Fog, a reduction in visibility caused by water droplets suspended in the atmosphere, is a weather phenomenon which is linked to atmospheric electrical changes. Measurements of the potential gradient (PG) in particular have been shown to be useful for predicting fog, which has important applications for the aviation industry. The underlying theory behind these changes in PG during and before fog events is still an area of active research. Previously, in many studies of fog and atmospheric electricity, it has been assumed that fog droplets are neutral, for simplicity. However, it is well known that many clouds contain significant layers of space charge, and it is likely that fog droplets may also be charged. In this work, the distribution of charge in fog is studied using both numerical modelling and real-world measurements.
Numerical investigations use an earth-electrode model, in which it is assumed that the earth is a negatively charged surface and that there is a vertical electric field in the atmosphere above the surface. Using a system of 1D electrostatic equations, the steady-state distribution of vertical charge can be found, both in clear air and in a foggy air with prescribed aerosol. The results of these simulations provide the expected electrical charge in an idealised setup, which show appreciable space charge near the surface of the earth, as well as a rapidly decreasing PG with height.
Real-world measurements of the vertical charge distribution in fog up to 55m are made using a miniature electrode sensor and battery powered datalogger which is attached to a tethered balloon. The electrode current is amplified, and changes are apparent if the balloon passes through a sharp vertical gradient in space charge. As a result, vertical profiles of the magnitude and polarity of space charge in the fog layer can be measured and then compared with the modelled ideal case. In this presentation, we will show the measurements made during several fog cases with this setup.
A better understanding through modelling and measurements of the space charge in fog will help to identify cases where PG is especially well suited to fog prediction.
How to cite: Miller, C., Nicoll, K., Westbrook, C., and Harrison, R. G.: Investigating vertical distribution of charge in fog through tethered balloon measurements and modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10228, https://doi.org/10.5194/egusphere-egu25-10228, 2025.
We report the characteristics of a new multi-year atmospheric electricity data set obtained in a suburban area in Northeastern Germany, a region where comparable measurements have been missing so far. Specifically, a CS110 electric field mill (Campbell Scientific) operates since March 2021 as part of a small weather station located at the Herrenkrug campus of Magdeburg-Stendal University of Applied Sciences in Magdeburg, Germany (52.13939°N, 11.67628°E) at an altitude of approximately 50 m a.s.l. Continuous measurements have since been undertaken at 1-minute temporal resolution, providing valuable data on local atmospheric Potential Gradient (PG) variability and their linkages with Global Electric Circuit (GEC) characteristics.
PG values recorded at the site range from -1 to 1 kV/m. Typically, during undisturbed weather conditions, diurnal variation of the PG shows a single maximum and ranges between 5 and 20 V/m. On most days, there is a noticeable drop around 6-7 UTC, followed by a maximum around 14-15 UTC. Measurements from Magdeburg demonstrate an unusually small range of daily variations compared to other sites. While theoretically expected PG values under fair weather conditions should be around 100 V/m, the local instrument has never reached such values. Recent PG measurements performed at three different stations of the GLOCAEM network with an identical instrument showed median PG values in a range between 60 and 240 V/m during unperturbed conditions (Nicoll et al. 2019), while our measurements exhibited a median value of only 13.5 V/m, demonstrating that both PG median amplitude and variability obtained at the site are smaller than would be expected.
To further investigate this issue, a short campaign with parallel measurements using an identical reference instrument has been undertaken during summer and fall of 2024. Since the original field mill is located inside a fenced area, it might be expected that the surrounding metallic fence negatively affects the measurements. By conducting parallel measurements with the reference field mill also being placed inside the fenced area, we however did not find significant systematic effects of the fence on the measured PG values.
A second series of measurements was conducted at about 200 m distance from the original field mill, where the surrounding area was relatively clear from any trees and built infrastructure. Measurements at this site have been obtained under different weather conditions. While there exists considerable co-variability between both sites during most of the day, we found much larger, even qualitative differences between both instruments arising during sunrise and sunset.
The results of our parallel measurements contribute to identifying discrepancies between co-located electric field measurements, which have also been reported in other previous studies, and clarifying the underlying root causes. To this end, the reference measurements during daytime have been used to determine a statistical correction for the values obtained with our primary instrument, which will be further employed for calibrating our ongoing measurements. The thus obtained long-term time series of local PG variations provides a new dataset allowing further detailed studies of atmospheric electricity variations in suburban areas of Central Europe.
How to cite: Karapetyan, G., Donner, R. V., Nicoll, K., and Mkrtchyan, H.: A new multi-year data set of Potential Gradient variations at a suburban site in Northeastern Germany , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12436, https://doi.org/10.5194/egusphere-egu25-12436, 2025.
High latitude measurements of the atmospheric Potential Gradient (PG) can provide valuable information on understanding sources of variability in the Global Electric Circuit (GEC). The influence of solar activity on electrical processes (such as ionisation) is much greater at high latitudes, allowing the mechanisms by which space weather affects atmospheric electricity to be studied. The often cleaner environment, which means that PG measurements are not dominated by variations in local aerosol concentrations, also means that processes related to changes in near surface ionisation (e.g. from radon) can be studied.
Measurements of PG have been made at a high latitude site in Sodankyla, Finland (67°22' N, 26°38' E) since 2017 using a Campbell Scientific CS110 Electric Field Mill. Sodankyla is a heavily instrumented site for meteorological, geophysical and auroral research and so a wealth of additional observations are available to support PG analysis. This research provides an overview of 7 years of PG measurements at Sodankyla, including analysis of the typical fair weather diurnal variation, which demonstrates clear evidence of the GEC signal, with a morning minimum and evening maximum, with significantly larger PG values during summer months than winter. This work will also analyse the diurnal and seasonal variability in PG at Sodankyla alongside the variability in co-located ionisation measurements, comprising observations of Radon222, as well as “external” radiation from a gamma ray spectrometer which is sensitive to gamma emission from natural radioactivity as well as galactic cosmic rays. This work will contribute to understanding around how conductivity variations resulting from changes in local ionisation rate contribute to diurnal and seasonal variability in PG at clean air sites.
How to cite: Nicoll, K., O'Neill, O., Miller, C., Paatero, J., and Ulich, T.: Understanding variability in atmospheric electricity measurements at Sodankyla, Finland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13547, https://doi.org/10.5194/egusphere-egu25-13547, 2025.
From rubbing a balloon on one's hair to the dramatic display of volcanic lightning, the triboelectric effect is a widespread phenomenon where contact between objects leads to an exchange of electric charge. Despite its ubiquity, our understanding of the underlying physics remains largely phenomenological. Among the many open questions, one is particularly relevant to earth science and astrophysics: why do objects made of the same material continually exchange electric charge? This effect is especially pronounced in systems involving grains or powders, where frequent collisions can result in a significant buildup of electrostatic potential energy. Such processes can influence the dispersal range of aerosols in the atmosphere, determine whether protoplanetary dust will coalesce, and even trigger thunderstorms during volcanic eruptions or forest fires. Using acoustic levitation, we isolate individual grains and conduct controlled collisions with a substrate, measuring the charge by observing the grain's behavior in electric fields. This method can accurately resolve individual collision events, allowing us to investigate various proposed charging mechanisms and explore in detail what causes the breaking of symmetry between positively and negatively charging samples. We determine that slight variations in surface composition due to molecules recruited from the atmosphere can lead to drastic changes in the charging behavior.
How to cite: Grosjean, G. and Waitukaitis, S.: Investigating the origins of static charge in granular systems of silica and other oxides using acoustic traps, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10837, https://doi.org/10.5194/egusphere-egu25-10837, 2025.
Dust storms have been observed to generate significant DC electric fields. Dust devils specifically are a subset of dust storm, with an ordered sense of rotation about a central axis. Observations in Arizona and Nevada have recorded both electric and magnetic fields associated with dust devils. These electromagnetic signatures are important for future space exploration, with charged dust presenting issues for solar power generation and optics as well as the possibility of communication disruption. The likelihood of lightning from dust devils also has implications for the origin of life, and the chemical composition of the Martian surface and atmosphere.
Building upon terrestrial observations of dust devils, and other properties of triboelectrically charged particles, a lumped particle methodology for the generation of electromagnetic fields based on fundamental laws of physics is presented. In this model, the particle motion is constrained to a simple harmonic motion, tracing a circle in 2D, with parameterised relationships for the height variation of the dust devil, the charge profile with grain height and the velocity of the rotational motion determined.
Results from the simulation of a dust devil with 3.5 metre radius are compared to the measurements from a terrestrial dust devil of the same size. With a tuned surface electron density input to an event-driven tribocharging model, calculated electrical and magnetic fields are within a factor of two of the measured values. An idealised 3.5 m radius dust devil with its centre passing directly over magnetic and electric field sensors, has an electric field approaching the terrestrial breakdown field strength. This is consistent with recent observations of electric discharge in the vicinity of a dust devil in the UAE. The vertical and horizontal variation of the electric and magnetic field in the vicinity of the dust devil can now be predicted, and the model can readibly be used to interpret field observations on Earth, lander measurements on Mars, and predict signals in future instrument deployments to inform sensor design.
How to cite: Reid, D., Aplin, K., and Teanby, N.: Simulating Electric and Magnetic Fields from Dust Devils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12324, https://doi.org/10.5194/egusphere-egu25-12324, 2025.
Although cloud electrification and lightning have been studied for hundreds of years, the field still deals with many open questions [1]. One of the most puzzling examples is that of lightning inititation – neither the mechanism by which a cloud generates enough charge to cause lightning nor the process by which lightning itself is triggered are well understood. In our experiment we aim to gain insight into both questions on the scale of a single particle. We utilize optical tweezers to levitate individual aerosol particles and observe their charging and discharging dynamics over days-to-weeks time periods and with elementary-charge resolution. Our approach allows us to study these processes without losing information to ensemble averages or external interference from other particles or substrates [2], and is applicable to solid and liquid particles in the micrometer size range. Using multi-photon absorption from the trapping laser [3] we can charge the trapped particle at different rates and to different values, observing every charging and discharging event along the way. Additionally, the experiment allows us to control the relative humidity around the particle and to fully discharge the particle using air ions. By studying the charging behavior of the particle and the spontaneous discharges it experiences, we hope to contribute to a better understanding of the microphysical processes involved in lightning initiation and adjacent electrical phenomena in the atmosphere.
This project has received funding from the European Research Council (ERC) under the European Union’s Starting Grant (A. Stoellner, I. Lenton & S. Waitukaitis received funding from ERC No. 949120, C. Muller received funding from ERC No. 805041).
[1] J. R. Dwyer and M. A. Uman, Physics Reports 534, 147 (2014).
[2] F. Ricci, M. T. Cuairan, G. P. Conangla, A. W. Schell, and R. Quidant, Nano Letters 19, 6711 (2019).
[3] A. Ashkin and J. M. Dziedzic, Physical Review Letters 36, 267 (1976).
How to cite: Stoellner, A., Lenton, I., Muller, C., and Waitukaitis, S.: Measuring self-induced corona discharges of individual aerosol particles in an optical trap , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9659, https://doi.org/10.5194/egusphere-egu25-9659, 2025.
Electrical discharges such as lightning are among the most energetic and remarkable phenomena in planetary atmospheres. Both laboratory experiments and modeling studies have predicted that triboelectric charging of wind-blown particles in dust events on Mars should lead to significant electrification. However, there have been no direct measurements of a Martian electric field or observations of discharges. Here, using acoustic recordings from the SuperCam microphone onboard the Perseverance rover, we report evidence for an atmospheric discharge in a dust devil, based on the electromagnetic and acoustic signatures observed in the microphone signal. This is the first direct detection of a triboelectric discharge in the Mars atmosphere. It shows that the electric field in a dust devil can reach 25 kV/m, which is the expected breakdown threshold of the Mars atmosphere. Electrical discharges on Mars may have implications for dust dynamics, the chemistry of oxidants and methane in the atmosphere, and ultimately robotic and human exploration.
How to cite: Chide, B., Lorenz, R., Montmessin, F., Maurice, S., Parot, Y., Hueso, R., Martinez, G., de Vicente-Retortillo, A., Jacob, X., Lemmon, M., Dubois, B., Meslin, P.-Y., Newman, C., Bertrand, T., Cousin, A., and Wiens, R.: Search for in situ signatures of electric activity on Mars, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5745, https://doi.org/10.5194/egusphere-egu25-5745, 2025.
