This session seeks contributions from research in atmospheric electricity with emphasis on:
Atmospheric electricity in fair weather and the global electrical circuit
Effects of dust and volcanic ash on atmospheric electricity
Thunderstorm dynamics and microphysics
Middle atmospheric Transient Luminous Events
Energetic radiation from thunderstorms and lightning
Experimental investigations of lightning discharge physics processes
Remote sensing of lightning and related phenomena by space-based sensors
Thunderstorms, flash floods, tropical storms and severe weather
Lightning-ignited wildfires and ecological effects of lightning
Connections between lightning, climate and atmospheric chemistry
Modeling of thunderstorms and lightning
Now-casting and forecasting of thunderstorms using machine learning and AI
Regional and global lightning detection networks
Lightning Safety and its societal effects
Planetary lightning in the solar system and beyond
Intense lightnings and hailfall are both hallmarks of severe convective storms, but they are rarely associated with long-term climate studies. The main reason is the lack of long-term observations. But recently, the term “extreme weather” is often cited in media as a possible dire consequence of worsening global warming in the foreseeable future, however, it is often ambiguous of what type of extreme weather they are referring to. Most recent future predictions are done by performing climate model simulations under certain global warming scenarios. However, the resolution of the current generation climate models is not good enough to resolve individual storm system let alone pinning down the physical mechanisms. This ambiguity in physical mechanism impedes the better understanding of the nature of these extreme weather/climate events. In this paper, we present a unique study to show that severe storms with intense lightnings and hailfall are indeed connected with long-term climate change.
In this study, we utilize the meteorological series derived from the REACHES climate database compiled from Chinese historical documents (Wang et al., 2018; 2024, Nature: Scientific Data) and extract temperature, lightning and hailfall times series for the period of 1368-1911 (a 543-year period) and performed correlation analysis among them. Our results show that there exists strong negative correlation between either temperature-lightning or temperature-hailfall pair. This means that severe convective storms as manifested by intense lightning and heavy hailfall occurred in colder climate periods. The correlation coefficients for both pairs are close to -0.9 for the 30-year moving average series. Such a stable correlation over such a long period indicates that this cannot be a random coincidence but there must be persistent physical mechanisms involved. The temperature-lightning correlation is stronger, indicating that the climate physical state must be closely connected with atmospheric electricity.
We have made further analyses by looking into different seasons to understand the seasonal variations of the above negative correlation. We will also investigate the regional variations of the above relation. These results will shed more lights to the physical mechanisms responsible for this phenomenon. We will also utilize physics-based storm model simulation results to understand the possible dynamical processes involved.
How to cite: Wang, P. K.: A long-term atmospheric electricity-climate connection study using a 543-year long historical data set, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18253, https://doi.org/10.5194/egusphere-egu26-18253, 2026.
In recent years, our knowledge of turbulence statistics inside cumulus, stratiform, and stratocumulus clouds is more complete thanks to a number of measurement campaigns and subsequent detailed analyses of collected data. However, similar cannot be stated for cumulonimbus clouds. This is primarily because very few measurements have been performed, majorly owing to safety issues amidst harsh atmospheric conditions. At the same time, even though the extent of electrification is present in all kinds of clouds, cumulonimbus clouds are particularly significant because of the final result of electrification, in the form of lightning. Thus the necessity to understand the evolution of electric field in such conditions is highly crucial. In this study, we use data from the campaign, Severe Thunderstorm Electrification and Precipitation Study (STEPS), performed in the May of 2000 in Kansas, USA. The campaign consisted of aircraft penetrations into the mature thunderstorm cloud and several balloon soundings. This involved in-situ measurements of electric field, vertical velocity, liquid water content, etc.
Charges inside the clouds are under constant motion, owing to convective motions such as updraft and downdraft. This causes them to be scattered around in various regions of the clouds and form clusters depending on how turbulent these regions are. In our study, we compared the evolution of turbulence and electric field inside the clouds. Our results show negative correlation between the turbulent kinetic energy dissipation rates and modules of the electric field vector, which suggests the growth of electric field in regions of weak turbulence and vice versa. This could mean that larger charges exists in those regions where turbulence is on the verge of decay or it is in the process of development. Vice versa, the presence of strong turbulence destroys the charges clusters. We also investigate the intermittency, which is a notable indicator for turbulent fields. Specifically, we calculated the probability density functions of electric field differences at two points. For small differences those functions are clearly non-Gaussian, with long stretched tails and conical tip, which is a very typical picture for intermittency. For larger lags, the distributions are closer to gaussian, thereby signifying a homogenous arrangement of charges.
How to cite: Sarkar, J., Wacławczyk, M., and Malinowski, S.: Study of electric fields and turbulence in thunderstorm clouds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7491, https://doi.org/10.5194/egusphere-egu26-7491, 2026.
How lightning initiates in thunderstorm fields well below the conventional breakdown electric field Ek, which is defined by the equality of the ionization and dissociative attachment coefficients in air [Raizer, 81 1991, p. 135], remains an outstanding question. We investigate a robust pathway for streamer ignition through the collision of charged hydrometeors. By extending a two-particle image-charge model [Cai et al., 2018, https://doi.org/10.1029/2018JD028407] to include an initial charge Q, we quantify how polarization, particle dimensions, and background fields control ignition thresholds. We identify a "diagonal valley" of optimal radius ratios where the required charge is minimized, and is significantly below the corona discharge limit of a single isolated hydrometeor. In ambient fields near 0.3Ek, where photoelectric feedback [Pasko et al., 2025, https://doi.org/10.1029/2025JD043897] can provide a sustained supply of seed electrons, this collision-mediated mechanism provides a pathway to overcome the charge-limiting constraints of isolated particles. These findings offer a consistent physical basis for the birth of lightning leaders in typical thundercloud environments.
How to cite: Jánský, J., Janalizadeh, R., and Pasko, V.: Threshold electric fields for streamer ignition from colliding charged hydrometeors in thunderstorms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22081, https://doi.org/10.5194/egusphere-egu26-22081, 2026.
From sandstorms and volcanic plumes, electrical charging of small particles is of critical importance in many geophysical settings. How do the particles in these systems become charged in the first place? In this talk, I will discuss our experimental work on the transfer of electrical charge that occurs when two solid objects are contacted and separated. We focus on oxides (e.g., SiO₂) as they are the most abundant and relevant class of materials on the earth, which presents a number of challenges. First, they are extremely hard, which means their contact areas—and hence charge exchange—are extremely small. Second, direct handling introduces spurious charge that can overwhelm the signal we wish to measure. We overcome these challenges using acoustic levitation, which enables thousands of automated, hands-free contacts and charge measurements with few-hundred-electron resolution on macroscopic samples. Our experiments reveal that oxide contact electrification is not due to any bulk material property, but instead arises from surface adsorbates—specifically adventitious hydrocarbons—acquired by objects from the air that surrounds them. These findings, now in press at Nature, are the long sought source of particulate charging in settings ranging from desert sands to volcanoes and beyond.
How to cite: Waitukaitis, S. and Grosjean, G.: Atmospheric adsorbates break symmetry in oxide electrification, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20179, https://doi.org/10.5194/egusphere-egu26-20179, 2026.
Lightning flashes are a major source of tropospheric NOx, which leads to the production of tropospheric O3 (Elshorbany et al., 2024). Tropospheric O3 is an important greenhouse gas (Skeie et al., 2020), and lightning rates are predicted to increase with global warming (e.g., Pinto & Pinto, 2020; Romps et al., 2014), creating a positive feedback loop. Laboratory-based measurements are a means to improve the parameterisation of this source to improve the accuracy of climate models.
We sampled concentrations of NO, NO2 and O3 produced following lightning generated at Cardiff University’s Lightning Laboratory, the only university-based research laboratory of its type in Europe. The laboratory generated D waveforms (peak currents ranging from 10 to 100 kA over 100 µs) and C waveforms (~250 A for 0.5 s) conforming to the EUROCAE ED-84 and its SAE equivalent standards. The D waveform represents the initial impulse and any subsequent restrikes, whereas the C represents the long-duration continuing current seen in ~10% of lightning waveforms (Pérez-Invernón et al., 2023). An array of low-cost sensors recorded gas concentrations following strikes. Despite some disruption due to the lightning Electro-Magnetic Pulse (EMP), and instances where high concentrations have saturated the sensors, initial results demonstrate the feasibility of measuring lightning NOX and O3 generation in the laboratory. This provides a foundation for future developments with a view to better quantifying the impact of lightning strikes on tropospheric chemistry and investigating how this varies with the waveform and power dissipated by the strike.
References
Elshorbany, Yasin, et al. “Tropospheric Ozone Precursors: Global and Regional Distributions, Trends, and Variability.” Atmospheric Chemistry and Physics, vol. 24, no. 21, 5 Nov. 2024, pp. 12225–12257, acp.copernicus.org/articles/24/12225/2024/?form=MG0AV3, https://doi.org/10.5194/acp-24-12225-2024.
J., Osmar Pinto, and Iara R. C. A. Pinto. “Lightning Changes in Response to Global Warming in Rio de Janeiro, Brazil.” American Journal of Climate Change, vol. 09, no. 03, 2020, pp. 266–273, https://doi.org/10.4236/ajcc.2020.93017.
Pérez-Invernón, Francisco J., et al. “Variation of Lightning-Ignited Wildfire Patterns under Climate Change.” Nature Communications, vol. 14, no. 1, 10 Feb. 2023, https://doi.org/10.1038/s41467-023-36500-5.
Romps, D. M., et al. “Projected Increase in Lightning Strikes in the United States due to Global Warming.” Science, vol. 346, no. 6211, 13 Nov. 2014, pp. 851–854, science.sciencemag.org/content/346/6211/851, https://doi.org/10.1126/science.1259100.
