Lightning is a highly energetic electric discharge process in our atmosphere, evolving in several complex stages. Lightning is recognized as an essential climate variable, as it affects the concentration of greenhouse gases. It also threatens electrical and electronic devices, in particular, on elevated structures like wind turbines, and it endangers aircraft built with modern composite materials with inherently low electric conductivity. During the past decades, our fundamental understanding of atmospheric electricity has continued to evolve. For example, during the past 30 years, discharge processes were discovered in the atmosphere above thunderstorms, the so-called transient luminous events (TLEs) in the stratosphere and mesosphere, and terrestrial gamma-ray flashes (TGFs), accompanied with beams of photons, electrons and positrons, were observed from low orbiting satellites passing over thunderstorms. Lightning-like discharges also appear in plasma and high-voltage technology. The SAINT network was formed to bring the different research fields together. SAINT was the “Science And INnovation of Thunderstorms” Marie Skłodowska-Curie Innovative Training Network of the European Union Horizon 2020 program. From 2017 to 2021, 15 PhD students observed lightning processes from satellites and ground, developed models and conducted laboratory experiments. The project bridged between geophysical research, plasma technology and relevant industries. The paper presents a summary of the findings of the SAINT network collaboration.

AbstractThe spatial atmospheric pressure field due to Storm Ciarán is investigated in the south‐east of the UK at high temporal and spatial resolution using data from roadside sites. During Ciarán’s passage, a reduction in the boiling point of water was measured at Reading, from which a wider effect on the boiling point of water associated with Ciarán was calculated for the populated regions of the southeast and London. For many people in this region on 2 November 2023, the boiling point of water at breakfast time would have been below the recommended temperature range for optimal brewing of tea.

Volcanic lightning detection has proven useful to volcano monitoring by providing information on eruption onset, source parameters, and ash cloud directions. However, little is known about the influence of changing eruptive styles on the generation of charge and electrical discharges inside the eruption column. The 2021 Tajogaite eruption (La Palma, Canary Islands) provided the rare opportunity to monitor variations in electrical activity continuously over several weeks using an electrostatic lightning detector. Here we show that throughout the eruption, silicate particle charging is the main electrification mechanism. Moreover, we find that the type of electrical activity is closely linked to the explosive eruption style. Fluctuations in the electrical discharge rates are likely controlled by variations in the mass eruption rate and/or changes in the eruption style. These findings hold promise for obtaining near real-time information on the dynamic evolution of explosive volcanic activity through electrostatic monitoring in the future. The electrical activity in an eruption column is influenced by mass eruption rate and eruptive style and could therefore be used to monitor eruption evolution, according to an analysis of electrical signals from the 2021 Tajogaite eruption, La Palma

Constructive interference of lightning-generated signals in the extremely low frequency (ELF) below 100 Hz is the source of a global electromagnetic phenomenon in the Earth’s atmosphere known as Schumann Resonances (SR). SR are excited at frequencies of 7.8, 14, 20, 26, … Hz, and their diurnal and seasonal intensity variations are largely dependent on changes in the location and magnitude of the major lightning centres in Southeast Asia, Africa, and South America. In the last five decades, extensive research has focused on reconstructing the spatial and temporal evolution in global lighting activity using SR measurements, and more recently on analysing the links to climate change, transient luminous events (TLE), and biological systems. In this study, a quasi-electrostatic antenna, primarily designed as a thunderstorm warning system, is for the first time applied to measure background variability in the SR band at an urban site in Southwest England. Data collected continuously from June 2015 for a 5-year period are suitably filtered and analysed showing that SR is the dominant contribution to the fair-weather displacement current measured by the sensor in the band 10–45 Hz. Diurnal and seasonal signal amplitude variations have been found to be consistent with previous studies and show the African-European lightning centre to prevail due to the shorter source-observer distance. Also, it is shown that long-term global changes in the ocean and land temperature, and the subsequent effect on the major lightning hotspots, may be responsible for the inter-annual variability of SR intensity, indicating that the largest increase occurred during the 2015–2016 super El-Niño episode.