Wildfires pose a significant natural disaster risk to populations and contribute to accelerated climate change. As wildfires are also affected by climate change, extreme wildfires are becoming increasingly frequent. Although they occur less frequently globally than those sparked by human activities, lightning-ignited wildfires play a substantial role in carbon emissions and account for the majority of burned areas in certain regions. While existing computational models, especially those based on machine learning, aim to predict lightning-ignited wildfires, they are typically tailored to specific regions with unique characteristics, limiting their global applicability. In this study, we present machine learning models designed to characterize and predict lightning-ignited wildfires on a global scale. Our approach involves classifying lightning-ignited versus anthropogenic wildfires globally over a long timespan, and estimating with high accuracy of over 91% the probability of lightning to ignite a fire based on a wide spectrum of factors such as meteorological conditions and vegetation. Utilizing these models, we analyze seasonal and spatial trends in lightning-ignited wildfires shedding light on the impact of climate change on this phenomenon. Our findings highlight significant global differences between anthropogenic and lightning-ignited wildfires. Moreover, we demonstrate that, even over a short time span of less than a decade, climate change has steadily increased the global risk of lightning-ignited wildfires. We also find that models trained to predict lightning-ignited wildfires and models trained to predict anthropogenic wildfires are very different. This dramatically reduces the predictive performance of models trained on anthropogenic wildfires when applied to lightning-ignited ignitions, and vice versa. This distinction underscores the imperative need for dedicated predictive models and fire weather indices tailored specifically to each type of wildfire.
How to cite: Price, C., Shmuel, A., Glickman, O., Lazebnik, T., and Heifetz, E.: Prediction of Lightning-Ignited Wildfires On A Global Scale based on Explainable Machine Learning Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9775, https://doi.org/10.5194/egusphere-egu25-9775, 2025.
Lightning is a primary driver of natural wildfires globally. In mid- and high-latitude regions, summer thunderstorms are key precursors of lightning-ignited wildfires, contributing substantially to the total burned area. While the influence of meteorological conditions and fuel availability on wildfire occurrence is relatively well understood, the role of the electrical characteristics of lightning in ignition probability remains uncertain. In particular, it is unclear whether the presence of a continuing current lasting tens to hundreds of milliseconds is essential for ignition or whether it significantly affects ignition probability compared to meteorological factors and fuel availability.
In this study, we investigate the factors that increase the probability of wildfire ignition in Contiguous United States (CONUS). We investigate the meteorological conditions during the occurrence of fire-igniting flashes, the value of fire danger indices, the presence of continuing currents detected from space by the Geostationary Lightning Mapper (GLM), and the polarity of the strokes provided by the Earth Networks Lightning Total Network (ENTLN). We found that the lightning ignition efficiency of fire-igniting strokes with continuing current is slightly higher than that of lightning without continuing current. In particular, we report that strokes with continuing currents may have a higher potential to produce wildfires than cloud-to-ground strokes without continuing currents when the conditions for fire ignition and spread are less favorable. Additionally, we find that lightning strokes with continuing currents are associated with smaller burned areas, likely due to less favorable conditions for fire spread.
How to cite: Perez-Invernon, F. J., Moris, J. V., Gordillo-Vázquez, F. J., Zhu, Y., and Lapierre, J.: Assessing the Role of Continuing Current in Fire-Igniting Lightning Strokes with Space-Based Measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7039, https://doi.org/10.5194/egusphere-egu25-7039, 2025.
New geostationary satellites, together with ground networks, now provide high-resolution, continuous lightning observations, offering unprecedented insights into lightning activity across vast areas of the globe. In contrast, global climate models (GCMs) lack the spatial resolution and physical processes required to simulate lightning directly, leading to the need for parameterizations and scaling methods. In this study, we present a novel trend-based scaling approach that bridges the gap between coarse-resolution GCM output and high-resolution lightning flash rates to improve projections of lightning activity by the end of the century. The scaling method employs machine learning techniques to identify the atmospheric parameters that best reproduce observed current lightning activity, which are then combined with coarser GCM trends (individually for each quantile of the distribution) to project future lightning changes.
Italy was selected as a case study, using the past 15 years of lightning observations from the LINET network to identify lightning predictors among atmospheric parameters from the ERA5 reanalysis. The best predictors identified include a combination of convective available potential energy, relative humidity, temperature gradients, wind velocity and shear, geopotential height, and freezing level. This model accurately reproduces the spatial distribution and temporal variability of current lightning activity. Trend scaling from multiple future climate scenarios was then applied using CMIP6 projections to evaluate changes in lightning activity across different regions and time periods.
Our results show that trend-based scaling significantly improves the spatial distribution and intensity of projected lightning flash rates compared to traditional parameterizations. This work provides a practical framework for integrating lightning projections into climate impact studies, enhancing the reliability of lightning future changes under various climate scenarios. The main advantage of the proposed method is that it can be applied to reanalysis datasets of any resolution, offering a flexible tool for assessing lightning-related risks in a warming world.
How to cite: Arnone, E., Cortesi, N., Rubinetti, S., Dietrich, S., and Petracca, M.: Trend-based scaling for high-resolution lightning in climate projections , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10264, https://doi.org/10.5194/egusphere-egu25-10264, 2025.
Most tropical cyclones (TCs) landfalling Southern China originated from the Northwest Pacific (NWP) and tracked over the South China Sea (SCS) before landfall. The internal structures such as convective characteristics of the tropical cyclones may change as the TCs translate from the open ocean (NWP) to the enclosed sea (SCS) due likely to the impacts from nearby landmass. This study compares the lightning activity and convective structures, as well as the large-scale environments, of TCs over the NWP and SCS to better understand the structural changes and underlying physical mechanisms. It is interesting that TCs over SCS are much more electrically active than NWP TCs (especially in the outer rainbands), even though the NWP TCs precipitate heavier. Multi-satellite observations suggest that the NWP TCs have a deeper layer of ice particles, producing heavier surface rainfall; however, the SCS TCs own more large ice particles or supercool liquid in the mixed-phase region, which is essential for charge separation thus lightning production. It is surprising that the thermodynamic conditions (e.g., SST and atmospheric instability) of the NWP are more favorable for convective development than SCS. A few factors may contribute to higher lightning activity in SCS TCs, including stronger vertical wind shear, thinner warm cloud depth and higher aerosol optical depth, all may help to produce asymmetric intense convection and active mixed-phase processes. Furthermore, SCS TCs display a marked lightning maximum in the front quadrants of the moving direction, but NWP TCs are less so, likely because the thermodynamic and aerosol impacts from land are stronger in the SCS. Lightning in the SCS TCs is also more asymmetric relative to the vertical wind shear than the NWP TCs, which is featured by a maximum in the right of the downshear region of the outer rainband (opposite to the precipitation pattern).
How to cite: Xu, W. and Xie, Y.: Contrasting Lightning Activity and Convective Structures between Tropical Cyclones over Open Ocean and Enclosed Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14349, https://doi.org/10.5194/egusphere-egu25-14349, 2025.
Recently, detailed spatio-temporal analysis, using X-band multi-parameter radar-derived 3D volume scan and total lightning data in Japan, have revealed the peak in-cloud (IC) lightning occurs ~10 mins before maximum ground precipitation for individual cells of a summer thunderstorm (TS) producing torrential rain. This study investigates the potential of utilizing the total lightning data for monitoring and short-term prediction of torrential rain during three summer TS events causing heavy rainfall over Japan: an isolated TS, a TS possessing a merging of two cells, and a splitting TS cell. We construct simple linear regression models using (1) only ground precipitation volume (PV) and (2) a combination of ground PV and IC pulse rate. These models are continuously updated with the latest observations of IC and ground PV values to predict the one-step and multi-step ahead values of ground rainfall. We demonstrate a promising approach for short-term prediction of ground rainfall, by simultaneous application of the current and historical data of IC pulse rate and PV, which showed high accuracy (cross-correlation coefficient between observed and predicted PV was 0.84~0.94).
How to cite: Mondal, D., Hobara, Y., Kikuchi, H., and Lapierre, J.: Assimilation of Rainfall and Total Lightning Data for Nowcasting Torrential Rainfall During Summer Thunderstorms in Japan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18235, https://doi.org/10.5194/egusphere-egu25-18235, 2025.
The UK’s goal of achieving net zero emissions by 2050 requires the construction of extensive new power infrastructure to accommodate low carbon energy technologies (e.g., offshore wind, nuclear) while mitigating climate risks. Lightning activity poses severe risks to power system security and can result in significant economic losses (Ofgem, 2019; Bialek, 2020). These risks must be mitigated as effectively as possible as new power grid infrastructure is built in the coming years and climate scenarios.
To represent lightning activity, this study employs a newly developed thunder hour dataset from Earth Networks, with a spatial resolution of approximately 5.5 km, specifically designed for climate research (DiGangi et al., 2022). Ten years of monthly historical UK thunder hour data from Earth Networks are analysed to identify lightning climatology trends and support the development of a long-term predictive lightning model. This study differentiates itself from previous UK lightning research by focusing directly on lightning risks impacting the UK’s power grid infrastructure, aiming to offer actionable insights for risk mitigation during the planning of future power assets for National Grid Electricity Transmission (NGET).
Historical lightning damage hotspots are identified by linking power system fault records with spatiotemporal lightning activity characteristics such as peak current and lightning duration from lightning detection and location networks. Analysing lightning activity’s impact on power system line trippings helps improve the grid’s reliability and safety (Li et al., 2024). The novelty of this research lies in its integration of lightning hotspot analysis, informed by lightning climatology trends, with asset distribution to pinpoint high-risk areas for electrical infrastructure, validated through power system failure case studies. These findings offer a basis for improved disaster prevention and mitigation strategies, enhancing grid resilience and safety.
Acknowledgement:
The authors acknowledge the support for the KERAUNIC project (ref: NIA2_NGET0055, National Grid Electricity Transmission, 2024), which focuses on improving the understanding of lightning-induced damage to UK power systems. This research is part of an innovation effort funded through the Network Innovation Allowance (NIA).
References:
Bialek, J. (2020). What does the GB power outage on 9 August 2019 tell us about the current state of decarbonised power systems? Energy Policy, 146, 111821.
DiGangi, E., Stock, M., & Lapierre, J. (2022). Thunder Hours: How Old Methods Offer New Insights into Thunderstorm Climatology. Bulletin of the American Meteorological Society, 103, E548-E569. https://doi.org/10.1175/BAMS-D-20-0198.1.
Li, M., Cheng, S., Wang, J., Cai, L., Fan, Y., Cao, J., & Zhou, M. (2024). Thunderstorm total lightning activity behaviour associated with transmission line trip events of power systems. npj Climate and Atmospheric Science, 7(1), 148.
National Grid Electricity Transmission. (2024). Knowledge Elicitation of Risks to Assets Under LightNing Impulse Conditions (KERAUnIC). https://smarter.energynetworks.org/projects/nia2_nget0055/.
Ofgem. (2019). Investigation into 9 August 2019 Power Outage. Retrieved from https://www.ofgem.gov.uk/publications/investigation-9-august-2019-power-outage.
How to cite: Bai, X., He, X., Fullekrug, M., Gu, C., Xu, M., Li, B., Souto, L., Chikohora, T., and Dodds, D.: Enhancing Lightning Resilience: Predictive Models and Infrastructure Protection for UK Electric Power Systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3614, https://doi.org/10.5194/egusphere-egu25-3614, 2025.
With the growing use of alternative energy generation such as wind turbines, it is important to understand their effect on the environment and, in turn, on storms. One environmental parameter that could be directly impacted by wind turbines is lightning, since tall objects can enhance lightning development. Additionally, wind turbines can potentially alter the boundary layer of storms, which can cause changes in the low-level winds within the storms and affect their evolution. Several studies have been performed focusing on the lightning trends directly over specific wind farms, the attachment and upward development of lightning from turbines, and the protection of wind turbines from lightning in general; however, few studies have performed large-scale analysis of the effect turbines have on lightning and storms. This study analyzes the trends in lightning not only occurring over the wind farms but surrounding the wind farms on both a storm level, and at larger temporal and spatial scales. For this analysis, the Earth Networks Total Lightning Network (ENTLN) and the Geostationary Lightning Mapper (GLM) provide extensive lightning datasets covering CONUS, while radar data from the Multi Radar Multi Sensor (MRMS) platform offers information on storm development. Preliminary results show a potential change in both the lightning patterns and characteristics, as well as radar echoes with storm passage over wind farms, indicating some effect may be present.
How to cite: Ringhausen, J., DiGangi, E., Lapierre, J., and Zhu, Y.: Exploring the Effect of Wind Farms on Lightning and Storm Development, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21014, https://doi.org/10.5194/egusphere-egu25-21014, 2025.
On 3 August 2021, Sandia launched a flotilla of four Heliotrope solar hot air balloons (Bowman et al., 2020) from Belen regional airport in New Mexico (USA) to coincide with the launch of the Boeing Starliner rocket. These Heliotrope balloons allow level flights between 15 and 25 km altitude for several hours from sunrise to sunset. Despite the cancellation of the rocket launch, the microbarometers on board these balloons were able to record in the stratosphere the acoustic signals emitted by eight chemical explosions and the lightning that occurred in a thunderstorm cell. This storm cell was located between 10 and 40 km from three of the four balloons.