Skeie, Ragnhild Bieltvedt, et al. “Historical Total Ozone Radiative Forcing Derived from CMIP6 Simulations.” Npj Climate and Atmospheric Science, vol. 3, no. 1, 17 Aug. 2020, https://doi.org/10.1038/s41612-020-00131-0.
How to cite: McGurk, C., Peters, D., McCormack, E., Clark, D., Hills, M., Stone, C., and Mitchard, D.: Measuring NOx and O3 emissions from laboratory generated lightning , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20216, https://doi.org/10.5194/egusphere-egu26-20216, 2026.
A phenomenon known as a "recoil leader" has now been reliably established experimentally. Ricoil leaders manifest themselves as waves of luminosity that move toward the channel of a pre-existing bright leader [Mazur, 1989]. On the other hand, radio interferometers have detected the movement of radio emission sources within thunderclouds toward a possibly existing positive leader channel. This phenomenon is known as "needles" [Hare et al., 2019].
We propose a hypothesis that explains recoil leaders and "needles" based on the phenomena of return corona and return leaders, which were observed during experiments with long sparks (30-60 m) [Lupeiko et al., 1984; Baikov et al., 1988, Mrázek, 1996, 1998].
Qualitatively, the process can be explained as follows. As leaders propagate, a streamer corona in front of the leader tip injects charge into the volume around the leader channel (leader sheath) [Bazelyn & Raizer, 1998]. The leader channel is analogous to a high-voltage wire. As the potential on the "wire" increases, the streamer zone expands, and the charge in the sheath increases. This process continues until the electric field in the "wire" (the leader channel) is balanced by the electric field of the sheath charge. If the potential inside the leader channel drops, the sheath's electric field exceeds the channel's electric field. The electric field reverses, resulting in a return corona and/or return leaders.
This mechanism was confirmed experimentally in [Baikov et al., 1988]. The Marx generator generated a positive voltage of 3.4 MV (rise time 300 μs, pulse duration – 10 ms). The leader moved for 2.2 ms and reached a length of 45 meters. The discharge was incomplete, since the leader did not reach the grounded plane, and the leader plasma decay in the air. Despite the nearly constant voltage (after reaching 3.4 MV), each branching or rotation of the leader resulted in pulsations in the current and leader glow (the sheath exchanged charge with the leader channel). After the leader stopped, the current and glow in the gap ceased, and a dark period began, lasting at least 2 ms. The dark period ended with a series of flashes ("recoil leaders"), the glow zone of which coincided in size with the charge sheath. Each individual flash was accompanied by a current pulse of reverse polarity and a voltage surge across the Marx generator's divider capacitance. The charge neutralized in these flashes was approximately 50 μC.
Similar results at positive voltages of 3-4 MV were obtained on a Marx generator in Prague [Mrázek, 1996; 1998].
Baikov A.P. et al. (1988). Electricity, 9, 60 (in Russian)
Bazelyan, E. M., & Raizer, Y. P. (1998). Spark discharge. Boca Raton, FL: CRC Press
Hare B.M. et al. (2019). Nature, 568, 360
Lupeiko A. V. et al. (1984) Proc. of the All-Union Conf. on Gas Discharge. Tartu: TSU, 1984, v. 2. (in Russian)
Mazur V. (1989) JGR-A, 94, 3326
Mrázek J. (1996). Acta Techn. CSAV, 41, 577
Mrázek J. (1998). Acta Techn. CSAV, 43, 571
How to cite: Kostinskiy, A. and Ploc, O.: One possible mechanism for the formation of recoil leaders and "needles", EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21302, https://doi.org/10.5194/egusphere-egu26-21302, 2026.
A bolt from the blue [1,2] was observed simultaneously by ground-based video observations, space-based video with the Lightning Imager on the Meteosat Third Generation geostationary satellite (MTG-LI) [3,4], and a low-frequency lightning interferometer during field work at Sutherland, South Africa, January 28th, 2025.
The bolt from the blue was initiated by an intra-cloud discharge that connects two charged layers at the edge of a thundercloud. The stepped leader subsequently propagates horizontally away from the cloud. During the development, the lightning leader channel splits into two parts, one which propagates further away horizontally and one which returns towards the cloud but then curves down to Earth where it splits again into two separate strike points on the ground.
The ground-based video observations are paralleled by simultaneous space-based video observations with the Lightning Imager on the Meteosat Third Generation geostationary satellite (MTG-LI) with a temporal resolution of 1 ms. The illuminations of individual pixels (events) are summarised into clusters (groups) which measure the spatial extent of the bolt from the blue after correction for the parallax error using cloud top height measurements inferred from the Flexible Combined Imager (FCI) payload on MTG.
The electromagnetic emissions of the bolt from the blue are recorded with a low-frequency interferometer on the ground that consists of three radio receivers which are deployed in a triangular array, ~15 km away from the thundercloud. The radio receivers use horizontal electric field sensors (horizontal dipoles) [5] to measure the electromagnetic emissions of the bolt from the blue with 1 us resolution. These waveforms show a sequence of pulses with different shapes which indicate the occurrence of various physical processes during the development of the bolt of the blue.
The video observations from the ground and from space are compared to the recordings with the lightning interferometer and the benefits arising from these joint analyses are discussed in detail.
References:
[1] Krehbiel, P., Riousset, J., Pasko, V. et al. Upward electrical discharges from thunderstorms. Nature Geoscience 1, doi:10.1038/ngeo162, 233–237, 2008.
[2] J. Harley, L. Zimmerman, H. Edens, H. Stenbaek-Nielsen, R. Haaland, R. Sonnenfeld, and M. McHarg. High-speed spectra of a bolt from the blue lightning stepped leader. Journal of Geophysical Research, 26(3), doi:10.1029/2020JD033884, 1-10, 2021.
[3] A.M. Holzer, et al.: EUMETSAT-ESSL Application Guide on the Use of MTG LI in Severe Convective Storms Nowcasting, ESSL Report 2025-01, https://www.essl.org/cms/essl-testbed, 2025.
[4] M. Füllekrug, E. Williams, C. Price, S. Goodman, R. Holzworth, S.-E. Enno, and B. Viticchie, Novel lightning flash densities from space [in “State of the Climate in 2024”, Bulletin of the American Meteorological Society, 106 (8), doi:10.1175/2025BAMSStateoftheClimate.1, S85–S86, 2025.
[5] M. Füllekrug, M. Kosch, G. Dingley, X. Bai, and L. Macotela. Six-component electromagnetic wave measurements of sprite-associated lightning. ESS Open Archive, doi:10.22541/essoar.176296584.41929367/v1, 2025.
Acknowledgments:
The authors wish to thank Sven-Erik Enno from EUMETSAT for assistance with the MTG-LI data retrieval. The MTG-LI data used for this study were kindly provided by EUMETSAT from https://user.eumetsat.int/resources/user-guides/mtg-data-access-guide
How to cite: Fullekrug, M. and Kosch, M.: Bolt from the blue caught on video, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21746, https://doi.org/10.5194/egusphere-egu26-21746, 2026.
Lightning continues to challenge high-voltage transmission reliability, accounting for approximately 40-60% of recorded line trips. However, the lightning nowcasting and short-term warning products currently used in power grid operations often provide insufficient lead time for actionable transmission-line protection and dispatch.
Here we integrate a 10-year utility dataset of lightning-induced 500 kV transmission line trips in North China with cloud-to-ground (CG) lightning observations and ERA5 reanalysis to quantify the 12 h pre-event evolution of the atmospheric environment. We define three 12-h pre-event samples using different reference points: (i) Line trips (LT) cases centred on the trip location; (ii) Thunderstorms without line trips (WLT) cases centred on the tower closest to where a thunderstorm intersects the line corridor; and (iii) Non-thunderstorm (NT) controls centred on the same tripping location, sampled at the same local time within ±7 days of each LT event under lightning-free conditions in the preceding 12 h.
Compared with NT controls, both LT and WLT events occur in a more convectively favourable environment, with higher total column water vapour (TCWV), convective available potential energy (CAPE), and lower lifting condensation level (LCL). They also show stronger lifting—more negative 700 and 850 hPa vertical velocity and enhanced low-level convergence. Within thunderstorms, however, LT events tend to occur in an instability-dominated regime, with higher CAPE and steeper 700-500 hPa temperature lapse rates than WLT events. By contrast, WLT events are more “water-loaded,” showing higher TCWV and stronger integrated water vapour transport (IVT), together with stronger lifting—yet weaker CAPE and lapse rates.
These results suggest that instability-focused precursors can help discriminate tripping risk and motivate environment-based indicators to extend operational lead time for transmission line lightning protection.
How to cite: Li, M., Wang, J., Fan, Y., Huang, Y., Li, Q., and Li, Y.: Thermal Instability as a Critical Precursor to Transmission Line Lightning Trips: A 12-Hour Pre-Event Analysis in North China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15307, https://doi.org/10.5194/egusphere-egu26-15307, 2026.
We present observations of small-scale discharges, or sparks, within thunderstorms before the initiation of a lightning leader. Using LOFAR A-TRID, which provides exceptional precision and accuracy through near-field beamforming with hundreds of antennas [1], we detected multiple spark-like discharges with varying characteristics. Some show a collective propagation direction, with some speeds as low as 1 x 106 m/s (similar to ultra-slow propagation), and some as fast as 1 x 107 m/s [2, 3]. As these sparks occur in a kilometer sized region adjacent to the initiation region, they could be used to map the extent of high-field regions within thunderstorms. These results suggest that failed initiation events may be infrequent and difficult to detect as they occur in sparse clusters on short spatiotemporal scales. This work will provide an overview of the physical properties of the spark discharges and implications for lightning initiation.
