by the European Research Council (ERC) under the European Union H2020 program/ERC grant agreement 681257. We acknowledge NowCast for providing LINET lightning data for research purposes. We also acknowledge AEMET (Spanish Meteorological Service) for providing some lightning data corresponding to January 2017.

It is well known that tall structures such as telecommunication towers can be exposed to numerous lightning incidence. Wind turbines are in this group, but two particular characteristics distinguish wind turbines from the rest. The first peculiarity is that a substantial part of the structure is rotating. That corresponds to the rotor blades. The second, is also related to the rotor blades and corresponds to the intensive use of composite materials. Due to these two factors, protection against lightning requests very special attention.

During the night of October 29-30, 2013, a low-light video camera at Pic du Midi (2877 m) in the French Pyrénées, recorded TLEs above a very active storm over the Mediterranean Sea. The minimum cloud top temperature reached -73 °C at ~1600 UTC while its cloud to ground (CG) flash rate reached ~30 fl min-1. Some sprite events with long duration are classified as dancing sprites. We analyze in detail the temporal evolution and estimated location of sprite elements for two cases of these events. They consist in series of sprite sequences with a duration that exceeds 1 second. By associating the cloud structure, the lightning activity, the electric field radiated in a broad range of low frequencies and the current moment waveform of the lightning strokes, some findings are highlighted: (i) In each series, successive sprite sequences reflect the occurrence time and location of individual positive lightning strokes across the stratiform region. (ii) The longer time-delayed (> 20 ms) sprite elements correspond to the lower impulsive charge moment changes (iCMC) of the parent stroke (< 200 C km) and they are shifted few tens of kilometres from their SP+CG stroke. However, both short and long time-delayed sprite elements also occur after strokes that produce a large iCMC and that are followed by a continuing current. (iii) The long time-delayed sprite elements produced during the continuing current correspond to surges in the current moment waveform. They occur sometimes at an altitude apparently lower than the previous short time-delayed sprite elements, possibly because of the lowered altitude of the ionosphere potential. (iv) The largest and brightest sprite elements produce significant current signatures, visible when their delay is not too short (~3-5 ms).

Electromagnetic field from simulated double-headed mid-gap streamers is computed. The effect of the applied electric field is studied by considering electric fields higher than the conventional breakdown threshold (‘overvoltage’). The obtained results show a 20 dB decay at 3.8 GHz for conventional breakdown electric field, 35 GHz for ambient electric fields five times the conventional breakdown and 170 GHz for fields ten times the conventional breakdown electric field. The limitation in nature of the intense electric fields suggest further experiments using a radio receiver at frequencies of more than 10 GHz in order to investigate the origin of the detected x-rays in laboratory sparks.

Multi-megawatt wind turbines are a special type of tall structures. Two characteristics stand out from other tall objects such as buildings and telecommunication towers. The first particularity is that a large part of the structure is rotating, and the second, is the extensive use of composite materials in the rotor blades. Due to these two factors, the protection against lightning requests very special attention. Wind turbines installed all over the world have shown how a particular design of their lightning protection system (LPS) can perform very different in areas with different thunderstorm climatology. Up to now, the most severe damages are reported in those areas affected by winter thunderstorms such as Japan and Europe (e.g. Honjo, 2015). These type of storms pose the most favorable conditions for upward lightning initiation from tall structures. That is because the heights of charge regions of winter thunderstorms are significantly low (e.g. Montanyà et al., 2007). On the other hand, most wind turbine blades are built wind composite materials such as glass fibers (GF) and carbon reinforced plastics (CFRP). Blades are typically composed of two shells enclosing a spar. The lighting protection system consists of one or several air terminals connected to a down conductor that brings lightning currents to ground (e.g. IEC 61400-24, 2010). However, the insulation provided by the shells is not perfect and it is possible to experience lightning attachments to non-desired locations. Some blades are equipped with electrically conductive carbon fiber reinforced plastics (CFRP), these components shall be bonded to the lightning protection system (IEC 61400-24, 2010). CFRP laminates are poor conductive presenting high anisotropy. Moreover, electrical connections to CFRP can be very complex because in most of the cases it is not possible to use bolted connections. In the first part of this work lightning interactions to wind turbines are described according to the types of thunderstorms. The effects of the different type of interactions to the calculation of risk assessment is discussed. In the second part, lightning damages are treated. This include a review of the mechanisms of damages and statistics. The case of incidences to blades and protection to CFRP components are highlighted.