Lightning occurrence at higher latitudes in northwestern Europe is by far less frequent than mainland continental and the Mediterranean during most of the year. Yet, as recent studies suggest, this region harbors a large fraction of the most energetic lightning flashes on Earth, commonly referred to as superbolts. In this study, we examine the time/locations of intense cloud-to-ground (CG) strokes (> 200 kA in absolute value), provided by Meteorage for the 10.5-year period (from Jan 2010 to Jul 2020), to present a high-resolution map of their distribution, pointing out relevant discrepancies observed between -CG and + CG, respectively. We additionally investigate the potential of superbolts to result in short-lived optical phenomena above thunderstorms, collectively known as transient luminous events (TLEs). Observations in the region indicate that isolated superbolts with substantial charge moment change can produce sprites during low active marginal winter thunderstorms, in the absence of concurrent IC/CG activity several minutes before and after the event. An example is described when 3 sprites were captured in a similar context during the night of 7th/8th February 2016. We suggest that: i) convergence and aerosols advection from sea surface and busy shipping lanes may favour deep convection and cloud electrification on the English Channel with respect to surrounding areas. Inherent differences in cloud charge structure of sea based storms could lead to faster negative leader vertical velocity than those for storms over land, on average, and hence in larger peak currents, determining the winter peak of negative superbolts in the area; ii) areas occupied by the most populated superbolt clusters can be used to conduct future research in the region, aimed at better characterising microphysical properties of superbolts and their potential in generating TLEs.

Volcanic lightning is commonly observed in explosive volcanic eruptions of Volcanic Explosivity Index (VEI) > 2 and can be detected remotely providing real-time volcano monitoring information. However, little is known about the electrical activity accompanying the lower-magnitude spectrum of explosive eruptions, often involving mafic magmas. We narrow this gap in knowledge by presenting the electrical signature of the explosive activity (VEI ≤ 1) of Stromboli volcano (Italy) recorded by an electrostatic thunderstorm detector. The persistent eruptive activity of mild Strombolian explosions is occasionally interrupted by larger-scale major explosions and paroxysmal events.Here, we present electrical observations of three major explosions and unprecedented measurements of the 3 July 2019 paroxysm. The electrical signals of the major explosions show apparent similarities, with movements of charge and tens of electrical discharges, arising the question of whether these observations could be used to supplement the classification scheme of explosions on Stromboli. The electrical signals from the 3 July 2019 paroxysm exceed those from the major explosions in amplitude, discharge rate and complexity, showing characteristic variations during different phases of the eruption.These results show that also impulsive lower-magnitude explosions generate detectable electrical activity, which holds promise for monitoring low VEI activity at mafic volcanoes.

Very low frequency and wide-band lightning detection networks can detect major volcanic plumes via their intense electrical and lightning activity. However, the high number of non-detected explosive episodes confirmed by direct observations, reveals the limits of these systems in the detection of the more frequent smaller ash-rich explosive events. Here, we use a data-efficient thunderstorm detector to observe electrical discharges generated from July 2018 to January 2020 by the persistent Vulcanian activity of Minamidake crater at Sakurajima volcano in Japan. Two thunderstorm detectors recorded the electrical activity produced by explosions at Minamidake crater from a distance of 3 and 4 km from the active vents. The instruments measured the induced current due to the change in electric field with time within the extremely low frequency range (1-45 Hz). Using a volcanic lightning detection algorithm together with the catalogue of volcanic explosions compiled by the Japan Meteorological Agency (JMA) and Tokyo Volcanic Ash Advisory Center (Tokyo VAAC), the number of electrical discharges, the electrical discharge rate and the total amount of measured voltage were determined for each individual explosive event. In addition, the start of the electrical discharges was compared to the explosion onset as provided by the JMA (with a one-minute time resolution). The sensors detected electrical discharges in 71% of the 724 recorded explosions. Our detection algorithm successfully recognises the presence/absence of electrical discharges with an accuracy of 73%. We find a non-linear positive correlation between the number of discharges and the plume height. Moreover, we find that the maximum electrical discharge rate and the maximum amount of measured voltage by a single discharge also increase with plume height. Fracto- and tribo-electrification appear to be the dominant plume electrification mechanisms. Even for the few explosive events that exceeded the -10 degrees C isotherm, the timescale of electrical activity seems to be too short for ice nucleation to make a significant contribution to the plume electrification. Finally, for 12% of the electrically-active explosive events, discharges were detected by the sensors more than a minute before the JMA explosion onset. Our results show the capability of our detectors in pinpointing the inception of electrified explosive episodes in real-time and in providing an indication of the magnitude of each explosion, demonstrating their effectiveness as a cost- and data-efficient instrumentation for the monitoring of explosive ash emissions at active volcanoes. (C) 2021 The Author(s). Published by Elsevier B.V.