1: Olaf Scholten, Steven A. Cummer, Joseph R Dwyer, et al. A Comprehensive analysis of High Resolution VHF Observations with LOFAR of the Positive Initiating Event for Several Lightning Flashes. ESS Open Archive . December 12, 2025.
2: Sterpka, C., Dwyer, J., Liu, N., Demers, N., Hare, B. M., Scholten, O., & ter Veen, S. (2022). Ultra-slow discharges that precede lightning initiation. Geophysical Research Letters, 49, e2022GL101597. https://doi.org/10.1029/2022GL101597
3: terpka, C., Dwyer, J., Liu, N., Hare, B. M., Scholten, O., Buitink, S., et al. (2021). The spontaneous nature of lightning initiation revealed. Geophysical Research Letters, 48, e2021GL095511. https://doi.org/10.1029/2021GL095511
How to cite: Sterpka, C., Hare, B., Scholten, O., Turekova, P., Lourens, M., Wu, B., Dwyer, J., Liu, N., and Cummer, S.: Small-Scale Discharges in the Thunderstorm Prior to Lightning Initiation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13571, https://doi.org/10.5194/egusphere-egu26-13571, 2026.
Separation of charge via noninductive ice-ice collisions in clouds is widely accepted as the primary mechanism behind cloud electrification. However, not all clouds end up with the same charge distributions, as observed in various field campaigns and laboratory experiments over the last several decades. The distribution of charge in a given thunderstorm controls the polarity, frequency, and other characteristics of lightning produced by that storm, but charge distribution is very difficult to measure directly, especially at statistically significant scales. Of particular interest to the lightning community is the relationship between thunderstorm environments and lightning characteristics, where the charge distribution of storms bridges the gap between the two. This study will use intracloud (IC) lightning data from the Earth Networks Total Lightning Network (ENTLN) to investigate the statistical relationships between the proportion of negative IC flash frequency to environmental parameters such as charge reversal temperature altitudes, cloud base height, cloud depth, and warm vs cold cloud depth fraction derived from global reanalysis data for multiple regions around the world
How to cite: DiGangi, E., Ringhausen, J., Lapierre, J., and Zhu, Y.: Statistical Relationships between Negative Intracloud Flash Fraction and Environmental Parameters Controlling Cloud Electrification, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22197, https://doi.org/10.5194/egusphere-egu26-22197, 2026.
In recent years, it has been pointed out that there has been an increase in the number of localised heavy rain and hailstorms in urban areas, which are thought to be caused by climate change and extreme weather. It is said to be difficult to distinguish whether a thundercloud (cell) that causes localised hailstorms or heavy rain is a cell that will produce hailstorms or heavy rain, based on observations of the reflection intensity of the weather radar alone. In this study, we consider extreme weather events that cause hailstorms and heavy rain from the perspective of lightning discharges, distinguishing between cells that lead to hailstorms and cells that do not lead to hailstorms but only to heavy rain. We compared two cells in the same meteorological field in three cases that occurred in the Tokyo metropolitan area. We compared the cells that led to hailstorms with the control cells that only led to heavy rain. As a result, we found the following common characteristics.
1) The number of ±CG strokes in cells with heavy rain but no hail is larger than in cells with hail.
2) The volume of ice calculated from polarimetric radar in cells with hail is larger than in cells with heavy rain but no hail.
As a result, the possibility of discriminating between cells with and without hail has increased. This study is a re-evaluation of the results obtained by Fujiwara et al, (J. Atmos. Electriciy, 2021; 2023).
How to cite: Kamogawa, M., Fujiwara, H., and Suzuki, T.: Characteristics of atmospheric electricity of thunderclouds accompanied by severe hailfall, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16186, https://doi.org/10.5194/egusphere-egu26-16186, 2026.
This study utilizes the Earth Networks Total Lightning Network (ENTLN) combined with the Geostationary Lightning Mapper (GLM) to investigate lightning activity in hurricanes relative to hurricane structure and evolution for 5 years of hurricane seasons. This combination enables a more complete estimate of lightning activity than one detection method can provide alone, including the derivation of the cloud flash fraction (CFF) for each hurricane. Additionally, lightning characteristics for each individual hurricane as well as average trends and correlations to hurricane wind speed and brightness temperatures are explored. Overall, this research has the potential to provide further insight into tropical cyclone intensification and weakening.
How to cite: Ringhausen, J., Haliczer, D., Lapierre, J., DiGangi, E., and Zhu, Y.: Relationship Between Lightning Characteristics and Hurricane Intensity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22200, https://doi.org/10.5194/egusphere-egu26-22200, 2026.
Lightning plays a critical role in the Earth system by shaping biogeochemical cycles, while also posing significant natural hazards and serving as a key geophysical indicator for storm monitoring and wildfire early warning. However, existing publicly available global lightning datasets are often limited in either spatial or temporal resolution and do not distinguish between intra-cloud (IC) and cloud-to-ground (CG) lightning, restricting their applicability for many scientific studies. Here, we present a newly developed global gridded lightning dataset, the Flash Location Aggregation from Strokes into a High-resolution Multi-scale Analysis Product (FLASHMAP). FLASHMAP is derived from lightning observations provided by Vaisala’s Global Lightning Detection Network (GLD360) and currently covers the period from 2019 to 2024. A gridding framework is applied to convert point-based lightning stroke detections into multi-scale products at 0.1° hourly, 0.25° daily, and 0.5° monthly resolutions. FLASHMAP provides comprehensive lightning characteristics, including counts of IC and CG strokes and flashes, stroke location uncertainty and peak current, and flash multiplicity. FLASHMAP can report more total lightning strokes than existing global lightning products in most of the land regions. Comparisons with regional lightning detection networks in Alaska (USA), Spain, and New South Wales and the Australian Capital Territory (Australia) indicate that FLASHMAP reports comparable CG stroke counts while detecting fewer IC strokes. FLASHMAP is expected to advance interdisciplinary research on global and regional lightning climatology, lightning-ignited wildfires, thunderstorm identification, and ecosystem impacts.
How to cite: Qu, Y., Brambleby, E., Janssen, T., Moris, J., Hunt, H., Joshi, M., Mataveli, G., Pérez-Invernón, F., Said, R., Yebra, M., Zhao, L., Jones, M., and Veraverbeke, S.: FLASHMAP: A new global gridded lightning dataset with high spatial and temporal resolution, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5328, https://doi.org/10.5194/egusphere-egu26-5328, 2026.
We introduce the Lightning Differential Space (LDS) framework for multiscale, data-driven characterization of cloud-to-ground (CG) lightning, in which consecutive stroke intervals are mapped into a two-dimensional space spanned by their spatial and temporal derivatives. Using Earth Networks Total Lightning Network (ENTLN) observations, we analyze CG strokes during peak lightning seasons (2020–2021) across three climatically distinct regions: the Amazon (tropics), the Eastern Mediterranean Sea (subtropics), and the northern U.S. Great Plains (mid-latitudes).
The LDS topography reveals a robust and regionally consistent “allowed” and “forbidden” zones, with dominant clusters separating intra-flash successive strokes from inter-flash intervals at thundercloud and cloud-system scales. While the overall structure is stable across regions, systematic shifts in cluster location and separability reflect contrasting convective environments, including differences in characteristic inter-event times and system-scale distances.
We further introduce a Current Ratio LDS, which projects the ratio of absolute peak currents between successive strokes onto the same stroke interval coordinates. This diagnostic acts as a statistical partitioning tool that sharply distinguishes intervals likely to contain flash-initiating strokes (where the succeeding stroke tends to be stronger) from intervals dominated by subsequent strokes within multi-stroke flashes. Across all regions, a distinct short time interval feature (< ~0.02 s) spans distances from sub-kilometer to hundreds of kilometers, suggesting rare near-simultaneous remote CG events and motivating renewed investigation of long-range thunderstorm coupling (teleconnection).
Overall, the LDS framework (combining number distribution and current ratio information) provides a scalable pathway for extracting coherent multiscale lightning behavior from large network datasets, with direct relevance for evaluating model representations of stroke and flash processes and for developing diagnostics supporting probabilistic monitoring and nowcasting.
How to cite: Altaratz, O., Ben Ami, Y., Yair, Y., and Koren, I.: Diagnosing stroke, flash, and storm scale lightning variability using Lightning Differential Space, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9083, https://doi.org/10.5194/egusphere-egu26-9083, 2026.
Lightning is an important disturbance process in forest ecosystems, affecting trees both directly—when a strike kills a tree—and indirectly by igniting wildfires. While lightning–fire interactions are widely studied, direct lightning-induced tree mortality is not represented in global Earth System Models, limiting our ability to assess the full impact of lightning on forests under a changing climate.
To address this gap, we implement lightning-induced tree mortality in the dynamic global vegetation model LPJ-GUESS, using field-derived relationships from a Panamanian forest where lightning mortality has been systematically quantified. The model successfully reproduces observed lightning-induced tree mortality at several sites but simulates lower mortality than estimated at other locations. Running the model globally, we quantify the number of trees and associated biomass directly lost to lightning and compare these losses to biomass losses from lightning-ignited wildfires, highlighting key uncertainties in both pathways.
To place these present-day impacts in a future context, we synthesize existing lightning parameterizations used in global chemistry-climate models and assess their skill and projected changes in lightning activity. Applying projections from several well-performing parameterizations, we explore how future changes in lightning may alter both direct and indirect lightning-induced tree mortality. Together, our results demonstrate that lightning is a multifaceted and potentially growing driver of forest change, and that accurately representing lightning mortality is essential for robust projections of future forest dynamics.