Carbon Fiber Reinforced Plastic (CFRP) components are commonly present in new generation of wind turbine blades and aircraft. CFRP components are preferred for its good mechanical strength and low weight. However, CFRP is more vulnerable to lightning currents and arcs. In addition, CFRP can present very anisotropic electric properties that can difficult its lightning protection. In this paper we present two types of tests intended for improving the understanding of electrical properties of CFRP useful for lightning protection. The experimental and simulation study of the potential distribution along a CFRP coupon suggest how the currents are distributed and some defects in the electrical connections. A new method in order to investigate connection effectiveness in full scale wind turbine blades is proposed. The method is minimal invasive. The second part of the paper discusses the possible current paths in different arrangements of connections by means of thermal imaging

This paper presents thunderstorm electrostatic field measurements carried out by electric field mills located at mountainous regions in Spain and Colombia. The profile of electric field changes ¿E due to lightning vs distance is computed by using data from a lightning location system. The effect of the topography on the ¿E vs distance profile is studied in order to identify necessary adjustments for field mills used as lightning warning systems affects by topographycal factors.

Lightning involves high energy processes that still are not well understood. In the laboratory voltages pulses are used to produce long sparks allowing the production of energetic radiation. In this paper X-rays emitted by long sparks in air are simultaneously measured with the RF power radiation at ¿2.4 GHz. The experiment showed that RF power systematically peaks at the time of the X-rays generation (in the measurement time scale). Sparks presents peaks of RF radiation before the breakdown of the gap. The peaks are related to the applied voltage to the gap. RF peaks are also detected in discharges without breakdown. Cases where X-rays are detected present higher RF peak power. The results indicate that at some stage of the discharge before the breakdown electrons are very fast accelerating letting in some cases to produce X-rays. Microwave radiation and X-rays may come from the same process.

RHESSI and AGILE TGFs distributions in the period 2009-2012 are compared. Analysis of differences in geographical, hourly, monthly distributions of the three main TGF production regions in Earth due to differences in lightning production and ITCZ movement is presented. A fourth region producing TGFs over Pacific not reported before is also analysed. Second analysis has been performed in order to identify preferable meteorological conditions for TGF production. Some publications suggested that regional differences in lightning/TGF ratio may be due to differences in meteorological thunderstorm and lightning production. All AGILE passes over South America (SA) in 2009-2012 has been studied. No special meteorological features characteristic of SA has been identified. TGFs are detected in situations with many lightning, thunderstorms, high CAPEs and high Top Clouds. TGFs are more probable to be detected in active situations.

El delta de l’Ebre presenta les característiques idònies per ser un gran laboratori a l’aire lliure per a l’observació de llamps i d’altres fenòmens elèctrics, que tenen lloc per sobre dels núvols de tempesta. Aquests cosins dels llamps, de formes sorprenents, no es van descobrir fins a finals dels 90 i han despertat un gran interès en la comunitat científica.

Sprites and Elves are commonly observed in Europe, especially also in winter maritime storms. It is well known that sprites are related to large electric charge positive flashes and elves are related with high amplitude in either negative and positive flashes. The analysis of the occurrence of sprites and elves revealed that sprites can occur inland and over the sea whereas elves prefer to occur over the sea. The distribution of positive and negative flashes during the warm period (April-September) and the cold period (October-March) depicts that flashes with intense amplitudes present a particular pattern. Intense negative flashes occur mostly over the sea and coastal areas during summer and winter whereas intense positive tend to occur in the mountains during the warm season and over sea during the cold period. Also, sprite and elves can indicate regions where energetic flashes occur. This can be a valuable information related to the risk assesment of wind turbines.