In this presentation, we first identify the individual signals that may be due to lightning. For this we use the method proposed by Farges and Blanc (2010) for ground-based thunder measurements and by Lamb et al. (2018) for the first stratospheric balloon lightning measurements. Signal analysis has enabled us to (i) confirm that the acoustic energy of thunder decreases as the inverse square of the distance, and (ii) identify that the electrostatic mechanism of thunder production in the infrasonic range (Wilson, 1921; Dessler, 1973; Pasko, 2009) is indeed present when the observer is located just above or just below the thundercloud. One of the balloons was equipped with two microbarometers separated vertically by around 30 m. The time difference between the two microbarometers for the arrival of signals from a flash of lightning is characteristic of the angle of incidence of the wave. It can be seen that this time difference evolves as expected as the balloon moves away from the storm cell.
Finally, we show for the first time that with a network of three sensors located in the stratosphere, it is possible to give a 3D localization of the first arrival of lightning signals. An equivalent acoustic source inside the cloud is clearly identified when the discharge is of the intranuage type, whereas the acoustic source is located between the ground and the cloud when the discharge is of the cloud-to-ground type.
SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
How to cite: Farges, T., Burgos, G., Bowman, D. C., Gainville, O., Albert, S. A., and Le Pichon, A.: Characterisation and localisation of lightning by a flotilla of stratospheric balloons., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5799, https://doi.org/10.5194/egusphere-egu25-5799, 2025.
Thunderstorms are components of typhoons, linear precipitation bands and supercells, which cause severe wind and flood damage and lightning strikes. Observationally tracking the time variation in their development and decay, which is directly linked to precipitation, is important for understanding and predicting precipitation and lightning discharge activity. However, general C-band radars for meteorological use cannot observe cloud particles, and Ka-band radars require a large amount of money for maintenance because the consumable parts are expensive, and there are also limits to high-resolution observations in the vertical direction because it takes time for spatial scanning. Furthermore, it is difficult to track the occurrence and initial growth of cumulonimbus clouds from the horizontal resolution problem because the cloud top altitude cannot be geometrically obtained from geostationary meteorological satellites. The central Tokyo area is facing the risk of flooding due to the limits of its drainage capacity, and it is an urgent issue to accurately grasp the movement of thunderstorms.
Our research group has achieved results in the measurement of electrostatic fields and lightning discharge radio waves associated with thunderstorm activity in the Metro Manila, as well as in 3D cloud measurement using aircraft and satellites. In this study, we will make use of this experience to construct a system that monitors the charge separation within thunderstorm and the time-dependent changes in the three-dimensional shape of clouds. We will do this by deploying three sets of cloud stereo imaging equipment that combines field-mil electric field sensors and multiple digital cameras to surround an area with a diameter of approximately 20 km in the center of Tokyo.
How to cite: Takahashi, Y.: Development of a thunderstorm monitoring system based on atmospheric electric fields and 3D cloud imaging on the ground, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21153, https://doi.org/10.5194/egusphere-egu25-21153, 2025.
Lightning is a key atmospheric phenomenon that modulates atmospheric chemistry and impacts terrestrial carbon dynamics through the ignition of wildfires and direct tree mortality. Despite its importance, there is a data gap in publicly available global lightning datasets with high spatial and temporal resolution for scientific use. In this study, we present our progress towards creating a global gridded lightning dataset derived from Vaisala’s Global Lightning Detection Network (GLD360), covering the period from 2019 to 2024, with potential annual updates thereafter. This dataset is produced through a systematic gridding procedure that converts raw GLD360 lightning event data into 0.1º hourly, 0.25º daily, and 0.5º monthly gridded values. It includes key variables such as positive and negative cloud-to-ground and intra-cloud stroke count/density, stroke peak current, stroke location uncertainty, and flash count/density, making it valuable for a wide range of scientific applications. We are evaluating the gridded dataset using local lightning detection networks in Alaska (USA), Spain, South Africa, and the New South Wales and Australian Capital Territory (Australia). Meanwhile, we are comparing stroke density with the Global Lightning Climatology (WGLC) dataset derived from the World Wide Lightning Location Network (WWLLN) and flash density with the Lightning Imaging Sensor/Optical Transient Detector (LIS/OTD). The dataset could be particularly useful for advancing studies on lightning climatology, the role of lightning in wildfire ignition, thunderstorm identification, and other related topics. Its high spatial and temporal resolution also supports regional studies of lightning-related hazards and ecosystem impacts. Our goal is to make this dataset publicly available to the scientific community to facilitate new insights into the role of lightning in the Earth system.
How to cite: Qu, Y., Jones, M. W., Brambleby, E., Hunt, H. G. P., Pérez-Invernón, F. J., Yebra, M., Zhao, L., Moris, J. V., Janssen, T., and Veraverbeke, S.: A new global gridded lightning dataset with high spatial and temporal resolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8351, https://doi.org/10.5194/egusphere-egu25-8351, 2025.
The relationship between lightning and high-energy particles has been a hot topic in our field recently. We conducted a lightning observation campaign to investigate the characteristics of high-energy particles before and after the inception of natural lightning. The campaign utilized the Large High Altitude Air Shower Observatory (LHAASO), which is equipped with over 4,000 electromagnetic particle detectors covering a 1 km² area, capable of detecting high-energy particles with nanosecond precision. In conjunction with LHAASO, we deployed two VHF interferometers to image lightning channels with equally high resolution. Since the campaign's inception, we have captured many lightning flashes alongside synchronous high-energy particle detections. This paper presents preliminary results during the last two years, including observations of Terrestrial Gamma-ray Flashes (TGFs) and Thunderstorm Ground Enhancements (TGEs), offering new insights into the relationship between cosmic rays and lightning initiation.
How to cite: Yuan, S., Qie, X., Sun, Z., Feng, J., Wang, Z., Huang, Z., and Di, S.: Comprehensive Lightning Observation Using VHF Interferometer and LHAASO, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21881, https://doi.org/10.5194/egusphere-egu25-21881, 2025.
To better understand lightning interactions with the atmosphere, a high-speed (streak) spectrograph was used to characterise various high voltage impulses representing lightning. A Marx generator was used to produce 1.2/50 μs high voltage impulses, according to the IEC 60060 standard, ranging from 60 kV to 160 kV. The atomic emission spectrum was captured using a high-speed streak system at resolutions of 0.35 μs/pixel to 0.14 μs/pixel. Spectral data were first recorded over a broad range of 250 to 990 nm, covering a part of the ultraviolet spectrum, full visible spectrum and into near-infrared. Then three smaller bands were chosen for high resolution spectral data to enable the identification of key atomic emission lines such as Oxygen-I, Nitrogen-I and II, and Argon-I from the atmosphere, as well as Tungsten-I from the experiment electrodes. It was observed that an increase in high voltage lead to greater spectral intensity with more prominent lines, as expected, indicating an increase in energy transfer into the surrounding atmosphere. Subsequent analysis of the data resulted in both temperature and energy measurements of these arcs. Such spectral signatures have important implications for refining atmospheric electricity models and better understanding risks associated with lightning, particularly for built infrastructure, such as struck power lines and wind turbines, but also natural features, like forests and woodland. It is the intention that this work will progress onto the study of spectra from laboratory generated lightning arcs.
How to cite: Hills, M., Mitchard, D., and Peretto, N.: High-Speed Ultraviolet and Visible Optical Emission Spectroscopy of High-Voltage Impulses Representing Lightning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20073, https://doi.org/10.5194/egusphere-egu25-20073, 2025.
Lightning Mapping Array (LMA) networks detect very-high-frequency (VHF, 60–66 MHz) emissions from lightning channels inside clouds. This enables the mapping of lightning in three dimensions. The use of real-time LMA data has proven beneficial for forecasting and warning about impending severe weather. Beyond the standard analysis of cloud-to-ground lightning information, the ability to visualize 3D total lightning has provided forecasters with greater knowledge of storm-scale processes.
A network of more than 20 LMA stations has been established in Catalonia (northeastern Iberian Peninsula) thanks to a partnership between the Meteorological Service of Catalonia (SMC) and the Technical University of Catalonia (UPC). Since it began real-time operations during the summer of 2023, it has grown to become Europe's largest LMA network.
To complement classic severe weather signatures observed in weather radar (e.g., storm splitting, BWER, TBSS) and in satellite imagery (e.g., overshooting tops, v-shape), we put our focus here on severe weather signatures observed with the LMA network during the thunderstorm seasons of 2023 and 2024 in Catalonia. Indeed, lightning distribution and evolution can portray complementary information in real-time surveillance, adding confidence to the forecaster and therefore reinforcing the decision-making when issuing alerts for imminent severe weather.
How to cite: Pineda, N., Fabró, F., Rodríguez, O., Romero, D., van der Velde, O., López, J. A., and Montanyà, J.: Total lightning for the early warning: Severe weather signatures from the real-time Lightning Mapping Array network in Catalonia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6293, https://doi.org/10.5194/egusphere-egu25-6293, 2025.
The appearance of transient luminous events (TLEs) in the mesosphere is known to be associated with strong (almost exclusively) positive cloud-to-ground (+CG) strokes with large charge moment change (CMC) values in tropospheric thunderstorms. Nevertheless, despite numerous observational campaigns from ground and space-based platforms, robust theoretical models, and laboratory experiments, there are lingering open questions concerning the exact circumstances for the appearance of sprites, among which is the cause for the observed delay in sprite appearance relative to the onset of the current in the parent stroke. Curiously, seemingly identical +CG discharges with the same CMC that should lead to a mesospheric discharge do not initiate sprites, while sometimes even weaker +CG discharges are able to do so. Previous studies aiming to resolve this issue have investigated different effects, such as mesospheric inhomogeneities, the presence of meteoritic ablation products, discharges in neighboring cloud cells, associative detachment of electrons from atomic oxygen ions, and long continuing currents. Here, we investigate the properties of the parent +CG's continuing current by suggesting piecewise-varying discharge time dependence. We present the results of simulations using a 3D quasi-electrostatic model (Haspel and Yair, 2024) with various patterns of the parent flash discharge current. We show how short, moderate, and long delayed sprites can be incepted due to piecewise-varying discharge current time dependence, and how discharges possessing low iCMC values can still produce electric fields in the mesosphere with magnitudes above the conventional electrical breakdown field. The model is validated by simulating two sprite events observed from the International Space Station during the ILAN-ES campaigns in April 2022 (on AX-1) and February 2024 (on AX-3), showing how a delayed sprite is incepted by a prolonged piecewise pattern of the current in the parent +CG flash.
Haspel, C. and Y. Yair (2024), Numerical Simulations of the region of possible sprite inception in the mesosphere above winter thunderstorms under windshear. Ad. Spa. Res.., 74, 11, 5548-4468, doi:10.1016/j.asr.2024.08.050
How to cite: Yair, Y. and Haspel, C.: Simulating the possible regions of delayed sprite inception above thunderstorms using piecewise-varying lightning current time dependence , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2357, https://doi.org/10.5194/egusphere-egu25-2357, 2025.
Thunderstorm processes represent a challenge for numerical models, as they involve numerous processes of various scales, and explosive events producing exponentially increasing numbers of particles in a very short span of time. A phenomenon called a Relativistic Runaway Electron Avalanche can occur under the right conditions, and lead to the production of a Terrestrial Gamma-Ray Flash (TGF), spanning over tens of microseconds, and during which up to 1017 electrons and photons are produced for the most intense ones, the weaker ones still producing 1012 to 1015 energetic photons. While Monte Carlo models are often used to simulate such processes, runtime typically scales with particle number, which leads to poor performance without a way to limit the number of particles computed. On the other hand, a fluid model may be adapted to deal with large particle densities, but it will struggle to deal with the extreme energies and electric fields, and will lose track of the physics of individual particles, which becomes relevant when submitted to such extreme parameters.
In order to accurately and efficiently simulate all these processes, we are developing a fully parallelized 3-D hybrid model. The code is optimised for massively parallel usage on Graphics Processing Units (GPUs), and uses the AMReX library, a software framework for massively parallel, block-structured codes, allowing us to run in parallel with implemented adaptive mesh refinement (AMR), which further improves the accuracy of the model.
With this model, we are aiming at obtaining a better understanding of lightning processes and TGFs, not only in the current Earth atmosphere, but also in the atmosphere of other celestial bodies, and in mixtures likely to have existed in the environment of Primordial Earth.
How to cite: Gourbin, P., Fangel-Lloyd, E., Dujko, S., Gammelmark, M., Karlsson, S., Jara Jimenez, A. R., van Gemert, H., and Köhn, C.: Towards a hybrid model to simulate lightning and associated energetic events in various atmospheres, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8887, https://doi.org/10.5194/egusphere-egu25-8887, 2025.