How to cite: Krause, A., Gregor, K., Meyer, B., and Rammig, A.: Lightning impacts on forests: direct and indirect (wildfire) tree mortality under present and future lightning activity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11696, https://doi.org/10.5194/egusphere-egu26-11696, 2026.
It has been known for many decades that nitrogen oxide compounds (NOx) are formed by lightning flashes due to the high temperatures in the lightning channel, which allows the otherwise tightly bounded N2 and O2 to react with each other. Lightning NOx is then oxidized in cloud and rain drops to form nitric acid and deposited at the surface as nitrate (NO-3) in precipitation. This nitrate is a form of fixed nitrogen that can be taken up by ecosystems, especially where biological N fixation is limited.
Since 2011, researchers have repeatedly observed the so-called Great Atlantic Sargassum Belt, a gigantic carpet of seaweed that drifts from the equator towards the Caribbean when easterly winds prevail. Until now, the sources of nutrients fueling their rapid growth are unclear. It was hypothesized that nutrient runoff from overfertilization and rainforest deforestation might be responsible or upwelling of phosphorus-rich deep waters. However, these processes cannot completely explain the increase in Sargassum biomass observed during the past years. Nitrogen is a key element governing the dynamics and function of many ecosystems as many of them are limited in biologically available nitrogen supply. The lack of N is an important inhibitor on primary production in the tropics. Owing to this limitation, an increase in available N from lightning could increase the primary production and biomass accumulation.
Our analysis of the spatial distribution of lightning and Sargassum blooms over the tropical Atlantic show remarkable agreement during specific months of the year, as well as the annual cycle of the blooms that peak in the northern hemisphere summer. While global lightning activity is expected to increase with rising global temperature, it is not clear that there has been a significant increase in lightning over the Atlantic in recent decades. Nevertheless, lightning has not yet been considered as a possible source of nitrogen impacting the Sargassum blooms.
How to cite: Price, C., Shay, A., and Golberg, A.: Is Lightning a driver of the Sargassum blooms in the Atlantic?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22205, https://doi.org/10.5194/egusphere-egu26-22205, 2026.
Although strong electric fields have been observed in lightning clouds, these fields are well below the limit to spontaneously initiate a spark that could be the beginning of a lightning flash. Understanding the lightning initiation process is thus one of (if not The) main topics in lightning research.
In this work we present very high frequency (VHF) radio observations using the LOFAR radio telescope [1]. Because of the high resolution and high sensitivity of LOFAR we could observe the faint initiating event for multiple lightning flashes. The new imaging procedure (called ATRI-D) was shown to be able to distinguish different emission sites of VHF pulses on an airplane flying at an altitude of 8 km [2].
The propagating tip of this apparent initiating event carries positive charge, as is generally expected. Our observations show that the propagation speeds of this positive initiating event (PIE) are very similar at about 5 x 10^6 m/s. Very surprisingly, both the e-folding rates in VHF-intensity and peak intensities differ significantly for the investigated flashes and show no correlation with altitude. Additionally, these structures are extremely narrow, with diameters under 0.8 meters, and maintain this confinement over propagation distances exceeding 100 meters. Even more surprising is that subsequent dart leaders do not follow the path of the PIE, implying that the PIE has not formed a well-conducting structure and does not transform into a positive leader.
Lightning initiation is shown to be a very subtle process, in spite of the vigor of a lightning flash, and the high resolution and sensitivity of LOFAR shows, for multiple lightning flashes, that the initiating event is a very weakly radiating, positively charged propagating structure.
1) Olaf Scholten, Steven A. Cummer, Joseph R Dwyer, et al.; A Comprehensive analysis of High Resolution VHF Observations with LOFAR of the Positive Initiating Event for Several Lightning Flashes. ESS Open Archive . December 12, 2025. https://doi.org/10.22541/essoar.176556304.42772793/v1
2) O. Scholten, M. Lourens, et al. (2025) ; Measuring location and properties of very high frequency sources emitted from an aircraft flying through high clouds. Nature Communications, 16 (1), 10572. https://doi.org/10.1038/s41467-025-65667-2
How to cite: Scholten, O., Cummer, S., Dwyer, J., Hare, B., Liu, N., Lourens, M., Nelles, A., Sterpka, C., Turekova, P., and Wu, B.: A Comprehensive analysis of lightning Initiation with LOFAR, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6448, https://doi.org/10.5194/egusphere-egu26-6448, 2026.
The polarization of VHF radio emissions from lightning offers valuable insight into the complex physics of lightning propagation by revealing the orientation of streamer-driven VHF radiation. Measuring and interpreting this polarization, however, remains challenging. In this work, we use the LOFAR radio telescope in combination with the latest near-field beamforming technique (A-TRID) that coherently combines antenna voltages while incorporating the full antenna response. This approach enables three-dimensional reconstruction of both the location and polarization of VHF lightning sources. In this presentation, we assess the accuracy of these results by means of a Monte Carlo error analysis. We simulate antenna voltage signals produced by a point-like dipole and an extended source, a cluster of indentical dipole emitters. Subsequently, we reconstruct them using the imaging algorithm. By comparing the reconstructed source parameters with the known inputs, we obtain an estimate of the location and polarization uncertainties. For point sources, we observe a sub-meter reconstruction accuracy in three-dimensional location; and an average one-degree reconstruction accuracy in three-dimensional polarization. These values vary with the source location and with the angle between the polarization vector and the radial vector. For extended sources, we see the reconstructed location (the source size) is smaller than the input; by up to a factor of two. The polarization reconstruction accuracy is different along the two axes; a sub-degree reconstruction accuracy along the azimuthal direction and an average 7.5-degree reconstruction accuracy along the zenithal direction. This report offers a comprehensive evaluation of the results, alongside a breakdown of our technical approach and algorithmic framework.
How to cite: Turekova, P., Hare, B., Scholten, O., Lourens, M., Sterpka, C., Cummer, S., Dwyer, J., and Liu, N.: How Accurately Does LOFAR Reconstruct Lightning? Point and Extended Source Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9545, https://doi.org/10.5194/egusphere-egu26-9545, 2026.
In this work, we use lightning observations obtained by the LOFAR radio telescope to investigate the propagation dynamics of High Altitude Negative Leaders (HANLs), which have altitudes above 7 km. Operating in the very high frequency (VHF) range, LOFAR can probe lightning processes
occurring deep within the cloud at high altitudes with sub-meter precision and 100 ns integration times [2].
HANLs exhibit step lengths exceeding 100 m, an order of magnitude larger than those of negative leaders observed at lower altitudes [1]. The plasma processes underlying these HANL steps remain unknown, and it is unclear whether HANLs propagate through the same mechanism as lower altitude negative leaders. To study these structures with enhanced precision and sensitivity, we apply ATRI-D, a near-field interferometric beamforming algorithm, to LOFAR data.
Our observations reveal that the dynamics of HANL steps is increasingly complex at smaller scales. At large scales (kilometers and tens of milliseconds), HANL propagation appears as a sequence of discrete corona flashes. In contrast, on smaller scales (tens of meters and milliseconds), these “corona flashes” resolve into several branched networks of filaments that initiate at different times and locations. In addition, we find that each branched network begins with an intense VHF pulse occurring within 10 m of a previously formed filament. We will discuss some of the potential physics implications of these results.
[1] O. Scholten et al.; Distinguishing features of high altitude negative leaders as observed with LOFAR. Atmospheric Research, 260:105688, October 2021. ISSN 0169-8095. doi: 10.1016/j.atmosres.2021.105688.
[2] O. Scholten, M. Lourens et al.; Measuring location and properties of very high frequency sources emitted from an aircraft flying through high clouds. Nature Communications, 16(1), November 2025. ISSN 2041-1723. doi: 10.1038/s41467-025-65667-2.
How to cite: Lourens, M., Hare, B., Scholten, O., Sterpka, C., Turekova, P., Wu, B., Cummer, S., Dwyer, J., and Liu, N.: Fine-Scale Structure of High-Altitude Negative Leader Steps, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11132, https://doi.org/10.5194/egusphere-egu26-11132, 2026.
Extending on the complete radiation patterns of the bremsstrahlung process involving bremsstrahlung asymmetry and Doppler shift. The mathematical model is simplified, preserving the forward-backward peaking radiation properties and involved asymmetries to help model the tendency of rotation in the wavefront of the emitted wave. Results show that the curl of the gradient of the radiation intensity is non-zero, and the wavefront of the bremsstrahlung radiation follows a tapered spiral wavefront in 2D and a tapered helical wavefront in 3D. The radius of the backward rotational wavefront was found to decrease as the wave propagates. Spiral geometry has different magnitudes of radius as the wavefront rotates as a result of the involved bremsstrahlung and Doppler asymmetries. This is further supported diagrammatically by applying Huygen's principle on a relativistic radiation pattern. Outcomes describe why the lightning discharges display a partial temporal and spatial coherence, hence why lightning sferics are not known to produce structured wavefronts. Bremsstrahlung emissions start with a backward rotating and irregularly shrinking radius wavefront. Therefore, spatial coherency degrades as their tapered helical structure breaks down due to the irregular shrinkage of radius, leaving the bremsstrahlung radiation with partial temporal coherency. Rotation always starts from the shorter, bremsstrahlung symmetric lobe.