We show for the first time that elves can be produced by an unusual small‐scale continental spring‐time thunderstorm. The storm occurred in Central Europe, covered a very small area of ∼50 × ∼30 km and lasted only for ∼4 h on April 2, 2017. The fraction of intense positive cloud‐to‐ground lightning strokes was unusually high, reaching 55%, with a mean peak current of 64 kA. The peak currents of return strokes (RS) associated with elves exceeded ∼300 kA. Elves and their causative RS have been observed with different optical and electromagnetic recordings. Signatures of ionospheric disturbances indicating the presence of elves were found in measurements of displacement currents, ionospheric reflections of sferics and man‐made narrow‐band transmissions. All these electromagnetic observations coincide with four optical detections of elves and strongly suggest the occurrence of two more elves later in the decaying phase of the storm. Surprisingly, the same electromagnetic measurements indicate that other strong strokes did not produce any elves. Our simulation results show that the formation of an elve is not only determined by the high‐peak current of their causative strokes but that it is also controlled by the conductivity of the lightning channels and velocity of the current wavefront. We hypothesize that because of a lower conductivity of RS lightning channels and/or slower current waves only very strong strokes with peak currents above ∼300 kA might have been capable to produce observable elves during this thunderstorm.

During the night of 26-27 May 2017, a mesoscale convective system (MCS) rapidly developed over Cornwall and Devon in the South West of England, producing about 3500 lightning flashes in 3 h and 23 sprites. The MCS-type storm was characterised by a circular shape with a size of about 52,000 km(2) (cloud top temperature lower than 40 degrees C) and a local minimum in the CG flash rate (-15 min-1), when most of the sprites were observed. The mean intensity of the sprite parent CG strokes was exceptionally high in this case (+170 kA), while the associated charge moment changes ranged from 600 to 2000C km. Two identical detectors, located at different sites in southern England, measured the quasi-static displacement currents induced on metallic electrodes when exposed to the changing atmospheric electric field produced by the storm's discharges. A series of coincident large amplitude short-peak transients, some of which associated with the sprite-producing strokes, were recorded on these detectors. A multi-instrumental analysis of the lightning events producing transient current "spikes" on the electrodes revealed a significant bias towards large peak currents exceeding 100 kA, but only a minor dependence on the impulse charge moment change (iCMC) for those associated with the sprites. We suggest that the current spikes may be induced by a coupling with the electromagnetic impulse radiated by intense lightning discharges. The ease in discriminating such signatures makes the method suitable for monitoring the occurrence of powerful lightning, potentially associated with night-time transient luminous events (TLEs), thereby avoiding the limitations inherent to optical observations and radio noise affecting other receivers.

Lightning occurrence throughout Europe is at a minimum in winter and mostly confined around the coastlines of the Mediterranean. Limited extent winter thunderstorms at higher latitudes are nevertheless found to produce intense CG strokes that may result in short-lived optical phenomena above thunderstorms in the region between the stratosphere and the lower ionosphere that are collectively referred to as transient luminous events (TLEs). Recent examples of sprite observations have been reported in northern Europe, at latitudes larger than about 49N, during very low flash-rate and small-scale winter storms. This study focuses on the characteristics of the sprite-producing strokes and the context in which they occurred. The sprite parent strokes are identified through the Météorage lightning detection network, providing additional information on the polarity and the peak current. A further characterization of the electromagnetic signal associated with these events is performed combining data from a series of quasi-electrostatic lightning sensors deployed in UK, a wideband ELF-VLF-LF radio receiver at the University of Bath (UK) and an ELF station in Poland, used for the calculations of the related current moment waveform (CMW) and charge moment change (CMC). The characteristics of the thunderstorm, as the cloud top temperature (CTT), the size and the meteorological context, are considered in order to better understand the conditions leading to the observed events.

During the last decade, a large number of sprites were observed thanks to low-light video cameras located in southern France, especially at Pic du Midi (2877 m) in the Pyrénées mountain range and at the Albion Plateau (1000 m) in the south-east of France. Sprites are Transient Luminous Events (TLEs) consisting of streamer discharges, that develop at the base of the ionosphere and whose structure, size and brightness are very variable according to the density and the dynamics of these streamers. The largest type is called jellyfish or « A-bomb » sprite, and it corresponds generally to a very impulsive return stroke. Among more than 3000 sprite events in the database, we selected a few cases with large size and very strong light emission. The goal is to determine the characteristics of the flashes that produced them and the storm context in which they occurred. Thus, we analyse the video imagery, the thundercloud structure, the current moment waveform of the lightning strokes, the radiations at various frequencies from the lightning flash. We show that such very bright sprites can occur above thunderstorms at any period of the year. The favourable conditions for their production seem to be stationary thunderstorms and one case of storm produced five of them. All cases of these sprite events are associated with a halo and they are produced with a very short delay after strong positive cloud-to-ground strokes. The peak current of these strokes is about 150 kA in average and their iCMC values can reach close to 2000 C km. The leader processes and the stroke location in the thundercloud are analysed in detail for some cases.