Electrical processes such as lightning and transient luminous events (TLEs) are important drivers of chemical processes in planetary atmospheres, including potentially facilitating the formation of important prebiotic molecules. The numerous extrasolar planets discovered present a huge diversity in environmental conditions to explore the possible emergence of electrical processes. To this end, we adapt general circulation models to simulate these exoplanet atmospheres and study the potential emergence of electrical processes. Here, we present results from simulations of tidally locked rocky exoplanets with the Met Office Unified Model. Lightning parameterisations that use bulk cloud properties - such as cloud-top height, frozen water content, and graupel flux - are initially used to infer lightning flash rates. For tidally locked exoplanets, we find that lightning is limited to the permanent dayside hemisphere, with substantial spatial and temporal variations. We then discuss methods to determine the charge structure and thus electric field strengths in the atmospheres, that can be used to infer whether lightning flashes can be followed by TLEs. Finally, we put the electrical processes into context of the atmospheric chemistry and potential observational consequences.
How to cite: Braam, M., Hochman, A., Komacek, T., Sergeev, D., Yair, Y., Yaniv, R., Hills, M., and Mitchard, D.: Towards predicting lightning and TLE’s in exoplanetary atmospheres , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15529, https://doi.org/10.5194/egusphere-egu25-15529, 2025.
Lightning can indicate the location of strong convection in thunderstorms. We develop a lightning data assimilation observational operator based on a 2D-to-3D Bayesian method, which converts the 2D lightning distribution into vertical velocity profiles and RH profiles for each grid point in the plane. The new lightning observational operator provides a good representation of the shape and peak height of the instantaneous vertical velocity profiles in thunderstorms, rather than using a fixed or long-term averaged profile distribution. After 1-hour forecasting, experiments that assimilated both vertical velocity and water vapor still maintained a close vertical distribution to the observations in the lower layers. It also shows significant improvement in heavy rainfall forecasting within 1 hour, with a notable increase in precipitation scores. The improvement in heavy rainfall prediction primarily lies in the positive adjustment of the location of intense rainfall and the enhancement of rainfall intensity.
How to cite: Shaoxuan, D., Xiushu, Q., and Wei, H.: Lightning Assimilation based on a 2D-to-3D Bayesian method for Vertical Velocity and Water Vapor, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11142, https://doi.org/10.5194/egusphere-egu25-11142, 2025.
Lightning originates from electrical discharges driven by the non-inductive charging mechanism within thunderstorms. The charge separation in these regions is governed by the surrounding convective environment, storm dynamics, and microphysical processes, including updraft velocity and ice content, which intensify the storm's electric field. In recent decades, advances in understanding cloud microphysics, charge separation mechanisms, and thundercloud electrical structure have significantly improved lightning forecasting. The selection and tuning of parameterization schemes, particularly for microphysics (MP), cumulus (Cu), and lightning (LP) processes, play a critical role in enhancing model performance and accuracy.
This study uses various parameterization schemes to evaluate the performance of the Weather Research and Forecasting (WRF) model in simulating lightning and thunderstorm events. A severe thunderstorm event on May 14, 2022, over eastern India (West Bengal and Jharkhand), which recorded a peak 30-minute flash count of ~8000 flashes observed by the Indian Lightning Location Network (ILLN) was simulated in the WRF model. A total of 57 combinations of MP, Cu, and LP schemes were tested, using three nested domains (27 km, 9 km, 3 km) and analyzed the output of the inner domain (3 km). Seven MP schemes (WSM-6, Goddard, Thompson, Milbrandt, Morrison, WDM-5, WDM-6), two Cu schemes (Kain-Fritsch, Multi Kain-Fritsch), and two LP schemes (LP1: vertical velocity-based; LP2: 20 dBZ reflectivity-based) were assessed.
Results show better performance of LP2 over LP1 with higher correlation and lower standard deviation with the observed flash counts. For cumulus parameterization, Kain-Fritsch (KF) turned off for the inner domain, and achieved strong performance (correlation: 0.75–0.95) with lower RMSE and standard deviation. Among MP schemes, Morrison, Goddard, and WDM-6 consistently performed well across different combinations. The best-performing simulations included Goddard (LP2, KF on), Morrison (LP2, KF on), WDM-6 (LP2, KF off), and WDM-5 (LP2, KF on), achieving correlations of 0.94, 0.93, 0.91, and 0.91 with observed flash counts, respectively. This study underscores the WRF model's capability in simulating lightning activity with optimal parameterization combinations, particularly LP2 and KF schemes. These findings provide promising results for real-time lightning forecasting, aiding in mitigating lightning-related hazards.
How to cite: Rinuragavi, V., Biswasharma, R., Umakanth, N., and Pawar, S.: Evaluating Microphysics, Cumulus, and Lightning Parameterization Schemes in WRF Model for Thunderstorm Simulation Over East India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14876, https://doi.org/10.5194/egusphere-egu25-14876, 2025.
Dart leaders are a poorly understood lightning phenomenon where a current pulse propagates quickly (~10^7 m/s) along a previously established, now decayed, plasma channel, resulting in a re-heating of the channel. It is not understood how dart leaders propagate or how they get started. Therefore, in this work we have imaged the beginning of multiple dart leaders with the LOFAR radio telescope. We have observed two interesting phenomena related to the start of dart leaders. Firstly, we regularly observe other discharges, such as needles or `mini’ dart leaders, hundreds of microseconds before the start of the dart leader. The `mini’ dart leaders are particularly fascinating, as they propagate up side branches over a few hundred meters (towards the positive leader branch tip) before stopping. The main dart leader then initiates after the `mini’ dart leader. The exact connection between these preceding discharges (needles and mini-darts) and the main dart leaders, if one triggers the other, or why mini-darts ought to occur at all, are difficult to understand. In addition, previous work has shown that dart leaders tend to start with an exponential rise in VHF power and speed. In this work we find that some dart leaders have a period at their beginning where they propagate relatively slowly with weak VHF emission before a period of exponential growth. In one particular case, a dart leader initiated on a side branch, propagated slowly (~5x10^6 m/s) and weakly for about for about 100 µs until it connected with the main leader branch, and only then accelerated to a high speed (~ 1.7x10^7 m/s) over a period of about 50 µs. Finally, we will attempt to relate our measurements to recent hypothesis that dart leaders are a new kind of propagation that essentially amounts to a heating wave; the dart leader charge pushes a weak current in-front of it that heats up the plasma channel which in turn allows the current to increase further and the main charge packet to move forward.
How to cite: Hare, B., Scholten, O., Lourens, M., Turekova, P., Cummer, S., Dwyer, J., Liu, N., Pantuso, J., Da Silva, C., Sterpka, C., and ter Veen, S.: LOFAR Observations of Dart Leader Starts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8909, https://doi.org/10.5194/egusphere-egu25-8909, 2025.
M-components are transient enhancements of the channel luminosity occurring simultaneously with the continuing current phase of the cloud-to-ground lightning. They are initiated by the connection of the in-cloud channel to the grounded channel. We have developed a new model of M-component processes, which is based on the numerical solution of the Maxwell’s equations together with the Poisson’s equation for a given thundercloud charge structure. We compute the radiated electric and magnetic fields at various distances from the lightning channel. We model a microsecond-scale electric field pulse emitted during the connection of the in-cloud channel to the grounded channel and compare its waveform with measurements conducted in Florida. The modeled current waveforms at various heights above the ground are the outputs of our model and we compare them with measured luminosity curves. We also show how the M-component simulation results depend on the parameters of the model.
How to cite: Kaspar, P., Kolmasova, I., Marshall, T., Stolzenburg, M., and Santolik, O.: Electromagnetic model of M-components, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6249, https://doi.org/10.5194/egusphere-egu25-6249, 2025.
The study explores the characteristics of upward negative stepped leader pulses recorded at the Säntis Tower in Switzerland. Analysis of simultaneous channel-base current and 14.7-km vertical electric field data revealed two distinct types of pulses associated with upward negative stepped leaders [2].
Category A pulses were characterized by bipolar electric field signatures with initial positive half-cycles, correlated with negative unipolar current pulses. The E-field pulses had an average duration of 23.7 (± 11.7) μs and exhibited time-dependent characteristics, including increased frequency and slower risetimes.
Category B pulses were characterized by unipolar (positive or negative) or bipolar field signatures that lacked correlation with any major current pulses. These had narrower temporal widths compared to Category A pulses.
As discussed in Azadifar et al. 2018 [3], notable similarities exist between these two categories and, respectively, “Classical” and “Narrow” Preliminary Breakdown Pulses (PBPs) observed in the initial stages of downward negative leaders [6].
Herein, we present a statistical analysis of 45 Category A pulses from 5 Type-II upward positive flashes, which confirms their similarity to Classical PBPs, particularly in regards to key characteristic timescales reported in the literature, such as the aforementioned pulse duration [1,4,5,6,10], 10-90% risetime (6.1 ± 3.6 μs) [1,9], and zero-crossing time (11.9 ± 6.1 μs) [1,9]. In this dataset, 7 (~16%) of these bipolar pulses were observed to be inverted (with a negative initial half-cycle), and were excluded from this preliminary analysis, though it is of note that a similar phenomenon has been observed in downward stepped leaders as well [8].
The temporal widths of the initial and second half-cycles were observed to be linearly correlated (with correlation coefficient ρ = 0.77), as were their peak amplitudes (ρ = -0.80). Further linear correlations were found to exist between the peak E-field and current amplitudes (R2 = 0.74), as well as their risetimes (R2 = 0.73), with E-field pulses generally rising faster than current pulses. To the best of our knowledge, these specific relationships have not been reported in the literature, though correlations between PBP amplitude and: duration [7], and return stroke peak current [10] have been observed.
These findings enhance our understanding of upward lightning phenomena and associated electromagnetic radiation, revealing parallels with the Breakdown, Intermediate, and Leader stages of downward negative flashes. This study contributes to the ongoing debate about the underlying physical mechanisms of lightning initiation and propagation, and highlights the need for further research in this area. Observational studies are specifically recommended to validate these correlations and refine proposed modeling frameworks.
References:
[1] Adhikari & Adhikari (2021). Scientific World Journal, 2021, 1–9.
[2] Azadifar et al. (2015). XIII SIPDA, 32–36.
[3] Azadifar et al. (2018). 34th ICLP, 1–6.
[4] Cai et al. (2022). Atmospheric Research, 271, 106126.
[5] Granados et al. (2022). TecnoLógicas, 25(55), e2343.
[6] Nag & Rakov (2008). JGR: Atmospheres, 113(D1).
[7] Nag et al. (2009). Atmospheric Research, 91(2–4), 316–325.
[8] Ogawa (1993). Journal of Atmospheric Electricity, 13(2), 121–132.
[9] Shi et al. (2024). Remote Sensing, 16(20), 3899.
[10] Zhu et al. (2016). Atmosphere, 7(10), 130.
How to cite: Oregel-Chaumont, T., Azadifar, M., Šunjerga, A., Rubinstein, M., and Rachidi, F.: Comparing Upward Negative Stepped Leader and Preliminary Breakdown Pulses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18046, https://doi.org/10.5194/egusphere-egu25-18046, 2025.
The polarization of VHF radio signals emitted by lightning can help shed light on the intricate science of lighting propagation, through the direction of the corona VHF emission. However, this lightning radio polarization is not easily measured and, thus, understood. Employing the LOFAR radio telescope, we use a near-field beamforming algorithm (TRI-D) that coherently sums antenna voltages while accounting for the antenna function. This allows us to reconstruct VHF source location and polarization in 3 dimensions. In this work, we evaluate the accuracy of these unparalleled results. Performing a Monte Carlo error analysis, we simulate the antenna voltage signal resulting from a point-like dipole, which is then reconstructed with the imager. The difference between the input and the reconstructed source parameters gives us an approximation of the polarization error bars. We find that the polarization error is at maximum 12 degrees. This value fluctuates with varying source location and angle suspended between the polarization vector and the radial vector. We are testing the polarization reconstruction accuracy for radio point-like sources, background noise, and extended sources. We will present a comprehensive report on these results and their interpretation, our technique, and the imaging algorithm.
How to cite: Turekova, P., Hare, B., Scholten, O., Lourens, M., Cummer, S., Dwyer, J., Liu, N., Sterpka, C., and ter Veen, S.: LOFAR Lightning Data: Accuracy in Polarization Reconstruction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10850, https://doi.org/10.5194/egusphere-egu25-10850, 2025.