Momentum transfer from particle to rotating wavefront photon, quantized via conservation of momentum, pf - pi = - ΔPfield , and ΔPfield = (n' - n) ℏ k = Δn ℏ k, hence pf = pi - Δn ℏ k where pi, and pf are initial and final particle momentum. Hence, the relationship between bremsstrahlung asymmetry, R, as a function of the whole-number multiple of the quantum of action "n", R(n), is found. A whole multiple of the quantum of action "n" is tuned, until the correct scale of the graph, for the bremsstrahlung asymmetry quantity, R, matches the classical prediction describing the asymmetry in radiation lobes due to the particle's curved trajectory. This allowed predicting the whole number multiple of the quantum of action "n", which is n ≅ 6.3 × 1010, following the Bohr correspondence principle. Since tuning is performed with the parameter whole multiple of the quantum of action "n", which only comes with the photon orbital angular momentum, this gives the traits of a rotating wavefront.
Position vector, r, is a function of bremsstrahlung asymmetry, R, which does not include the Doppler shift in its formulation. The results demonstrate the discovery of the Doppler asymmetry within the equation that relates the bremsstrahlung asymmetry, R, to the multiples of the quantum of action, n. This indicates that the two asymmetries are related to each other, which is explained using the idea that once there is an asymmetry about one axis of symmetry of an object, automatically, there are asymmetries about the other remaining axes of symmetry of the same object. Unless the center of what is causing asymmetry does not lie exactly on the symmetry axes (Otherwise, everything would be symmetric again), which is not the case with Bremsstrahlung radiation patterns.
How to cite: Yucemoz, M.: How and Why Do Lightning Sferics have Unstructured Wavefronts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-38, https://doi.org/10.5194/egusphere-egu26-38, 2026.
Mini-EUSO is a space-based ultraviolet telescope operating aboard the International Space Station since 2019 as part of the JEM-EUSO Programme. The instrument monitors the Earth’s night-time atmosphere in the 290–430 nm wavelength range with a temporal resolution of 2.5 μs and a ground spatial resolution of approximately 5–6 km. In addition to its high time resolution, Mini-EUSO combines imaging capabilities with high sensitivity, enabled by a 25 cm diameter optical system, allowing the detection of fast and faint UV emissions associated with atmospheric electrical activity.
In this contribution, we present the analysis of a population of fast, short-duration UV transients, referred to as Short Light Transients (SLTs), with typical timescales between 100 μs and 200 μs detected by Mini-EUSO. These events are stationary within the spatial resolution of the detector and are frequently followed, at the same geographical location, by additional atmospheric emissions occurring within 1–200 ms. The observed temporal correlations and spatial localization suggest a connection with rapid atmospheric electrical processes, potentially related to lightning activity or to early-stage or precursor phenomena associated with transient luminous events.
The combination of microsecond-scale temporal resolution, imaging capability, and high optical sensitivity makes Mini-EUSO particularly well suited for the investigation of fast, localized UV emissions that are challenging to observe with conventional lightning and atmospheric monitoring instruments.
In addition to the SLTs discussed here, Mini-EUSO has recorded a wide range of lightning-related and transient luminous phenomena, highlighting the potential of space-based UV observations for the study of fast electrical processes in the atmosphere.
How to cite: Battisti, M.: Short Light Transients and millisecond-scale follow-up emissions observed by Mini-EUSO, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19685, https://doi.org/10.5194/egusphere-egu26-19685, 2026.
After more than three decades of research on transient luminous events (TLEs), typical electrical and dynamical properties of the thunderstorms responsible for their production are still not completely understood. The reliability of prediction when and where TLEs occur is very limited, as numerous case studies focus only on individual TLE-producing storms.
To contribute to these efforts, we analyze 34 TLE-producing storms observed between 2018 and 2020 in Central Europe, each generating at least ten TLEs, specifically sprites and halos. Using products from the Nowcasting and Very Short Range Forecasting Satellite Application Facility (NWC SAF), we follow the full life cycle of each storm, from initiation to dissipation, defining storm boundaries by the presence of very high opaque clouds. Lightning activity and its temporal evolution are derived from LINET lightning detections within the identified storm boundaries. Cloud-top temperature and cloud-top height products are used to relate TLE occurrences to the convective structure of the storm. Statistical distributions of these parameters are compiled at TLE locations.
We show that TLEs statistically appear after the peak of cloud-to-ground lightning activity and at preferred locations relative to storm evolution. Rather than being distributed uniformly over the storm, TLEs are spatially confined to relatively small regions, forming clusters with typical horizontal dimensions of approximately 0.5° × 0.5° in geographic lat–lon coordinates. These regions exhibit persistence in time, as repeated TLE occurrences are frequently observed within the same localized areas of the storm, separated by up to several tens of minutes. Such preferred regions are most commonly located near the convective core, within the stratiform region, and above areas of former convective activity. Additionally, we classify the analyzed storms by area and morphological characteristics, providing insight into the storm structures most favorable for TLE production.
How to cite: Barotová, K., Kolmašová, I., Pišoft, P., and Popek, M.: Meteorological and Lightning Characteristics of Thunderstorms Producing Transient Luminous Events, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6296, https://doi.org/10.5194/egusphere-egu26-6296, 2026.
Previous studies have demonstrated that electrodynamic effects can sometimes be important in simulations of elves, sprite halos, and sprite initiation. To examine the extent to which such effects contribute to the evolution of regions of possible sprite inception, we extend our fully three-dimensional quasi-electrostatic (QES) model of the electric field above thunderstorms to include dynamic effects. The original QES model employed the method of images for every charge in the domain at every time step, eliminating the need for spatial finite differencing of the electric potential or electric field and yielding a numerically stable and accurate solution of the QES equations (see, e.g., Haspel and Yair, 2025; doi:10.1016/j.asr.2025.01.013). In the present implementation, we add the electric induction (“velocity”) term to the Coulomb term in the expression for the electric field produced by each charge in the domain. In addition, we replace instantaneous time with retarded time, such that the model is also fully causal; a change in charge density at point A does not manifest in a change in the electric field at point B until that “signal” has time to propagate from A to B. The resulting Coulomb and induction contributions are structurally equivalent to the corresponding terms in Jefimenko’s formulation. This approach lies between traditional QES models and full-wave electromagnetic models and may be described as quasi-electrodynamic rather than quasi-electrostatic. It allows induction and causality effects to be included throughout the entire domain without spatial finite differencing and without an explicit representation of the lightning channel as used in transmission-line or EMP models. We find that the inclusion of causality delays the formation of regions of possible sprite inception and, together with the induction term, produces regions that persist longer than in traditional QES simulations with otherwise identical simulation parameters. Initial results from this extended model will be presented and discussed.
How to cite: Haspel, C.: A quasi-electrodynamic model for examining the effects of induction and causality in simulating regions of possible sprite inception in the mesosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14177, https://doi.org/10.5194/egusphere-egu26-14177, 2026.
The Pierre Auger Observatory has detected downward terrestrial gamma-ray flashes (TGFs) with its water-Cherenkov detectors. Understanding this high-energy radiation occurring during thunderstorms requires combining such measurements with observations of lightning processes in their earliest stages. To meet this challenge, the Broadband Observatory of Lightning and TGFs (BOLT) is currently under construction to image lightning propagation in three dimensions with high time resolution using radio interferometry, extending the unique multi-detector capabilities of the Pierre Auger Observatory.
BOLT is based on eleven modified Auger Engineering Radio Array (AERA) stations operating in the 30–80 MHz bandwidth and deployed at strategic locations within the Auger array. While the AERA stations by themselves already provide the necessary spatial and timing resolution, a key modification for BOLT is the implementation of a long buffer readout. This capability enables the reconstruction of lightning development and the correlation of radio emissions with TGF-related signals observed by the Observatory’s water-Cherenkov detectors.
This contribution presents recent hardware developments, including the long buffer readout, progress toward selective triggering and precision timing, and first field data analyzed using insights from previous AERA measurements, illustrating the growing capability of BOLT for combined lightning and TGF studies. Together with the existing detector systems of the Pierre Auger Observatory, BOLT establishes a powerful experimental framework for advancing our understanding of lightning physics and associated high-energy atmospheric phenomena.
How to cite: Weitz, M. J. and the Pierre Auger Collaboration: BOLT: Imaging Lightning and Terrestrial Gamma-ray Flashes at the Pierre Auger Observatory, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10336, https://doi.org/10.5194/egusphere-egu26-10336, 2026.
Mini-EUSO (Multiwavelength Imaging New Instrument for the Extreme Universe Space Observatory) is a compact ultraviolet telescope operating aboard the International Space Station since 2019, observing the Earth’s atmosphere in the 290-430 nm band from nadir. It is a part of the JEM-EUSO programme, aimed at developing technologies for the observation of ultra-high-energy cosmic rays (UHECRs) from space. The instrument comprises two 25 cm Fresnel lenses and a focal surface of 36 multi-anode photomultiplier tubes (2304 pixels), providing a 44° field of view and a time resolution of 2.5 μs. With an angular pixel size of ∼0.86°, Mini-EUSO has a spatial resolution of ∼6 km at ground level and ∼5 km at ionospheric altitudes, allowing for detailed imaging of fast transient luminous events.
Since the beginning of operations, Mini-EUSO has recorded approximately 50 ELVES. A large fraction of the observed events exhibit complex morphologies, most notably multi-ring structures. Understanding the diversity of ELVES morphologies requires quantitative measurements of their dynamics (ring radius and expansion speed), energetics, and internal ring morphology.
We present results from a dedicated analysis pipeline that reconstructs the spatio-temporal development of ELVES UV emission at microsecond time scales. Mini-EUSO’s fast imaging allows us to measure ring properties such as thickness and brightness variations along the ring, and to follow how these features evolve in time. These measurements help constrain ELVES production mechanisms and the relative role of different EMP propagation paths. In several cases, the reconstructed timing and ring morphology are compatible with, and suggest, a “ground reflection” contribution, where additional ELVES rings may be associated with an EMP component reflected from the Earth’s surface. These observations highlight the capability of compact space-based UV instruments to advance ELVES physics and to probe EMP-ionosphere coupling with unprecedented detail.