X-ray produced by laboratory sparks in air at atmospheric pressure for rod-rod and rod-plane configurations were observed. A total of 585 sparks were applied with both polarities. The paper shows the effects of the voltage rise time and the peak voltage in the generation of x-rays. It is found here that shorter rise times and high peak voltages tend to produce more x-rays emissions with higher energies than longer front waveforms or lower peak voltages. In a similar way, higher voltage variations produce more energetic emissions. This finding suggests that the variation of the electric field before the breakdown can play a fundamental role in the x-ray production. The results are similar with the observations of x-rays produced in natural lightning where detections have been associated to leader steps before the return stroke.

A new subject on lightning protection of aircraft has been developed at the Technical University of Catalonia. This elective subject is implemented according to project-based learning (PBL). In this way, during the subject, students face up to a design and validation of a lightning protection system of an aircraft.

This paper presents simulations of a downward negative leaders performed by means of 3D finite element method (FEM). The leaders are considered do progress vertically leaders in which different charge distributions and leader speeds can be adjusted. The output of the model is the electric field at ground level for different leader heights and time. By comparison with experimental measurements of natural cloud-to-ground stepped leaders we find consistent results by adjusting the speed of the leader.

Lightning detections of the Catalan Lightning Location Network (XDDE) are compared with high speed video recordings carried out in Spain during summer 2009. At that time the XDDE was composed by four sensors: two SAFIR 3000 type and two LS8000 type. The comparison showed good agreement in the observations at the center and at the south of the network. However, the observations recorded at the north of the network showed a poorer detection efficiency and location accuracy. On the other hand, the fine comparison between frame by frame of video recordings and network detections reveals that the network often detects mostly intra-cloud (IC) sources which probably belong to the preliminary breakdown in downward cloud-to-ground flashes. In some cases few sources are detected during steeped leaders toward to the ground. In the case of our observed IC flashes, the detected sources never corresponded to observations of propagation leaders, if not, small burst of detections were linked to permanent illuminated channels or permanent visible luminosity from the cloud.

Wind turbine blades are the most exposed parts of the turbine, and would experience the full impact from the electric fields as associated with the lightning attachment process, the lightning currents, and the magnetic field associated with lightning currents.At some point in time hopes were high that lightning would not strike blades made of non-conducting material only, but practical experiences have clearly demonstrated that this is not the case. Lightning does in fact strike blades without any metallic components, and whenever a lightning arc is formed inside the blade damage is severe.

This study presents an analysis of total lightning and radar data of a severe weather event that took place in the early morning of 2nd November 2008 in Catalonia (NE Spain). A general overview of the synoptic framework and damage observed, including local flash floods, strong wind gusts and an F2-tornado, is given in a companion study

El passat 28 de Juliol del 2007 es va inaugurar oficialment la torre instrumentalitzada per a la mesura de corrents de llamps del Niu de l’Àliga (Alp, 2537 m). Aquesta torre és actualment la cinquena torre actualment operativa en el món, fet que la fa especialment interessant. A més de la mesura de corrents de llamps, també s’hi realitzen observacions de fenòmens lluminosos a l’alta atmosfera i, per altre banda, mesures de tensions induïdes per els llamps en línies aèries. El present article presenta la evolució i un recorregut per aquesta estació de mesura.

The features of lightning flashes occurring on tall structures can give some valuable information about their initiation, especially the cases of upward flashes for lightning protection of tall structures such as wind-turbines. More than 300 flashes which struck the Gaisberg tower (Austria) have been analyzed in order to investigate differences in occurrence conditions between winter and summer. More flashes struck the tower in winter unlike the Austrian lightning activity is much lower during this season. These winter flashes deposit to ground more electrical charge than summer ones. The median values of the -10 ºC isotherm altitudes during winter are 2-km lower than during summer. This difference would produce stronger electric fields at ground level which could favor the triggering of upward flashes.