Convective weather, often associated with heavy precipitation, hail, lightning, and other hazardous phenomena, is highly unpredictable, short-lived, and localized, making forecasting and early warning particularly challenging. The formation of lightning is closely tied to the thermodynamic and microphysical processes within severe convective weather systems (e.g., Qie et al., 2021). Not only does it pose a significant threat to human life and properties, but it has also been recognized by the International Electrotechnical Commission (IEC) as a major hazard to power systems, communication networks, buildings, and electronic devices.
Since the mid-20th century, Doppler weather radars have been widely used to monitor hazardous weather by identifying precipitation, storm structures, and movement. Advances in radar technology, especially the introduction of array weather radar, have further enhanced the precision and timeliness of severe weather nowcasting. Unlike traditional single-antenna radars, array radars use multiple small antennas to form a large, flexible antenna array for rapid and precise beam control. This distributed phased-array system excels in detecting fine-scale flow and intensity fields, offering powerful tools for studying small-scale convective phenomena (e.g., Adachi et al., 2016).
This study utilizes array radar data from Foshan, Guangdong, China, high-precision lightning location data, and ground-based meteorological observation data to identify, track, and forecast severe convective weather. Based on a radar dual-threshold convective storm tracking and identification algorithm (e.g., Tian et al., 2019), combined with a lightning jump algorithm (e.g., Schultz et al., 2017), this nowcasting method monitors the lightning variation characteristics within strong convective cells (CCs), providing indices for severe convective weather. By comparing results with observations and optimizing algorithm parameters, the method improves hit rates, reduces false alarms, and achieves an average lead time of ~22 minutes with a hit rate over 80%, as demonstrated by case studies. This method can be effectively applied to enhance the monitoring and early warning capabilities for severe convective weather, thereby mitigating the impact of lightning and reducing lightning-related disasters for critical infrastructure, particularly power systems.
Acknowledgment
This work was jointly supported by the KERAUNIC project (ref: NIA2_NGET0055, National Grid Electricity Transmission, 2024) under the Network Innovation Allowance (NIA), the Arctic Pavilion Open Research Fund of Nanjing Joint Institute for Atmospheric Sciences under Grant BJG202410 and the China Scholarship Council program under Grant 202305330027.
References
Adachi, T., Kusunoki, K., Yoshida, S., et al. (2016). High-speed volumetric observation of a wet microburst using X-band phased array weather radar in Japan. Monthly Weather Review, 144(10), 3749-3765.
National Grid Electricity Transmission. (2024). Knowledge Elicitation of Risks to Assets Under LightNing Impulse Conditions (KERAUnIC). https://smarter.energynetworks.org/projects/nia2_nget0055
Qie, X., Yuan, S., Chen, Z., et al. (2021). Understanding the dynamical-microphysical-electrical processes associated with severe thunderstorms over the Beijing metropolitan region. Science China Earth Sciences, 64, 10-26.
Schultz, C. J., Carey, L. D., Schultz, E. V., & Blakeslee, R. J. (2017). Kinematic and microphysical significance of lightning jumps versus nonjump increases in total flash rate. Weather and forecasting, 32(1), 275-288.
Tian, Y., Qie, X., Sun, Y., et al. (2019). Total lightning signatures of thunderstorms and lightning jumps in hailfall nowcasting in the Beijing area. Atmospheric Research, 230, 104646.
How to cite: Xu, M., Qie, X., Tian, Y., Fullekrug, M., Gu, C., Bai, X., Ma, S., Liu, Y., Zhao, C., He, X., Li, B., Souto, L., Chikohora, T., and Dodds, D.: A Nowcasting Method for Severe Convective Weather Based on Array Radar and Lightning Jumps, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9498, https://doi.org/10.5194/egusphere-egu25-9498, 2025.
By combining space-based data from the Lightning Imaging Sensor (LIS) aboard the International Space Station (ISS) with broadband ground-based electromagnetic measurements, we investigate the relationship between electromagnetic emissions from lightning processes and their optical signatures, focusing on the lightning initiation phase. Our case study is based on data from the SLAVIA (Shielded Loop Antenna with Versatile Integrated Amplifier) magnetic detectors at various European locations, as well as on data from the lightning location systems ENTLN (Earth Networks Total Lightning Network), WWLLN (World Wide Lightning Location Network), EUCLID (European Cooperation for Lightning Detection), and from the SAETTA Lightning Mapping Array. Our analysis of 11 lightning flashes from 2020-2023 reveals that the light emitted during the preliminary breakdown stage can be clearly observable from the low Earth orbit, highlighting the potential for space-based systems to detect and study the lightning initiation processes.
How to cite: Kolínská, A., Kolmašová, I., and Santolík, O.: Space-Based Observations of Lightning Initiation: A Multisystem Case Study Combining Optical and Electromagnetic Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7073, https://doi.org/10.5194/egusphere-egu25-7073, 2025.
Thunderclouds and lightning produce high-energy radiation over a wide range of time scales. Terrestrial gamma-ray flashes (TGFs) are brief emissions lasting ~100 µs, consisting of photons with energies ranging from 20 keV to 40 MeV. Simultaneous ground-based measurements of electromagnetic fields and gamma-ray emissions have found TGFs to be associated with the evolutionary phases of both intracloud and cloud-to-ground lightning discharges.
Gamma-ray glows, on the other hand, last from a few seconds to several tens of minutes, typically coincide with the passage of thunderclouds, and are sometimes abruptly terminated by nearby lightning. Photons emitted during gamma-ray glows share the same energy spectrum as TGFs but are less intense. It was recently discovered that thundercloud regions can glow for hours and that gamma glows are more dynamic phenomena than originally thought.
Both types of gamma-ray emissions are believed to be generated via bremsstrahlung by energetic runaway electrons accelerated in the strong electric fields within thunderclouds. However, the connection between TGFs and gamma-ray glows remains not fully understood.
Until now, the only simultaneous gamma ray and radio wave measurements were conducted onboard an airplane during the ALOFT campaign. The TARANIS mission, which was intended to carry a unique set of electromagnetic, particle, gamma ray, and optical instruments, was unfortunately lost due to the failure of the Vega launcher in 2020.
The STRATELEC balloon project (part of the French-US STRATEOLE-2 project of long-duration balloon flights at the tropical tropopause), with precise synchronization of broadband electric field measurements and a gamma-ray detector, will provide a unique opportunity to correlate individual photon detections with electromagnetic pulses emitted by various lightning processes. These coordinated measurements could help answer the following questions:
- a) At which stage of the evolution of lightning discharges are TGFs produced?
- b) Which types of intracloud discharges produce detectable high-energy radiation?
- c) What are the differences in the electromagnetic signatures of lightning processes associated with TGFs and gamma glows?
- d) What are the temporal variations in electromagnetic emissions associated with gamma glows?
- e) Are flickering TGFs truly radio silent?
In this presentation, we introduce the FPGA-based radio receiver RIP (Radio Instrument Package), developed for the STRATELEC balloon project. The receiver is designed to capture and analyze the electromagnetic signatures of various lightning phenomena associated with gamma-ray production, including leader pulses, initial breakdown pulses, compact intracloud discharges, and dart-stepped leader pulses. The anticipated launch is late 2026.
How to cite: Kolmasova, I., Santolik, O., Celestin, S., Defer, E., and Lan, R.: Upcoming broadband electromagnetic balloon measurements related to terrestrial gamma ray flashes and gamma glows , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4072, https://doi.org/10.5194/egusphere-egu25-4072, 2025.
Terrestrial gamma-ray flashes (TGFs) are bursts of energetic X- and gamma-rays which are emitted from thunderstorms as the Bremsstrahlung radiation of relativistic electrons. Recently, the ALOFT (Airborne Lightning Observatory for FEGS and TGFs) mission has shown that the emission of such energetic radiation, also including gamma-ray glows and flickering gamma-ray flashes, is more abundant than previously thought. This raises the question how the relativistic electrons and photons interact with the atmosphere and whether they have an impact on the chemical composition while propagating through the atmosphere, potentially relevant for the production of greenhouse gases. The propagation and interaction of relativistic particles with the atmosphere can be studied with particle Monte Carlo collision models requiring cross sections as an input. Whilst there are well established data for photoionization, Compton scattering and pair production, we lack cross sections for photoexcitation, photodissociation or the excitation of air molecules through relativistic electrons which contribute to the chemical activation of the atmosphere. In order to fill this gap of data, we here present a novel numerical tool calculating cross sections for energetic particles propagating in air. We provide an overview of the code structure and present benchmarking cases against well-known cross sections. Additionally, we will present a first application by calculating cross sections for photodissociation for a wide range of energies. In the end, we will give an outlook how this will allow to pave the path for more realistic simulations of energetic phenomena in our atmosphere, relevant for chemical processes.
How to cite: Köhn, C. and van Gemert, H.: Towards the investigation of chemical effects of energetic electrons and photons in the atmosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1217, https://doi.org/10.5194/egusphere-egu25-1217, 2025.
TOTEM is a payload for observation of the fast processes of electrical activity at the top of thunderstorm clouds and for evaluation of a new camera technology with high time resolution and dynamic range, yet with low weight, data rate and power consumption. The Atmosphere-Space Interactions Module (ASIM) on the International Space Station (2018- ) discovered high levels of blue electrical corona activity in thunderstorm cloud tops reaching into the stratosphere. The discharges represent a new pathway of perturbations to greenhouse gas concentrations at high altitudes, which affect the atmosphere's radiative properties up to 5 times more than in the lower troposphere. However, the altitude of events and clouds are poorly resolved with the nadir-pointing instruments of ASIM. With instruments pointing at a slanted angle, TOTEM will measure the activity – and the cloud structure where they are found – with < 300 m altitude resolution to understand their regional and global impact on greenhouse gas concentrations. The instruments include neuromorphic cameras that allow image reconstruction at up to 100.000 frames per second. TOTEM is developed by an international network of scientists and engineers. It is studied under a contract with ESA. TOTEM can be implemented on the International Space Station (ISS) or other low-Earth Orbit platforms.
How to cite: Neubert, T., Chanrion, O., and J. Gordillo-Vazquez, F.: TOTEM: The Top of Thunderstorms Experimental Module, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21146, https://doi.org/10.5194/egusphere-egu25-21146, 2025.
While thunderstorm processes, such as the acceleration of electrons to relativistic energies, are widely studied, the computational challenges involved have made definitive proofs difficult to acquire. High precision in electric discharge simulations is achieved by resolving particles individually, via for example Monte Carlo methods, rather than by applying a fluid approximation; however, this is computationally expensive, and the multiscale nature of thunderstorm processes incurs additional difficulties. To address these challenges, we have developed the Atmospheric STReamer And Relativistic Particle Engine (ASTRAPÉ), a fully 3D GPU-based Monte Carlo particle-in-cell code capable of tracing approximately 109 computational particles, modeling all relevant electron-molecule collisions and solving the Poisson equation to include space charge effects. We will present the particulars of the GPU implementation, along with benchmarking against existing data and performance metrics. Additionally, we will discuss code optimization for LUMI (Large Unified Modern Infrastructure), Europe’s first pre-exascale supercomputer, which allows for exceptionally fast streamer simulations. Finally, we will discuss how ASTRAPÉ can be used to study the generation of relativistic electrons in thunderclouds.
How to cite: Fangel-Lloyd, E., Gourbin, P., Dujko, S., Gammelmark, M., Karlsson, S., Jara Jimenez, A. R., and Köhn, C.: ASTRAPÉ: Atmospheric STReamer And relativistic Particle Engine – a GPU-based particle code for pre-exascale supercomputing , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8563, https://doi.org/10.5194/egusphere-egu25-8563, 2025.
During the ALOFT flight campaign, July 2023, a novel type of multi-pulse gamma-ray emission from thunderclouds was systematically recorded. Referred to as flickering gamma-ray flashes (FGFs), this type of emission is not linked with lightning leaders and does not coincide with detectable radio emissions [1].
A promising candidate theory for explaining this phenomenon is the relativistic feedback discharge (RFD) developed by Dr. J. Dwyer and his group [2]. Fully self-consistent 3D Monte-Carlo calculations of RFD [3], which take the field quenching by produced currents into account, are quite computationally intensive. In fact, the full physics of RFD has barely been explored outside Dwyer’s group.
Therefore, we developed an independent numerical model especially made to evaluate the capability of the RFD theory to reproduce FGFs. Despite its simplification into a set of spatially-independent ordinary differential equations (ODEs), it applies the most relevant physics: ionisation, electron dynamics, attachment processes, relativistic runaway electron avalanche (RREA), and feedback akin to Dwyer’s theory. The ODEs that we end up solving are analogous to a complexified Lotka-Volterra model which describes a system with oscillations.
In this presentation, we introduce a 0.5D model (i.e., with indirect account of the spatial size of the RREA region) and demonstrate its ability to reproduce emission light curves very alike FGFs under realistic conditions, given the right set of parameters (see below). Furthermore, we show that the same model also reproduces light curves alike terrestrial gamma-ray flashes (TGFs, both single and multiple pulses) and gamma-ray glows (GRGs) for different sets of parameters but still under realistic conditions, hence proving this model to be even more general than originally intended.