How to cite: Plebaniak, Z.: Probing lightning-ionosphere coupling with Mini-EUSO: timing and morphology of multi-ring ELVES, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20296, https://doi.org/10.5194/egusphere-egu26-20296, 2026.
Thunderclouds are the largest natural gamma-ray laboratories on Earth, producing a large variety of gamma-ray phenomena of different shape, duration, and intensity. In our previous parametric study of a 0.5D fluid model of relativistic runaway electrons (RRE) in a thundercloud high-field region [1] – based on relativistic feedback discharge (RFD) theory [2] – we systematically reproduced the entire zoo of thundercloud gamma-ray signals, including the flickering gamma-ray flashes (FGFs) as detected by ALOFT [3], indicating that RFD may potentially play a significant role in these phenomena.
Here we present a new relativistic fluid model based on the same principles but expanded to include the non-uniformity along the vertical axis, allowing us to explore the effects of more realistic space charge distributions as well as simulating and comparing hard radiation signals from high-field regions with both negative and positive polarities. In addition to solving continuity equations for RRE and ions (as the 0.5D model did), this model also includes equations for positrons as well as upward- and downward-propagating photons, making it possible to estimate the flux of positrons compared to electrons as well as mimicking gamma-ray light-curves directly from the simulated photon density. While the 0.5D model provides excellent qualitative results regarding hard-radiation produced with (or without) the help of RFD, we expect this new model to give better quantitative results, for instance a better idea regarding the minimum charge layer separation distance needed to reproduce ALOFT’s FGFs. With this model, we should also be capable of forward-modelling radio and optical signals, which will make it easier to distinguish (multi-pulse) terrestrial gamma-ray flashes (TGFs) from FGFs. That could ultimately also give us a better insight into whether TGFs could be produced solely by RFD.
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[1] Ø. H. Færder, N. Lehtinen, D. Sarria, M. Marisaldi, N. Østgaard, I. Bjørge-Engeland, and A. Mezentsev. Numerical parameter-space studies of various types of thundercloud gamma-ray emissions. ESS Open Archive eprints, 776:essoar.175578737, Aug. 2025. doi:10.22541/essoar.175578737.77602064/v2.
[2] Dwyer, J. R., “Relativistic breakdown in planetary atmospheres,” Physics of Plasmas, vol. 14, no. 4, p. 042901 (2007).
[3] 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).
How to cite: Færder, Ø. H., Lehtinen, N., Sarria, D., Marisaldi, M., and Østgaard, N.: A relativistic fluid model for reproducing thundercloud hard radiation including ALOFT’s flickering gamma-ray flashes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9916, https://doi.org/10.5194/egusphere-egu26-9916, 2026.
Predicted by Wilson in the 1920s, thunderstorms act as natural particle accelerators. Charged particles, mainly electrons, can be energized by the strong electric fields inside thunderclouds, becoming runaway electrons that reach relativistic energies. During this acceleration, these relativistic electrons produce secondary electrons through atmospheric ionization, leading to a Relativistic Runaway Electron Avalanche (RREA) while emitting X-rays through bremsstrahlung. This mechanism underlies the high-energy atmospheric phenomena generated by thunderstorms, such as terrestrial gamma-ray flashes (TGFs), flickering gamma-ray flashes (FGFs), and gamma-ray glows (GRGs).
GRGs are long-lasting X-ray emissions produced by sustained RREAs, typically lasting from seconds to tens of minutes. They are usually observed close to their sources either by aircraft, high-altitude sites located on mountain, or from the western coast of Japan where thunderclouds frequently develop near sea level.
Since 2023, we are conducting a ground-based observational campaign by equipping several strategic sites to detect these high-energy events and study their occurrence and characteristics. Three sites were instrumented with scintillators: Chofu (Tokyo, Japan), Pic du Midi de Bigorre (French Pyrenees), and Normandy (France).
In this presentation, we introduce a new statistical method designed to detect GRGs and potentially TGFs and FGFs. The method combines Gaussian filtering, continuous wavelet transforms, and Bayesian inference. It enabled the detection of more than ten GRGs at Pic du Midi between April and November 2025, as well as two GRGs at sea level in Chofu and Normandy demonstrating the method’s efficiency and showing that GRGs are common and associated with all thunderstorms.
How to cite: Hazem, Y., Celestin, S., Trompier, F., Hobara, Y., and Defer, E.: Gamma-Ray Glows: A Common Signature of Thunderstorms ?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7355, https://doi.org/10.5194/egusphere-egu26-7355, 2026.
Detection of lightning discharges on Jupiter and the estimation of their energy have been the subject of numerous studies using data from variety of spacecraft and probe instruments, operating mostly in the optical range. Individual datasets, however, report markedly different numbers of detected events and characteristic energies, largely due to differences in sensitivity, accumulation time and spatial coverage of individual instruments.
To provide a more unified view of optical lightning observations made by Voyager 1&2, Galileo, Cassini, New Horizons and Juno SRU, we use lightning density evaluated on the visible surface as a common metric. By dividing the energy range into logarithmically spaced bins, we compute the lightning density within each interval. This approach enables a direct comparison between instruments with different sensitivities and reveals a consistent log-normal distribution of lightning energies across multiple datasets.
Detections of lightning-generated whistlers on Jupiter by the Juno mission are substantially more prevalent than all previous optical detections. Unlike optical observations, the sensitivity of radio measurements is not constant. It varies by several orders of magnitude depending on the spacecraft’s position and local plasma conditions, complicating detection statistics.
We introduce also a method to estimate the minimum detectable whistler energy in individual Juno Waves LFR-Lo snapshots. The method is based on modeling the background incoherent noise, including both instrumental and natural contributions. Artificial whistler waveforms with known properties are injected into the modeled noise to test detectability and to evaluate the performance of the Poynting vector measurement.
By this approach, we are able to compare lightning density as a function of energy for both optical and radio wavelengths.
How to cite: Rosicka, K., Santolík, O., Kolmašová, I., and Imai, M.: Surface density of lightning discharges on Jupiter as a function of their energy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5138, https://doi.org/10.5194/egusphere-egu26-5138, 2026.
The JUpiter ICy moons Explorer (JUICE) is an ESA-led mission that will investigate Jupiter’s atmosphere and the potential habitability of the Galilean satellites in 2031-2035 (Grasset et al., 2013). One of the goals of the investigation of Jupiter’s atmosphere is to determine the spatial distribution, frequency and intensity of lightning, providing a global picture of convective phenomena in Jupiter (Fletcher et al. 2024).
JUICE is in a long cruise to Jupiter that includes three close flybys of the Earth. The first of these flybys occurred on August 20, 2024 with two more flybys planned for Sept. 2026 and January 2029. JANUS is a high-resolution camera that operates in the 340-1080 nm spectral range and will obtain the highest spatial resolution images of the mission (Palumbo et al. 2025). During the 2024 flyby, JANUS obtained a sequence of 20 nightside images over a narrow strip from Madagascar to Vietnam at a spatial resolution of 146-257 m, and from a distance of 9,807-17,476 km with typical exposure times of 25 to 36 ms. While these images did not result in detection of lightning, the images show distinct compact lights from city lights, intense and mild fires and lights from maritime traffic that demonstrate the potential for lightning investigations on Jupiter (Hueso et al., 2026).
Lightning in Jupiter is considered to be much more intense and powerful than on Earth, and has been imaged by every spacecraft that has approached the planet (e.g., Becker et al., 2020). JANUS will obtain images of Jupiter over 3.5 yrs including multiple surveys of lightning in the planet’s nightside at different spatial resolutions and with different time cadences. Jovian lightning originates at pressures higher than 3 atm and can be observed in regions where no apparent storms are visible in the upper clouds at around 500 mbar. The spatial distribution, energy released and overall lightning activity connects observations of the upper atmosphere, where clouds of ammonia ice make most of the observable clouds, with intense phenomena at the base of the weather layer at pressure levels of 4-7 bar, where water condenses and lightning most likely originates.
We show JANUS observations of Earth’s nightside and review similarities and differences between lightning on Earth and Jupiter. We summarize our planned investigation of lightning activity in Jupiter and show how these Earth observations help us determine the sensitivity of the instrument towards the characterization of lightning at Jupiter.
References
- Becker et al., Small lightning flashes from shallow clouds on Jupiter. Nature (2020).
- Fletcher et al. Jupiter Science Enabled by ESA’s Jupiter Icy Moons Explorer. Space Science Reviews (2023).
- Grasset et al. JUpiter ICy moons Explorer (JUICE): An ESA mission to orbit Ganymede and to characterise the Jupiter system. Planetary and Space Science (2013).
- Hueso et al., JANUS observations of Earth in preparation for its investigation of Jupiter’s atmosphere. Annales Geophysicae, in preparation (2026).
- Palumbo et al. The JANUS (Jovis Amorum ac Natorum Undique Scrutator) VIS-NIR Multi-Band Imager for the JUICE Mission, Space Science Reviews (2025).
How to cite: Hueso, R., Palumbo, P., Tubiana, C., Portyankina, G., Lara, L. M., Yair, Y., Haruyama, J., Sato, M., Yukihiro, T., Simon, A., Coustenis, A., Agostini, L., Luchetti, A., Penasa, L., Aboudan, A., Antuñano, A., Roatsch, T., Kersten, E., Matz, K.-D., and Patel, M. and the JANUS Earth flyby team:: Prospects for Lightning Detection on Jupiter using JANUS on the JUICE mission: Insights from JANUS Earth observations , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12136, https://doi.org/10.5194/egusphere-egu26-12136, 2026.