During last three summers a thunderstorm and lightning related electromagnetic fields measuring campaign were carried out over Catalonia (N-E of Spain). In these campaigns electric and magnetic fields were recorded under and in the vicinities of thunderstorms. The first part of this manuscript presents the measurement campaigns, the equipment employed, available data for posterior analysis such as lightning location data and meteorological radar; and results. Then radar and lightning data of the August 22th of 2003 episode were five sprites were observed is presented and discussed.

Knowledge of lightning parameters related to electrical atmospheric discharges are essential to predict the severity such as over voltages in power lines or other damages. Today the availability of statistical data related to lightning is still important in order to infer the severity of particular situations such as an engineering design. One of the lightning parameters useful for engineering is the total electric charge related to the entire flash. This paper presents estimations of the total charge deposited by lightning as a result of the analysis of the electric field changes due to lightning.

Els mecanismes d'electrificació d'un núvol, basats en l'intercanvi de càrregues elèctriques entre partícules, avui en dia encara no són perfectament coneguts. Les teories formulades fins ara s’ocupen d’alguns dels processos que intervenen en l’electrificació, però manca una teoria general capaç d’explicar l'elevada electrificació que hi ha en un núvol de tempesta.

Durante el verano del 2003 se realizó en Cataluña una campaña de medidas de campo electrostático y eléctrico en situaciones de tormenta. La finalidad de esta campaña fue la recolección de datos de campo eléctrico característicos de las tormentas y especialmente de los rayos.

The natural earth electric field is disturbed when a thundercloud is present, the evolution of the electrification before a lightning discharge gives enough time to do actions against possible lightning damages. Different terrain orography and nearby objects disturb the natural electric field so at each place the criteria to evaluate the risk is not equal. This paper presents a study of application the electric field measurement at ground level as a basis for lightning hazard warning and presents a methodology to study each particular situation.

La qualitat de subministrament elèctric, la fiabilitat dels equips i sistemes electrònics; i les comunicacions, van íntimament lligades a l'estudi del llamp des de la vessant de la compatibilitat electromagnètica.

En los equipos para ensayos de impulso de corriente, un parámetro fundamental para el dimensionamiento de estos es la energía aportada al ESE (Equipo Sometido a Ensayo) la cual tendrá que ser previamente almacenada en el generador. En este documento se expone el cálculo y se ofrecen unas gráficas para la determinación de los componentes del circuito generador en cada configuración de tiempos característicos en diferentes tipos de impulsos de corriente.

The main objective of this study was to give insight into the temporal and spatial aspects of lightning activity during the life cycle of diverse types of thunderstorms, and to examine the possible relationships with thunderstorm environment and meteorological radar products in order to support forecasters’ decisions about severe storms.

This study presents an analysis of a severe weather case study that took place during the early morning of the 2nd of November 2008, when intense convective activity associated to a rapidly evolving low pressure system affected the southern coast of Catalonia (NE Spain).

In this paper we present the analysis of one specific thunderstorm, which occurred during the night of 17th to 18th December 2007 in the western Mediterranean Sea, in the coastal area of Catalonia (NE Spain) (Fig.1).

During summers 2003 and 2004 a measurement campaign was carried out over Catalonia (N-E of Spain). In these campaigns, lightning electrostatic field as well electric and magnetic fields were measured. This paper describes a simple method to estimate the return stroke current for nearby strokes. The method presented analyzes the electrostatic component of the electric field to approach the return stroke current waveform.

Aquest estudi presenta una anàlisi d’un episodi de temps sever que va tenir lloc la matinada del 2 de novembre de 2008, quan la costa sud de Catalunya va estar afectada per una intensa depressió que va dur associada una important activitat convectiva. El marc i temps sever, igual que en diversos casos anteriors estudiats a la zona (Bech et al. 2007, Aran et al. 2009, Mateo et al. 2009). L’objectiu és documentar les condicions sinòptiques i mesoescalars de l’episodi així com una anàlisi amb dades radar i d’observacions de sinòptic estava dominat per una extens solc, a nivells mitjans i alts, que s’estenia des de Gibraltar al llarg de la costa del llevant peninsular fins al SE de França.