Volcanoes are increasingly better monitored around the world. Nonetheless, the detection and monitoring of volcanic ash plumes remains difficult, especially in remote areas. Intense electrical activity and lightning in volcanic plumes suggests that electrical monitoring of active volcanoes can aid the detection of ash emissions in near real-time. Current very low frequency and wide-band thunderstorm networks have proven to be able to detect plumes of large magnitude. However, the time delay and the relatively high number of non-detected explosive episodes show that the applicability of these systems to the detection of smaller (and often more frequent) ash-rich explosive events is limited. Here we use a different type of thunderstorm detector to observe electrical discharges generated by the persistent Vulcanian activity of Minamidake crater at Sakurajima volcano in Japan. The sensors consist of two antennas that measure the induced current due to the change in electric field with time. In contrast to the current thunderstorm networks, these sensors measure within the extremely low frequency range (1-45 Hz) and can detect lightning up to 35 kilometres distance. Two detectors were installed at a distance of 3 and 4 kilometres from Minamidake crater and recorded almost continuously since July 2018. Within this period, the ash plumes reached a maximum height of 5.5 kilometres above the crater rim. Using a volcanic lightning detection algorithm and the catalogue of volcanic explosions compiled by the Japan Meteorological Agency (JMA), the number of electrical discharges was determined for each individual explosive event. In addition, the start of electrical discharges was compared to the eruption onset estimated by the JMA. Preliminary results show that the detector closest to the crater had the highest detection efficiency. It detected electrical discharges during 60% of the eruptions listed by the JMA. This is significantly higher than for the World Wide Lightning Location Network, which detected electrical discharges (in the very low frequency range) within 20 kilometres of Sakurajima for less than 0.005% of the eruptions. Furthermore, the results show that for 40% of the detected eruptions, electrical discharges were detected before the estimated JMA timing. Hence, electrical discharges can mark the inception of the explosion with a higher precision and are an indication of ash emission. This demonstrates the value of the cost-effective sensors used here as a monitoring tool at active volcanoes.

Lightning has previously been observed to disturb the lower ionosphere. These lightning-induced ionospheric perturbations were observed as disturbances on subionospheric low-frequency radio wave propagation with fast rise times <3s and gradual recoveries of duration >10s. Most of these disturbances were observed during night time when ionospheric conditions are most favorable. Here, a daytime perturbation in the lower ionosphere was observed using subionospheric radio remote sensing. The disturbance exhibits a similar to 60 s rise time with a gradual recovery of >200s. No cloud to ground lightning was coincident with the disturbance onset, however, the intracloud lightning activity of a thunderstorm over the radio receiver was seen to increase at the time of the disturbance. Therefore, the observed disturbance is unlikely to be caused by lightning, yet appears to be associated with the thunderstorm. It is proposed that this disturbance is produced by a pronounced increase in updraught strength that produced a significant change in the quasi-static electrification of the thunderstorm. This change in electrification is evident in the increase in the intracloud lightning activity of the thunderstorm. The observation provides further evidence of the ionospheric heating effect of thundercloud charge which has implications for lower atmosphere-ionosphere energy coupling and possibly sprite initiation.

Volcanic plumes become electrically charged, often producing spectacular displays of lightning. Previous research has focused on understanding volcanic lightning, primarily the large electric fields produced by charging of ash particles. Here we report on the previously overlooked phenomenon of volcanic plume electrification in the absence of detectable ash. We present the first in situ vertical profile measurements of charge, thermodynamic, and microphysical properties inside predominantly gaseous plumes directly above an erupting volcano. Our measurements demonstrate that substantial charge (at least ±8,000 pC/m3) is present in gaseous volcanic clouds without detectable ash. We suggest that plume charging may be enhanced by the emission of radon gas from the volcano, which causes ionization. This presents a hitherto unrecognized, but likely to be common, mechanism for charge generation in volcanic plumes, which is expected to modulate plume characteristics and lifetime. This process is currently neglected in recognized mechanisms of volcanic plume electrification.

Atmospheric potential gradient was measured at three sites within the Bristol area of the UK between 19th May and 24th June 2016. Two sites were on rooftops within the city of Bristol, 800 m apart from each other, while the third was in a rural location 17 km to the south. Potential gradient measurements at the two rooftop urban sites showed great temporal similarity, implying that a rooftop measurement may be assumed to represent the local urban area. Frequency domain analysis indicated a half-day cycle in the urban sites that was not observed in the rural site, consistent with other studies showing the effect of traffic aerosol on potential gradient measurements. The correlation between the two urban sites was not affected by an increase in aerosol concentration. Removal of data during rainfall, as well as one hour before and after rain, removed some of the larger changes in potential gradient typical of disturbed weather. However, large changes of potential gradient still existed, showing that rainfall alone should not be relied upon as an indicator of a non-fair weather potential gradient.