With this, we performed a parameter-space exploration, using our model and systematically applying different values for 1) the initial (background) internal electric field strength of the cloud, 2) the characteristic growth time of the external electric field, 3) the vertical size of the high-field region in the cloud, and 4) the maximum change of the external field. The results, as shown in parameter-space diagrams, are qualitatively as expected. TGFs tend to occur for relatively small high-field regions. For larger high-field regions, the model reproduces GRGs in the case of slowly increasing external fields while FGFs and weak TGFs in the case of rapidly increasing external fields. The amplitude and the number of pulses typically scale with the maximum change of the external field. Finally, increasing the value of the initial internal electric field leads to a decrease in the minimum required change in the external field needed to reproduce FGFs, multi-pulse TGFs and GRGs.
References:
[1] Østgaard, N., Mezentsev, A., Marisaldi, M., Grove, J. E., Quick, M., Christian, H., Cummer, S., Pazos, M., Pu, Y., Stanley, M., et al., “Flickering gamma-ray flashes, the missing link between gamma glows and TGFs”, Nature (2023).
[2] Dwyer, J. R., “Relativistic breakdown in planetary atmospheres,” Physics of Plasmas, vol. 14, no. 4, p. 042901 (2007).
[3] Liu, N., Dwyer, D., “Modeling terrestrial gamma ray flashes produced by relativistic feedback discharges”, Journal of Geophysical Research (Space Physics), Vol. 118, no. 5, p. 2359-2376 (2013)
How to cite: Færder, Ø. H., Lehtinen, N., Sarria, D., Marisaldi, M., and Østgaard, N.: A parameter-space exploration of the Relativistic Discharge Model mapping for which conditions ALOFT’s Flickering Gamma-ray Flashes are produced, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10378, https://doi.org/10.5194/egusphere-egu25-10378, 2025.
Since the summer season of 2020, with the contributions from amateurs sited at different places mainly in the southern part of China, we have obtained the optical observations (most in colorful mode with relatively high image resolution) for nearly 1000 transient luminous events (TLEs). One of the major findings is that the coastal thunderstorms typically originating from somewhere in South China Sea could produce a burst of gigantic jets (GJs) during a special stage of its lifetime. We selected three thunderstorm cases of this situation and combine all available observational datasets (such as satellite brightness temperature, lightning detection, and radar reflectivity, etc.) to characterize the parent thunderstorms from several different perspectives. The general results regarding the features of thunderstorms in South China capable of producing GJs including a burst of overshooting thundercloud top penetrating the local tropopause, active lightning activity between the major charge regions, and also the elevated bottom of the thunderstorms. More detailed analyses regarding the genesis of GJ outbreak during a short time period of these thunderstorms are being implemented.
How to cite: Lu, G., Huang, H., and Zhao, Y.: Characterization of thunderstorms in South China that produced gigantic jets in a burst manner, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14901, https://doi.org/10.5194/egusphere-egu25-14901, 2025.
The CSES-01 satellite, with its versatile set of payloads, is able to detect short bursts of lightning-induced electron precipitation (LEP) simultaneously with injected up-going whistler waves. The electron bursts are identified individually for each telescope of the low-energy detector of the high-energy particle package (HEPP-L) within the energy range from 100 to 250 keV. The whistler wave detection is based on the power spectral density of the magnetic field in the frequency range from 1 to 10 kHz, measured by the search coil magnetometer (SCM). The wave and particle observations of CSES-01 are complemented by the ground-based lightning network of the World Wide Lightning Location Network (WWLLN). The found LEP events occur within ≤120 ms of the causative lightning discharge. A statistical study of the LEP events has been performed, which includes a background estimation for the wave-particle correlation. The identified LEP events are found to be shifted significantly polewards of the initial lightning and extend over some 1000 km longitudinally. In addition, it was found that the distance from the LEP event to the lightning decreases as the absolute lightning latitude increases. This finding is in agreement with models of electron interaction with obliquely propagating lightning-generated whistlers and observations from previous missions.
How to cite: Neubüser, C., Battiston, R., Burger, W. J., Follega, F. M., Papini, E., Perinelli, A., Piersanti, M., and Recchiuti, D.: A statistical study of lighting-induced electron precipitation (LEP) events observed by the CSES-01 satellite, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15696, https://doi.org/10.5194/egusphere-egu25-15696, 2025.
Recent aircraft campaign over the Caribbean region in July 2023, called ALOFT, resulted in several discoveries that significantly improved our understanding of atmospheric gamma-ray phenomena. It was demonstrated that strong convective systems produce strong, long lasting electric fields that generate highly dynamic gamma-ray glow emissions. About 600 individual glows, arranged in tens of glowing episodes were recorded, a certain part of which show abrupt decrease in photon flux due to some electrical discharge leading to reduction of the electric field in the active region. Many of those abruptly reset glows bear a bright terrestrial gamma-ray flash (TGF) at the very apex of the gamma-ray glow. All these TGFs are closely followed by a fast streamer discharge recorded as a positive narrow bipolar event (NBE) in radio and as a strong optical pulse in the 337 nm blue light emission with very little contribution in the 777.4 nm red light emission. This indicates that the +IC leader is not involved in this process, contrary to “conventional” leader-related TGFs usually observed from space. The partial discharge of the active volume and the gamma glow reset is achieved through the fast streamer discharge. The TGFs associated with this gamma glow reset process have very short rise time, short duration peak phase, and low fluence, which makes them undetectable from space and kept them undiscovered until the ALOFT campaign.
How to cite: Mezentsev, A., Østgaard, N., Marisaldi, M., Cummer, S., Pu, Y., Grove, E., Quick, M., Christian, H., Pazos, M., Stanley, M., Sarria, D., Lang, T., Schultz, C., and Blakeslee, R.: New Class of Gamma-Ray Flashes Indicate Gamma Glow Reset through Fast Streamer Discharge., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15838, https://doi.org/10.5194/egusphere-egu25-15838, 2025.
The influence of lightning on the atmospheric electric field (potential gradient, PG) is examined at Xanthi, NE Greece. The data span one year, 01/06/2011 - 31/05/2012. The influence of lightning distance on PG is large, and is evident up to distances of 50 km. At distances shorter than 1 km, the 1-min absolute PG values mean increase is 10 kV/m, while 1-sec values may increase above 20 kV/m for lightning distances below 10 km. It appears that PG increases linearly with decreasing lightning distance. Lightning can cause both positive and negative PG values. It is found that negative PG values increase faster than positive ones as the lightning distance decreases, and mean negative values are at any distance up to 50 km 20% higher than the mean positive ones. It is also examined how synoptic weather types influence lightning frequency and PG values. Circulation Weather Types (CWT) that produce more lightning near Xanthi are ones associated with high 500 hPa geopotential heights over the area and high thickness of the 850-500 hPa isobaric surfaces. Thgey are encountered predominantly during summer, and to a lower extend during spring and autumn. During such systems, when lightning was detected at distances shorter than 100 km from the site, the mean absolute values of PG were 1-1.2 kV/m.
How to cite: Kourtidis, K., Karagioras, A., Kosmadakis, I., and Kotroni, V.: On the influence of lightning distance on the atmospheric electric field, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1630, https://doi.org/10.5194/egusphere-egu25-1630, 2025.
An analysis of lightning strike statistics and spatial distributions in South Korea was conducted throughout 2023 to archive records and to support weather research through the use of radar data. The annual lightning strikes reached 73,341, demonstrating a twofold increase from 36,750 in the previous year but still below the 10-year (2014-2023) average of 93,380. Temporal analysis shows summer recorded the highest number of lightning strikes at 55,258, accounting for 75.35% of annual occurrences, a pattern consistent with the 10-year average. June, October, and December exhibited higher strikes than the 10-year average, while February, March, and August showed significantly lower activity. Spatial distribution examination identified Gyeongsangbuk-do as the dominant region with 12,892 strikes constituting 17.58% of the total. In contrast, Daejeon Metropolitan City recorded the lowest count with 270 strikes, equivalent to 0.37%. The grid investigation revealed high activity zones over the West Sea and around Seoul and Busan, representing increased strikes compared to the 10-year average. Ground-to-cloud discharges prevailed, with high intensities recorded over the South Sea relative to other regions. The five days with the highest number of lightning strikes were identified as 27 June, 11 July, 12 July, 26 July, and 26 October, followed by an analysis of regional strike distribution for each date. This study contributes to an improved understanding of lightning climatology in South Korea, enhancing meteorological forecasting capabilities.
This research was supported by the "Development of radar based severe weather monitoring technology (KMA2021-03121)" of "Development of integrated application technology for Korea weather radar" project funded by the Weather Radar Center, Korea Meteorological Administration.
How to cite: Ko, K., Chu, S., Nam, K.-Y., and Kim, K.-H.: Lightning statistics and spatial distribution in South Korea in 2023, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5416, https://doi.org/10.5194/egusphere-egu25-5416, 2025.
Lightning flashes with continuing current (CC) are a type of cloud-to-ground (CG) flash that pose significant risks, including air quality degradation, damage to electrical systems and the igniting of wildfires. Understanding CC lightning is important for mitigating its effects and assessing its potential connection to climate change.
In this study, we used a combination of space-based instruments (ASIM and GLM) and ground-based networks (ENTLN and ELF) to systematically identify CC lightning across the Contiguous United States (CONUS) from June 1, 2018, to December 31, 2021.
ASIM, aboard the International Space Station, provides high-resolution optical measurements at dual wavelengths (337.0 nm and 777.4 nm), while GLM offers continuous geostationary monitoring of optical emissions at 777 nm. Ground-based systems like ENTLN and ELF provide complementary radio data.
We utilized two distinct methods to classify lightning flashes as CC or no CC. The first relied on the predictive models of Fairman and Bitzer (2022), based on the optical signal of GLM, while the second utilized a metric derived from Extreme Low Frequency (ELF) magnetic signals.
We found clear differences between optical properties in ASIM dual-wavelength (337.0~nm, 777.4~nm) light curves associated with CC and no CC lightning, indicating potential for identifying CC flashes using ASIM optical recordings.
Results reveal optical and electromagnetic differences between CC and no CC lightning. First, CC flashes have longer-lasting optical emissions, higher power densities, and elevated total energy levels compared to no CC flashes. Second, the processed ELF radio signal can sense the presence of CC and the electrical polarity of lightning flashes. These findings highlight the value of combining space-based optical and ground-based ELF measurements to improve detection and classification of CC lightning.
How to cite: Camino-Faillace, P. A., Gordillo-Vazquez, F. J., Pérez-Invernón, F. J., Montanya, J., Mlynarczyk, J., Torsten, N., Chanrion, O., and Østgaard, N.: Characterizing continuing current lightning using multi instrument observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5624, https://doi.org/10.5194/egusphere-egu25-5624, 2025.
Central Africa is widely recognized as the most active region for thunderstorms globally, with the highest frequency of lightning strikes occurring near Kifuka in the Democratic Republic of Congo, where over 150 lightning flashes per square kilometer are recorded annually. The absence of accessible early warning systems in many developing countries significantly amplifies the risks associated with lightning. For instance, on August 28, 2020, a catastrophic lightning strike near the Uganda-Democratic Republic of Congo border resulted in the deaths of nine children, with a tenth succumbing while being transported to the hospital. Moreover, the detrimental effects of lightning on critical sectors—such as livestock, forestry, power utilities, aviation, high-tech industries, and public safety—are increasingly evident. A discernible rise in lightning-related fatalities has been observed, potentially attributable to population growth, which increases exposure to thunderstorms, or to changes in thunderstorm frequency driven by climate change. Regardless of the underlying causes, the risk posed to the African population remains significant and appears to be intensifying.
Building on the recent advancements of Denoising Diffusion Probabilistic Models (DDPMs)—which have demonstrated superior performance over adversarial and autoencoder-based frameworks in applications such as image generation, text-to-image synthesis, precipitation nowcasting, and weather forecasting—this research introduces an innovative nowcasting system. The proposed system predicts lightning probabilities up to six hours in advance, with 30-minute intervals, offering a probabilistic and life-saving early warning mechanism tailored for Central Africa.
Specifically, we investigate the potential of DDPMs for lightning nowcasting by adapting spatiotemporal frameworks originally developed for precipitation nowcasting. In essence, diffusion models learn the underlying data distribution Ρ(Χ), where Χ represents the spatiotemporal probability density function of lightning. This is achieved by training the model to reverse a predefined noising process that progressively corrupts the target data with Gaussian noise. Here, the diffusion process has been extended to condition on auxiliary data Υ, such as satellite-derived wavelength imagery, constituting the approach suitable for spatiotemporal conditional nowcasting Ρ(ΧΥ).