From June 2008 to March 2011 more than 400 elves have been recorded by cameras in southern France and northeastern Spain. A considerable fraction of elves are not as uniform as predicted by theory. We demonstrate examples and analyses of events displaying an asymmetrical distribution of luminosity in elves, gravity wave patterns, and even elves not recognizeable as a ring, and a distinct meteor trail. Emissions were enhanced by the meteoric dust deposition. The observations imply that the conditions in the lower ionosphere significantly influence the luminosity output. Furthermore, certain elves were accompanied by unusual electromagnetic signals, and we discuss the symmetry of their polarity, meteorology and land/sea differences.

A detailed analysis of two lightning flashes is presented. High speed video, total lightning detections and electric field measurements are the basis of the study. In general, the observed negative cloud-to-ground flashes do not produced many VHF detections . In the negative flash, most of the detections are given in the fast increase of electric field at the beginning of the dart leader. An intriguing feature during negative leaders is the fast illumination of some branches especially at the time when the leader is approaching the ground. In the case of positive cloud-to-ground flashes, a frenetic recoil leader activity occurs before the return stroke. In the presented case, recoil leader rates increase before the return stroke. The VHF network reported a large amount of detections. Those detections are not correlated with recoil leaders but with continuous current transfer to the ground.

This paper presents the analysis of various combinations of data sets with the purpose of evaluation of lightning warning methods. The data sets include CG flashes, IC sources, radar reflectivity and, for some specific cases, electrostatic field recorded at ground level.

On 29-30 October 2013, a low-light video camera installed at Pic du Midi (2877m), recorded transient luminous events above a very active storm over the Mediterranean Sea. The minimum cloud top temperature reached -73°C, while its cloud to ground (CG) flash rate exceeded 30flmin-1. Some sprite events have long duration and resemble to dancing sprites. We analyze in detail the temporal evolution and estimated location of two series of sprite sequences, as well as the cloud structure, the lightning activity, the electric field radiated in a broad range of low frequencies, and the current moment waveform of the lightning strokes. (i) In each series, successive sprite sequences reflect time and location of corresponding positive lightning strokes across the stratiform region. (ii) The longer time-delayed (>20ms) sprite elements correspond to the lower impulsive charge moment changes (iCMC) of the parent strokes (

Five gigantic jets (GJ) have been recorded by a camera on March 7th 2010, at a very closedistance above an isolated tropical storm east of Réunion Island. Three of them were produced within about 4 minutes before the storm reached its coldest cloud top temperature (-81°C), and two others occurred during the extension of the cloud. The GJs tops have been estimated between 80 and 90 km. According to ELF data recorded at Nagycenk (Hungary), all GJs are negative. The GJs are accompanied by long continuous cloud illumination and they are preceded and followed by intermittent optical flashes from the cloud. The jet duration ranged from 333 ms to 850 ms while that of the leading jets markedly varied from 33 to 167 ms and that of the trailing jets ranged from 300 to 683 ms. The trailing jet exhibits a continuous decrease of luminosity in different parts of the jet (lower channel, transition zone and for most events carrot sprite-like top) and in the cloud. The lowers channels (~20-40 km altitude) produce blue luminosity which decreases with altitude and becomes more and more diffuse with time. The transition zone (around 40-65 km) consists of red luminous beads slowly going up (~ 104 m s-1), jet channels.

This paper presents an analysis of lightning warnings based on Cloud to Ground flashes information provided by the Colombian lightning locating network (RECMA) during five years. Predictions made in this analysis have been carried out based on the two areas method. The warnings are evaluated in the basis of four parameters: Effective Alarm (EA), Failure to Warm (FTW), False Alarm (FA) and Lead Time (LT).