Uranus is an Ice Giant planet, a class of large, cold planets characterized by thick atmospheres and the absence of a well-defined solid surface. Hence, atmospheric processes are fundamental to understanding the planet’s physical and chemical environment. Atmospheric ionisation on Earth is driven by solar radiation and energetic particles, radioactive gases and Galactic Cosmic Rays (GCRs) [1]. GCR-induced ionisation is believed to be dominant on Uranus due to its distance from the Sun. In this work, we model the GCR air showers using CORSIKA8 Monte Carlo simulations [2] and calculate the vertical ionisation rate. We capture the variation of ionisation rates with geomagnetic latitude in a novel global map and, for the first time, present a quantitative comparison with ionospheric ionisation rates derived from parameters adopted from the literature. The results show GCR-induced ionisation in the lower stratosphere (peaking at ~104 Pa) to be around two orders of magnitude larger than ionospheric ionisation (<10-1 Pa), highlighting the significance of GCRs in Uranus’s atmosphere and raising questions about potential seasonal variability associated with solar-driven ionospheric processes.
The conditions in the lower stratosphere were carefully constrained, and with appropriate assumptions regarding steady-state conditions and dominant recombination mechanisms, the ion balance equation was solved to estimate the positive ion and electron number densities. Ion and electron densities peak at approximately the same altitude as the peak of GCR-induced ionisation with an upper limit of ~2×109 ions m-3 in the absence of aerosols, while the inclusion of aerosols leads to a difference between positive ion (~109 ions m-3) and electron densities (~108 electrons m-3). The electrical characteristics as well as cloud microphysics assumptions allow investigation of the possibility and nature of lightning activity expected on Uranus.
[1] Hillas, A. M. (1972). Cosmic rays (1st ed.). New York: Oxford ; New York : Pergamon Press.
[2] Gottowik, M. (2025). Corsika 8: A modern and universal framework for particle cascade simulations. arXiv preprint arXiv:2508.08755.
How to cite: Al-Khuraybi, O., Aplin, K., and Gambaruto, A.: Characterising Uranus’ Ionisation and Conductivity Profile, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15467, https://doi.org/10.5194/egusphere-egu26-15467, 2026.
Potential gradient (PG) is measured continuously at Xanthi, NE Greece, since 2011, along meteorological variables and, in the last years, also particulate matter (PM). We present here a 15-yr climatology of PG at the measurement site. 1-min values up to +/- 34 kV/m were measured. 1-hr and mean daily maximum (minimum) values were 10 kV/m (-12 kV/m) and 6 kV/m (-2 kV/m), respectively. The highest mean values were encountered during the winter months. PG was influenced by the local meteorology, specific humidity having the largest impact on PG values. Additionally, PG was influenced by lightning activity within 50-km from the site, as well as aerosol levels. PG was exhibiting some anticorrelation with PMK2.5, especially during the cloud-free summer months. This probably means that one or more of the following apply for Xanthi: PM has low hygroscopicity, the size of PM is small, the presence of PM is correlated with high ion concentrations, as there is a relatively high radon flux at the site. An increase of 20 μg/m³ in PM2.5 leads to a decrease of 100 V/m in PG. Regarding global events, it was observed that during two Sudden Stratospheric Warming (SSW) events, mean daily values of PG were consistently higher by what would be expected by the influence of local meteorology alone.
How to cite: Kourtidis, K., Karagioras, A., and Kosmadakis, I.: A 15-year climatology of Potential Gradient at a rural site in Southern Balkans, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1907, https://doi.org/10.5194/egusphere-egu26-1907, 2026.
Mineral dust influences radiation, clouds, and air quality, and can acquire electric charge through particle interactions and turbulent mixing. Observations of dust electrification at aircraft altitudes remain limited. Aircraft measurements provide a valuable opportunity to investigate how atmospheric electric fields respond to airborne dust under varying thermodynamic and aerosol conditions.
We analyse observations from the FAAM aircraft during flights sampling Saharan dust layers, to investigate electric field mill records associated with airborne dust regions. The electric field mill employed senses the ambient vertical electric field indirectly, but does not directly sample particles. It responds to electric fields induced by charged aerosols, the aircraft, and the surrounding atmosphere. Electric field measurements are analysed alongside co-located thermodynamic, wind, aerosol, and cloud observations, including ascent and descent profiles through dust plumes of varying intensity. In an intense dust case, the electric field signal strengthens as the aircraft approaches and enters the main dust layer at mid-tropospheric altitudes, coincident with decreasing relative humidity and enhanced aerosol loading. These results indicate that the electric field measurements are sensitive to electrically active dust layers aloft, providing new constraints on how dust charging evolves with altitude, humidity, and particle loading.
How to cite: Alblooshi, S., Nicoll, K., Harrison, G., and Ryder, C.: Electric Field Responses to Airborne Dust in FAAM Aircraft Measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14486, https://doi.org/10.5194/egusphere-egu26-14486, 2026.
In this presentation we describe a proof-of-concept study on the possibility of detecting high electric fields in the atmosphere e.g. around thunderstorms, using remote sensing techniques. Current methods to measure electric field profiles through the atmosphere rely on radiosondes or aircraft operating in conditions where the instrument is prone to damage or give unreliable results. We are investigating the feasibility of an alternative approach, which exploits the sensitivity of certain molecules to their electrical environment through the so-called Stark effect, whereby certain spectral lines are shifted in response to an external electric field. This has the potential for the measurement of high electric fields above thunderstorms, although it does present a number of challenges . In our study, we have been using radiative transfer models to simulate the effect of electric fields (such as are typically found around thunderstorm clouds) on atmospheric spectra, looking in particular at THz wavelengths and focusing on selected candidate spectral lines of HDO. Here, we will present our latest results.
How to cite: Waterfall, A., Cox, C., and McCormack, E.: Towards the Remote Sensing of Electric Fields in the Atmosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18193, https://doi.org/10.5194/egusphere-egu26-18193, 2026.
Long-term measurements of the atmospheric electric field, measured as the potential gradient (PG), were obtained at Lerwick Observatory (Shetland Isles), UK, from 1925 to 1984, and provide a unique resource for studying links between atmospheric electricity, the global electric circuit (GEC), and climate variability. Most of these historical observations were originally made as handwritten or printed records, limiting their accessibility for modern analysis. In this project, we have undertaken a comprehensive digitization of the Lerwick PG dataset, at hourly resolution, by combining contributions from a citizen science platform and various AI tools.
The earliest handwritten records, made from 1927–1956, were digitized through the Zooniverse citizen science platform by engaging volunteers in transcribing data. To digitize the later records, from 1957–1984, which are mainly printed and scanned tables, we utilized AI-based optical character recognition (OCR) tools from several software packages. An essential part of the transcription the use of multiple validation steps to assess and correct errors introduced by both the AI-based tools and the citizen science activity. By these techniques, we optimised the effectiveness of the digitisation to provide the most scientifically useful dataset.
This work presents a summary of the digitized historical dataset from Lerwick and provides insights into the reliability and limitations of AI-assisted digitization of scientific archives. The resulting new dataset generated will underpin modern investigations into long-term trends in atmospheric electricity and its connection to climate processes.
How to cite: Mkrtchyan, H., Nicoll, K., and Harrison, G.: Combining human and AI approaches for effective digitization of historical atmospheric electricity records, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14791, https://doi.org/10.5194/egusphere-egu26-14791, 2026.
Lightning is a fundamental part of the Earth's climate system, occurring worldwide at a rate of about 45 flashes per second on average. It has recently been recognized as an Essential Climate Variable and serves as an indicator of thermodynamic instability.
In the past years, lighting climatologies have been derived for various regions worldwide. However, this does not yet include vast parts of Southwest Asia, i.e., the broader region encompassing the Eastern Mediterranean, Black Sea, Caspian Sea, Red Sea, and Persian Gulf, as well as the Middle East (Anatolia, Levant, and Arabian Peninsula) and the Caucasus regions. Unlike the tropical lightning hotspots (e.g., the Congo Basin or Venezuela), this area is often overlooked in global lightning studies due to its lower overall flash density. Despite its low average flash rates, the region displays complex and rather unique interactions between distinct atmospheric circulation patterns and local thermodynamic processes in the atmosphere.
This study aims to unravel the complex factors that control lightning activity in a transitional zone where these different physical processes intersect. Specifically, a reliable lightning climatology for Southwest Asia and the neighboring regions is developed that combines data from available space missions and different ground-based detection networks for the period 2017-2023. The resulting spatial patterns of lightning flash density, along with their seasonal and inter-annual variability, contribute to a better understanding of the effects of orography, land-sea configuration, land cover, and prevailing regional weather patterns on lightning. In order to attribute the obtained activity patterns to specific thermodynamic conditions and aerosol-cloud interactions that sustain electrification even in areas with limited moisture availability, atmospheric reanalysis data are employed with a focus on cloud properties.
How to cite: Karapetyan, G., Donner, R. V., Mkrtchyan, H., and Aslanyan, D.: Filling the Gap: Lightning Climatology of Southwest Asia, Northeast Africa, and the Eastern Mediterranean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15056, https://doi.org/10.5194/egusphere-egu26-15056, 2026.