As a data source, we leverage recent datasets from the Meteosat Third Generation (MTG) Lightning Imager (LI) over Africa and the Earth Networks Total Lightning Network (ENTLN) to train the model that locally characterizes the stochastic nature of lightning events.
How to cite: Landa, V., Price, C., and Reuveni, Y.: Nowcasting Thunderstorms to Protect Lives in Africa, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9121, https://doi.org/10.5194/egusphere-egu25-9121, 2025.
This study investigates the phenomenon of “Superbolts”, High-intensity lightning flashes – by examining their occurrence and correlations across multiple lightning monitoring networks. Given inconsistencies in Superbolt definitions in prior research, this study addresses the feasibility of establishing a universal definition for Superbolts and analyzes the inherent challenges to do so.
A statistical methodology was used to study Superbolts occurrence across three datasets: the ISS Lightning Imaging Sensor (LIS), the World-Wide Lightning Localization Network (WWLLN), and the Earth Networks Total Lightning Networks (ENTLN). This study employed current peak power and energy thresholds to propose statistical-based thresholds for Superbolts radiance and used spatial and temporal matching criteria to examine the correlation between the occurrence of Superbolts in different detection methods.
This study identified notable divergences between spatial and temporal distributions of Superbolts across different systems. Both LIS and WWLLN datasets show high-density regions of superbolts over the Maritime Continent of Asia, South America, and South Africa, but disparities appear around Australia, Central America, and northern regions. Moreover, temporal analysis shows a seasonal dependency, with LIS data indicating higher Superbolt incidence in summer, contrasting with WWLLN's peak during winter. While WWLLN data partially align with Kirkland's "three Superbolt chimneys" (1999), the observed high-density regions differ substantially from those presented in Holzworth et al. (2019). Correlation analysis between ENTLN and LIS datasets showed insignificant matching in Superbolts occurrence.
These findings underscore the inherent challenges to establish a universal definition for Superbolts, especially when comparing data from optical-based and RF-based monitoring networks. Challenges include differences in temporal and spatial coverage, detection biases due to atmospheric conditions, and non-unique matching of flashes. Hence, system-specific or statistical based thresholds may provide a more feasible alternative. Future research should include meteorological data, such as clouds cover and optical-depth, and explore the relationships between global lightning distribution and Superbolts formation.
How to cite: Yehieli, N., Price, C., and Yair, Y.: Comparing lightning Superbolts detected independently in the optical and VLF ranges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12365, https://doi.org/10.5194/egusphere-egu25-12365, 2025.
Lightning is a significant disturbance agent in tropical forests, with ecological impacts including tree mortality and influencing forest structure and carbon dynamics. Our research explores the environmental and tree-specific factors affecting the probability of a tree being struck by lightning in Afromontane forests. We surveyed 89 kilometers of transects across ridges, slopes, and valleys in Bwindi Impenetrable National Park, Uganda, and recorded 94 lightning strikes.
Our findings reveal that topography significantly influences strike probability, with ridges experiencing the highest strike density (2.0 strikes/km) compared to slopes (1.4 strikes/km) and valleys (0.25 strikes/km). Elevation alone was not a significant predictor when topography was included, suggesting that a tree's relative position in the landscape plays a crucial role.
At the individual tree level, struck trees were not always the tallest within a 20-meter radius plot. Only 30% of struck trees had the largest diameter at breast height (DBH), and 19.5% were the tallest, highlighting the influence of factors beyond size. However, struck trees exhibited a higher median DBH and a greater proportion of emergent canopy trees compared to controls. Generalized Linear Mixed Models (GLMM) identified DBH (Estimate = 0.025, p < 2.39e-06) and canopy exposure (Estimate = 1.20, p = 2.04e-08) as significant predictors of strike probability.
These results suggest that lightning strikes are influenced by a combination of environmental and tree-specific traits, including topographical context, DBH, and canopy exposure. Our findings contribute to understanding lightning as a selective agent in tropical forests, with implications for forest dynamics and carbon storage.
How to cite: Zoletto, B., Van der Sande, M., Van der Sleen, P., Babaasa, D., Nkwasibwe, A., Gora, E., Sullivan, M., and Cuni-Sanchez, A.: Tree and Forest Traits Influencing Lightning Strike Probability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17913, https://doi.org/10.5194/egusphere-egu25-17913, 2025.
How to cite: Lourens, M., Hare, B., Scholten, O., Turekova, P., Cummer, S., Dwyer, J., Liu, N., Sterpka, C., and ter Veen, S.: High resolution imaging of negative leader propagation with LOFAR, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11832, https://doi.org/10.5194/egusphere-egu25-11832, 2025.
How to cite: Bentley, M., Sae-jung, J.-J., Duan, Z., and Gerken, T.: Thermodynamic-Aerosol Relationships of Thunderstorm Environments in the Bangkok Metropolitan Region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13218, https://doi.org/10.5194/egusphere-egu25-13218, 2025.
In July 2023, the ALOFT flight campaign deployed an ER-2 research aircraft that flew at 20 km altitude above thunderstorms, carrying an extensive suite of instruments. The campaign observed numerous gamma-ray glows exhibiting complex and highly dynamic morphologies (Marisaldi et al. 2024). This study focuses on two specific glow events recorded on July 29th, 2023, between 20:30:20 and 20:31:40 UTC over Florida. By combining Monte Carlo simulations with observations from hard-radiation instruments and ground-based interferometers, we can estimate the multiplication factor required, based on cosmic-ray secondary electrons, to produce gamma-ray glows of the observed magnitude (exceeding 7 times the background level on the ALOFT-BGO detector).
Our analysis reveals multiplication factors of seed electrons (cosmic-ray secondaries) significantly exceeding a factor 5000, occurring multiple times and persisting for periods of several seconds. According to previous studies (Dwyer et al. 2007; Kelley et al. 2015), such high multiplication factors indicate substantial contribution from the Relativistic Feedback Discharge mechanism. Using the methodology established by Kelley et al. (2015), we estimated that the discharge currents resulting from the relativistic process during high-intensity phases of the glow could range in the tens to hundreds of amperes. These values substantially exceed those previously reported by Kelley et al. (2015) and could be large enough to significantly influence the thunderstorm's charging rate.
This study provides evidence that the Relativistic Runaway Electron Avalanche process, amplified by the relativistic feedback mechanism, could compete with conventional discharge mechanisms in certain thunderstorm conditions.
References:
- Marisaldi, M., Østgaard, N., Mezentsev, A., Lang, T., Grove, J. E., Shy, D., Heymsfield, G. M., Krehbiel, P., Thomas, R. J., Stanley, M., Sarria, D., Schultz, C., Blakeslee, R., Quick, M. G., Christian, H., Adams, I., Kroodsma, R., Lehtinen, N., Ullaland, K., Yang, S., Qureshi, B. H., Søndergaard, J., Husa, B., Walker, D., et al. (2024). Highly dynamic gamma-ray emissions are common in tropical thunderclouds. Nature. https://doi.org/10.1038/s41586-024-07936-6
- Kelley, N. A., Smith, D. M., Dwyer, J. R., Splitt, M., Lazarus, S., Martinez-McKinney, F., Hazelton, B., Grefenstette, B., Lowell, A., & Rassoul, H. K. (2015). Relativistic electron avalanches as a thunderstorm discharge competing with lightning. Nature Communications. https://doi.org/10.1038/ncomms8845
- Dwyer, J. R. (2007). Relativistic breakdown in planetary atmospheres. Physics of Plasmas. https://doi.org/10.1063/1.2709652
How to cite: Sarria, D., Østgaard, N., Marisaldi, M., Mezentsev, A., Lehtinen, N., Bjørge-Engeland, I., Fuglestad, A., Lang, T. J., and Stanley, M. A. and the The ALOFT Team: Evidence of gamma-ray glows observed in the relativistic feedback regime during the ALOFT 2023 flight campaign, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16240, https://doi.org/10.5194/egusphere-egu25-16240, 2025.
Lightning initiation is one of the top unsolved problems in atmospheric electricity. Runaway electron breakdown of air has been suggested to play a key role in lightning initiation, by locally enhancing the ambient electric field above the conventional breakdown threshold. The recent results from the ALOFT flight campaign have shown a tight interconnection between highly convective cores, lightning activity, and high-energy particle acceleration observed as a wide range of gamma-ray phenomena (gamma-ray glows, Terrestrial Gamma-ray Flashes, and the recently reported Flickering Gamma-ray Flashes). Thanks to the combination of simultaneous, high-sensitivity gamma-ray, optical and radio measurements, the ALOFT dataset provides a unique opportunity to investigate the lightning initiation problem and test the runaway breakdown hypothesis. Here we focus on the lightning discharges observed within the field of view of the gamma-ray instrument and not associated to any detectable gamma-ray enhancement. We will try to answer the following questions: how many discharges are there unambiguously not associated to gamma-rays? What are the characteristics of these discharges? What can we infer about the hypothesis of lightning initiation triggered by runaway air breakdown?
How to cite: Marisaldi, M., Østgaard, N., Mezentsev, A., Sarria, D., Lehtinen, N., Bjørge-Engeland, I., Fuglestad, A., Færder, Ø., Lang, T. J., Quick, M., Blakeslee, R., Christian, H., Grove, J. E., Shy, D., Cummer, S. A., Pu, Y., and Pazos, M.: Testing the hypothesis of lightning initiation by runaway air breakdown with ALOFT data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18036, https://doi.org/10.5194/egusphere-egu25-18036, 2025.
About 45 lightning flashes occur per second all around the Earth with a predominant distribution over the continents and along the inter-tropical band. While different types of Transient Luminous Events (TLEs) induced by lightning flashes can be produced above the thunderstorms, Terrestrial Gamma Ray Flashes (TGFs) are bursts of high-energy photons originating from the Earth’s atmosphere in association with thunderstorm activity with a great majority of TGFs occurring in the inter-tropical region. In addition to those radiation bursts, another type of high-energy emission, so-called gamma ray glows, has been observed inside thunderstorms corresponding to significant enhancements of background radiation that last for more than a few seconds. All these connected phenomena remain to be documented both remotely and on an in-situ manner. Balloon-borne missions offer the required in-situ close-range high-altitude measurements of the ambient electrostatic field, conductivity, TGF radiation and lightning occurrence for a better understanding and modeling of these complex phenomena and of their effects on the Earth atmosphere and the global atmospheric electrical circuit.
The STRATELEC (STRatéole-2 ATmospheric ELECtricity) project (Defer et al., 2022), funded by CNES, aims at deploying within the Stratéole-2 framework (Hertzog and Plougonven, 2020) new atmospheric electricity instrumentation on several stratospheric balloons to:
- Document the electrical state of the atmosphere and the production of high-energy radiation through in-situ and remote sensing measurements to reach better understanding and better modeling capabilities of the processes occurring during thunderstorms,
- Identify state-of-the-art and emerging technologies to populate the STRATELEC instrumentation package with new sensors in the perspective of their operation on stratospheric balloons, high altitude aircraft and even low-level drones to eventually propose new balloon and/or space mission concepts,
- Contribute to additional scientific returns on any space mission dedicated to lightning detection (e.g. MTG-LI, GOES-GLM) and more generally to the study of the convection in the Tropics and of electrodynamic couplings in the terrestrial atmosphere-ionosphere-magnetosphere system.
First, we will remind the scientific objectives of the STRATELEC project. Then we will provide an update on the different scientific and technical activities, including the development and the testing of STRATELEC instruments, but also the data analysis méthodology. Finally, we will discuss the way forward for the upcoming and final Stratéole-2 campaign (winter 2026-2027), as well as some initial thoughts on future balloon campaigns.
Hertzog A., and R. Plougonven (2020), Stratéole-2 : des ballons longue durée pour étudier la tropopause tropicale, La Météorologie - n° 108 - février 2020.
Defer, E., et al. (2022), An Overview of the STRATELEC (STRatéole-2 ATmospheric ELECtricity) Project, 25th ESA Symposium on European Rocket and Balloon Programmes and Related Research, 1-5 May 2022, Biarritz, France.
How to cite: Defer, E., Soula, S., Célestin, S., Hazem, Y., Trompier, F., Kolmašová, I., Santolík, O., Lán, R., Berthelier, J.-J., Seran, E., Godefroy, M., Hertzog, A., and Venel, S.: The STRATELEC (STRatéole-2 ATmospheric ELECtricity) project, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4814, https://doi.org/10.5194/egusphere-egu25-4814, 2025.
Several successful attempts have been made so far to utilize the uninterrupted view on the atmosphere from space and discover yet undocumented features of lightning activity and transient luminous events (TLEs), most recently THOR and ILAN-ES (2022-2024). As Hungary is considering sending an astronaut to the International Space Station (ISS) in 2025, an experiment has been proposed that aims at further enriching the existing set of space-borne targeted observations of nighttime electrical phenomena in the atmosphere. This is to be accomplished by an optical camera which is directed to preselected thunderstorm targets by the astronaut. This would be the UHU experiment which has been named after the Eurasian eagle-owl, a nighttime predator bird known for its extremely silent flight and exceptionally sharp eyes. The experiment is planned to be supported by a ground-based global observation and data collection campaign. One utterly desired achievement of the experiment and the accompanying observation campaign would be obtaining optical records of one or more TLEs taken simultaneously from the ISS and from a ground location. The experiment would also serve to elevate public awareness about the benefits of monitoring atmospheric electric parameters in studying the atmosphere and the near-Earth space environment. In this contribution, the motivation and the scientific aims behind organizing yet another TLE observation experiment from the ISS are presented and planning of the experiment as well as the supporting observation campaign are described.
How to cite: Bór, J., Yair, Y., Hegedüs, T., and Jäger, Z.: UHU - another experiment to observe lightning and TLEs from the ISS, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5994, https://doi.org/10.5194/egusphere-egu25-5994, 2025.
For over two decades, optical observations from low Earth orbit satellites have enabled the creation of the first global map of lightning activity. Today, the latest generation of geostationary meteorological satellites, such as the European Meteosat Third Generation (MTG) Lightning Imager (LI), is equipped with lightning imagers. Additionally, instruments like the Lightning Imaging Sensor (LIS) and the Atmosphere-Space Interactions Monitor (ASIM) on board the International Space Station detect optical lightning signals across various wavelengths, ranging from near-UV to near-IR, with cameras and photometers.
Understanding the radiative transfer of light generated by lightning discharges within clouds is crucial for interpreting detected optical signals. In this work, the three-dimensional radiative transfer code 3DMCPOL (Cornet et al., 2010) is adapted to simulate realistic lightning waveforms and images. The 3DMCPOL code simulates light propagation through three-dimensional atmospheres using the Monte Carlo method, originally for solar or thermal sources. A realistic four-dimensional (time and space) lightning source was implemented (Rimboud et al., 2024), and its detection by ground-based or space-borne photometers and cameras.
The methodology will first be detailed, focusing on how realistic imagery observations are simulated using geometric models of the Lightning Optical Imager (LOI) developed by the French space agency for the French-Israeli C³IEL (Cluster for Cloud Evolution, Climate, and Lightning) mission currently under development. Then, simulations of realistic daytime LOI observations will be presented using the microphysical outputs of the French cloud-resolving model Meso-NH for the cloud description. First results on the necessary acquisition frequency for background scenes and the impact of tilted observations on lightning detection, will be discussed from these simulations.
How to cite: Rimboud, A., Defer, E., Cornet, C., Thieuleux, F., and Ricard, D.: First Simulations of Lighthing Optical Observations during Daytime in the Context of the C³IEL Mission, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19743, https://doi.org/10.5194/egusphere-egu25-19743, 2025.
The Tibetan Plateau stands as the highest plateau globally, showcasing distinct geological and climatic characteristics. Thunderstorms there usually shows unique structural and spatiotemporal features compared to those in low-altitude plains, and they typically exhibited small size, short duration, lower charging and flash rate. Using the data from the accurate lightning VHF interferometer, electric field mill, fast/slow antenna and C-band radar, evolution of charge structure of thunderstorms involved in lightning discharge are investigated. Different from the lower-altitude thunderstorm usually starting from a positive dipole charge structure in the middle upper portion of cloud, the charge structure inside thunderstorm usually evolves from an initial inverted dipole charge structure. In the mature stage, it may keep the inverted dipole in the whole life cycle of the thunderstorm, or exhibit a bottom heavy tripole charge structure with a large lower positive charge center (LPCC). Under different magnitudes of the LPCC, various lightning discharges including -IC, +IC, -CG and bolt-from-blue flashes are generated, indicating the crucial effects of LPCC on the lightning discharge types.
How to cite: Qie, X., Liu, D., Li, F., Sun, Z., Yuan, S., and Jiang, R.: Bottom-dominated negative dipole charge structure in thunderstorms over Tibetan Plateau , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21157, https://doi.org/10.5194/egusphere-egu25-21157, 2025.
The Lightning Mapping Imager (LMI) onboard the Fengyun-4A (FY-4A) satellite is the first independently developed satellite-borne lightning imager in China. It enables continuous lightning detection in China and surrounding areas, regardless of weather conditions. The FY-4A LMI uses a Charge-Coupled Device (CCD) array for lightning detection, and the accuracy of lightning positioning is influenced by cloud top height (CTH). In this study, we proposed an ellipsoid CTH parallax correction (ECPC) model for lightning positioning applicable to FY-4A LMI. The model utilizes CTH data from the Advanced Geosynchronous Radiation Imager (AGRI) on FY-4A to correct the light-ning positioning data. According to the model, when the CTH is 12 km, the maximum deviation in lightning positioning caused by CTH in Beijing is approximately 0.1177° in the east–west direction and 0.0530° in the north–south direction, corresponding to a horizontal deviation of 13.1558 km, which exceeds the size of a single ground detection unit of the geostationary satellite lightning imager. Therefore, it is necessary to be corrected. A comparison with data from the Beijing Broadband Lightning Network (BLNET) and radar data shows that the corrected LMI data exhibit spatial distribution that is closer to the simultaneous BLNET lightning positioning data. The coordinate differences between the two datasets are significantly reduced, indicating higher consistency with radar data. The correction algorithm decreases the LMI lightning location deviation caused by CTH, thereby improving the accuracy and reliability of satellite lightning positioning data. The proposed ECPC model can be used for the real-time correction of lightning data when CTH is obtained at the same time, and it can be also used for the post-correction of space-based lightning detection with other cloud top height data.
How to cite: Zhang, Y., Qie, X., Cao, D., Yang, J., and Wang, D.: Correction of Parallax Shift Effect Based on Cloud Top Height for FY-4A LMI, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4688, https://doi.org/10.5194/egusphere-egu25-4688, 2025.
During the Airborne Lightning Observatory for FEGS and TGFs (ALOFT) campaign conducted in the summer of 2023, hundreds of gamma-ray glows were observed. Numerous glow regions, each consisting of several individual glows, were observed as the aircraft passed over active thunderstorms (Marisaldi et al. 2024). We will investigate the mechanisms behind the termination of the individual glows, focusing on whether specific types of discharges are responsible or if the glows terminate themselves. We will combine observations from different instruments onboard the aircraft, including gamma-ray detectors, electric field change meters and photometers. Lightning discharges will be characterized by optical emissions and data from on-board electric field change meters. We also couple this with detections by the ground-based lightning location network GLD360.
References:
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Marisaldi, M., Østgaard, N., Mezentsev, A., Lang, T., Grove, J. E., Shy, D., Heymsfield, G. M., Krehbiel, P., Thomas, R. J., Stanley, M., Sarria, D., Schultz, C., Blakeslee, R., Quick, M. G., Christian, H., Adams, I., Kroodsma, R., Lehtinen, N., Ullaland, K., Yang, S., Qureshi, B. H., Søndergaard, J., Husa, B., Walker, D., et al. (2024). Highly dynamic gamma-ray emissions are common in tropical thunderclouds. Nature. https://doi.org/10.1038/s41586-024-07936-6
How to cite: Bjørge-Engeland, I., Østgaard, N., Marisaldi, M., Mezentsev, A., Fuglestad, A. N., Sarria, D., Lehtinen, N., Lang, T. J., Schultz, C., Christian, H., and Quick, M. G.: Investigating the termination mechanisms of gamma-ray glows observed during the ALOFT aircraft campaign, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16451, https://doi.org/10.5194/egusphere-egu25-16451, 2025.
Electric fields in thunderclouds can accelerate electrons to relativistic energies, which leads to bremsstrahlung production of gamma radiation. This radiation was recently recorded by the ALOFT experimental aircraft campaign [1], and may be classified into various types according to their lightcurve shapes, for example, flickering gamma flashes (FGF), single and multiple terrestrial gamma flashes (TGF), and extended gamma-ray glows (GRG). Electromagnetic field in radio and optical range was also recorded, and has different features for the enumerated gamma radiation types.
The relativistic runaway electrons may be produced in various ways. We consider two different mechanisms: (1) electrons are accelerated from low energies in high fields at the tips of long streamers, and (2) runaway electrons grow in large-scale (km-size) avalanches sustained by relativistic feedback mechanism [2].
The first mechanism (long streamers) is analyzed using the novel Streamer Parameter Model (SPM) [3]. This model had been shown to agree with experiments for laboratory-size streamers, and here it is applied to streamers exceeding several meters in length. Such long streamers may describe the fast positive and negative breakdown (FPB/FNB), experimentally observed in thunderstorms. The long streamers, compared to regular laboratory-observed streamer, are predicted to have higher (subluminal) velocities, higher electric fields at the tip, and wider tips. These factors all facilitate production of large quantities of relativistic runaway electrons and, therefore, efficient radiation of x-rays in the form of short pulses, which may be observed as TGF. The currents radiate a short electromagnetic pulse similar to the observed narrow bipolar events (NBE).
The second mechanism (large-scale feedback) is analyzed using the recently developed 0.5D FGF model [4] which is a dynamic model of electric field and cloud conductivity connected through production of relativistic runaway electrons, secondary electrons and ions. This model describes a system in which oscillations may be excited by changing external field [2]. For various set of parameters (such as the system size, and time scale and strength of the external field change), as analyzed by [4], one may obtain gamma radiation lightcurves similar to all the observed types listed above. Charge redistributions and electric currents, for certain sets of parameters, may produce detectable electromagnetic fields.
For both mechanisms, we also calculate optical radiation excited by secondary electrons and estimate its detectability.
[1] N. Østgaard et al, Flickering gamma-ray flashes, the missing link between gamma glows and TGFs. Nature, 634, p. 53-56, 2024. doi:10.1038/s41586-024-07893-0.
[2] N. Liu and J. R. Dwyer. Modeling terrestrial gamma ray flashes produced by relativistic feedback discharges. J. Geophys. Res.–Space, 118 (5), p. 2359-2376, 2013. doi:10.1002/jgra.50232.
[3] N. G. Lehtinen (2021). Physics and Mathematics of Electric Streamers, Radiophys Quantum El, 64, p. 11-25, doi:10.1007/s11141-021-10108-5.
[4] Færder et al, this session.
How to cite: Lehtinen, N., Færder, Ø. H., Sarria, D., Mezentsev, A., Marisaldi, M., and Østgaard, N.: Optical and radio emissions from different high-energy electron acceleration mechanisms, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16145, https://doi.org/10.5194/egusphere-egu25-16145, 2025.
Atmosphere Space Interaction Monitor (ASIM) has been in operation since 2018 to observe Terrestrial Gamma-ray flashes (TGFs) and optical signals from lightning. ASIM has two payloads, the Modular X- and Gamma-ray Sensor (MXGS) and the Modular Multi-Spectral Imaging Assembly (MMIA). MXGS consists of two detector layers, one pixelated detector in the low energy range (50 keV to 400 keV) and another in the high energy range (300 keV to >30 MeV), with temporal resolution of 1µs and 28 ns, respectively. MMIA has three photometers (337 nm, 180-230 nm, 777 nm) and two cameras (337 nm and 777 nm). During nighttime we observe both the TGFs and the lightning that produced them.
Multiple and double TGFs separated by 1-2 ms have frequently been observed by ASIM. Here we present double TGFs, which were all associated with optical pulses from a hot leader (777 nm). Furthermore the first and second pulses come from the same location, indicating that the double TGFs are produced by the same leader as it propagates upward.
A related but different gamma-ray phenomenon was observed during the ALOFT campaign in 2023, when more than 25 Flickering Gamma.ray Flashes were observed. The FGFs are trains of pulsed gamma-ray emissions, each pulse lasting typically 1-2 ms and the entire FGF last about 50-100 ms. The FGFs have no associated detectable optical or radio signal, which differentiate them from the multi-TGFs. The FGFs observed during the ALOFT campaign were all too weak to be seen from space.
However, in May 2024 ASIM passed over pulsed gamma-ray emissions which was identical to the FGFs seen by ALOFT, but contrary to the ones observed by ALOFT, this FGF was bright enough to be seen from space.
Unfortunately, the FGF occurred during day-time over the coast of West Africa, so no optical data were available - and radio coverage is also very poor in this region.
How to cite: Ostgaard, N., Fuglestad, A., Mezentsev, A., Marisaldi, M., Sarria, D., Neubert, T., Chanrion, O., Christiansen, F., Gordillo-Vazques, F., and Luque, A.: The difference between multiple TGFs and FGFs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15628, https://doi.org/10.5194/egusphere-egu25-15628, 2025.