Lightning activity is influenced by both aerosols and cloud microphysics, particularly ice formation and charge separation. While aerosols can greatly modify microphysical processes via cloud condensation nuclei (CCN), the global relationship between CCN loading and lightning remains unclear. In this study, we used global lightning stroke density, aerosol, and microphysics data to investigate how CCN can alter lightning through microphysical pathways across different regions. Our preliminary analysis reveals a robust CCN-lightning relationship, with lightning peaks at moderate CCN (400-600 cm-3) and decreases at both lower and higher concentrations. A metric used to quantify the microphysical impact is called ‘glaciation ratio (GR)’, which is defined as the ratio between cloud-ice water path and the total water path. We identify distinct continental (high CCN, high GR) and marine (moderate CCN, moderate GR) regimes. Analysis of glaciation ratio shows synergistic effects: optimal lightning requires both appropriate CCN loading and efficient cloud glaciation. Our findings show that more aerosols do not always mean more lightning. However, the hypothesis proposed is that excess CCN diminishes convection through reduced droplet growth, while low CCN suppresses electrification due to the efficient warm-rain process. Our analysis shows that CCN impacts on the observed lightning activity are regime-dependent, with cloud glaciation playing a central role in determining whether CCN enhances or suppresses electrification.
How to cite: Waman, D., Nassar, A., and Hoose, C.: Regime-dependent Impacts of CCN and Cloud Glaciation on Global Lightning Activity , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3745, https://doi.org/10.5194/egusphere-egu26-3745, 2026.
How is lightning triggered on the microscale? Despite decades of research, this question remains unanswered [1]. In our experiment, we use optical tweezers to gain a better understanding of the microscale physics of electric charging and discharging by levitating individual SiO2 particles in the micrometer size range and observing 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]. Using two-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. This new approach lets us watch, in real time, how a micron-scale airborne particle gains and loses charge, observing its electric evolution all the way from the neutral state to the point where it undergoes electric discharge. 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.
Figure 1: Time vs. electric charge curve of a single SiO2 sphere (d = 0.69 µm) showing spontaneous discharges.
This project has received funding from the European Research Council (ERC) under the European Union’s Starting Grant (A. Stoellner, I.C.D. Lenton & S.R. Waitukaitis received funding from ERC No. 949120, C. Muller received funding from ERC No. 805041).
[1] Dwyer, J. R., & Uman, M. A. (2014), Physics Reports, 534(4), 147–241.
[2] Ricci, F. et al. (2019), Nano Letters 19, 6711.
[3] Stoellner, A. et al. (2025), Phys. Rev. Lett. 135(21), 218202.
How to cite: Stoellner, A., Lenton, I., Muller, C., and Waitukaitis, S.: Measuring spontaneous discharges of individual aerosol particles with optical tweezers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5136, https://doi.org/10.5194/egusphere-egu26-5136, 2026.
Lightning serves as a fundamental indicator of convective intensity and an important mediator of atmospheric dynamics. Accurately modeling the potential for lightning occurrence is essential for understanding storm electrification and improving short-range forecasting. The Lightning Potential Index (LPI) is a physically based diagnostic parameter that quantifies the potential for charge generation within convective clouds. It combines model-resolved updraft velocity and precipitating ice content, thereby directly representing the mechanisms responsible for non-inductive charging (Yair et al., 2010). In contrast, thermodynamic indices such as the K-Index (KI) and Convective Available Potential Energy (CAPE) reflect the environmental instability and likelihood of convection, but lack an explicit representation of microphysical electrification processes (Peppler, 1988). Additionally, accumulated precipitation serves as a proxy for the integrated intensity of the storm systems. In this study, we evaluate the skill of this suite of atmospheric predictors - meaning LPI, KI, CAPE, and precipitation – all computed from WRF ensemble simulations, in reproducing observed lightning activity over the Eastern Mediterranean. Five case studies were selected, representing different synoptic conditions in winter. A comprehensive processing pipeline was developed to co-register model outputs and ground-based lightning detections from the ENTLN network onto a uniform 4 × 4 km grid and 3-hour temporal intervals. Spatially, all parameters were averaged per grid cell. Temporally, precipitation was summed, while other variables (LPI, KI, CAPE) were averaged over each period. All datasets were smoothed with a Gaussian kernel to reduce spatial noise and enable direct comparison across domains. Preliminary analyses indicate that thermodynamic indices and accumulated precipitation exhibit broad spatial footprints, significantly overestimating the areal extent of lightning activity. While LPI also displays a tendency towards broader coverage than observed, it demonstrates the highest degree of spatial localization among the examined parameters. To further quantify predictive skill, we employ a machine learning approach based on Random Forest algorithm. The spatial model matrices are decomposed into discrete single-cell vectors, utilizing the full suite of parameters. These features are used to classify the binary occurrence of lightning (presence/absence), independent of flash multiplicity, establishing a robust data-driven mapping between storm microphysics and lightning probability.
References
- Y, B. Lynn, C. Price, V. Kotroni, K. Lagouvardos, E. Morin, A. Mugnai, and M. d. C. Llasat (2010), Predicting the potential for lightning activity in Mediterranean storms based on the Weather Research and Forecasting (WRF) model dynamic and microphysical fields, J. Geophys. Res., 115, D04205, doi:10.1029/2008JD010868.
- Peppler, R. A. (1988). A review of static stability indices and related thermodynamic parameters. ISWS Miscellaneous Publication MP-104.
How to cite: Yair, Y., Pitlik, K., Price, C., Korzets, M., Lerman, C., Alisse, J., Lynn, B., and Galili, B.: Predicting Eastern Mediterranean lightning: evaluating microphysical and thermodynamic indices using a machine learning approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8984, https://doi.org/10.5194/egusphere-egu26-8984, 2026.
Tropospheric lightnings are fundamental sources of natural ultra-wide band (UWB) electromagnetic waves, utilised in various fields of exploration of the upper atmosphere and the plasma environment. Lightnings are observed by numerous detection systems, deployed as ground networks or operated on satellites/cubesats, all exhibiting specific limitations in detection efficiency (DE), sensibility, spatial coverage, and overall performance.
We have compared the flash database of the LI optical experiment onboard the Meteosat Third Generation (MTG) geostationary satellite (0° longitude, operational since July 2024) with the ground-based WWLLN VLF stroke data set in the period of July 2024 – May 2025, within the FoV of the MTG sensors. For that purpose the necessary correction of the location and time coordinates was first performed in the MTG data set. This step sets the spacecraft observation time backwards with the propagation time (approx. 120-140 ms), and also decreases the latitude and longitude coordinates towards the sub-satellite line due to the finite altitude of the observed optical phenomenon at cloud top.
The ratio of the detected events, binned in a 1° by 1° raster in the African continental region, varying somewhat geographically, falls in the remarkable range of several hundreds. This difference can be explained partly by the known poor DE of the WWLLN over Africa, and by the fact that MTG LI detects total lightning (cloud-to-ground and intracloud/cloud-to-cloud), while WWLLN primarily detects strong CGs. A one-by-one matching of MTG flashes with detected WWLLN strokes, applying temporal and spatial windowing (±330 ms, and <25 km, respectively) was also completed. This analysis exhibited clear asymmetry in the distribution of the time offsets between matching events (time stamps of MTG flashes seem to precede the corresponding WWLLN time values by tens of ms). The distribution of spatial separation of matching pairs has a maximum at 8 km. Due to the reasonably strict conditions used in matching pair selection, the overwhelming number of detected lightnings in the MTG LI data set is not seen in the one-by-one comparison: 97.3 % of WWLLN to MTG LI matchings are single event pairs, a multiplicity factor of 2 is represented only by 2.5 % of matched events.
How to cite: Steinbach, P., Bozóki, T., Németh, K., and Lichtenberger, J.: Comparison study on the MTG LI and WWLLN lightning data sets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17570, https://doi.org/10.5194/egusphere-egu26-17570, 2026.
The development of satellite-based lightning detection has enabled continuous monitoring of total lightning activity over a widespread area. However, in order to properly interpret satellite-derived lightning data, it is important to compare them with existing ground-based lightning detection networks. This study uses satellite observations from Meteosat Third Generation Lightning Imager (MTG LI) and ground-based measurements from the Low-frequency International Lightning Detection Network (LINET). A total of ten hail-producing convective cases over Croatia and neighbouring countries were selected for the period from July 2024 to July 2025.
The main goal of this research is to compare lightning detection from MTG LI and LINET during different phases of convective storms with hail. Therefore, both spatial and temporal differences in lightning detection before, during and after hail occurrence were analysed. In addition, temporal changes in lightning properties were observed, including flash duration, area and radiance, as well as lightning type, height and current amplitude. To assess the role of storm intensity in the observed differences, the convective mode was determined for selected storms.
The results show a good spatial agreement between the two measurement systems and a similar temporal evolution of observed lightning activity. However, the number of detected lightning flashes strongly depends on individual storm characteristics, which influence the detection efficiency of both systems. A decrease in flash area, duration and radiance was observed shortly before and during hailfall.
How to cite: Telisman Prtenjak, M., Simunec, D., and Strelec Mahovic, N.: Comparison of lightning detection from satellite and ground-based measurements during selected cases of convection with hail , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21267, https://doi.org/10.5194/egusphere-egu26-21267, 2026.
Schumann resonances (SR) correspond to the around-the-globe eigenmodes of the thin spherical shell bounded by the Earth’s surface and the lower ionosphere. This system forms a waveguide for extremely low frequency (ELF, 3 Hz - 5 kHz) electromagnetic waves. The SR modes are primarily excited by the quasi continuous lightning activity worldwide. The lowest SR modes are at ~7.8 Hz, ~14.1 Hz, ~20 Hz. The actual peak frequencies and amplitudes of the spectrum depend on both the distribution and intensity of the global thunderstorm activity. SR parameters also carry information on the electrical state of the boundary layers of the waveguide and so they are capable of indicating significant and extensive changes in the vertical profile of the atmospheric electric conductivity. ELF-band spectra of the horizontal magnetic and vertical electric field components are the most suitable for studying these dependencies, but only if the ambient noise does not mask the otherwise rather weak SR signal. In this contribution, a methodology is introduced to determine the signal to noise ratio (SNR) near the low end of the ELF-band that includes the most often detectable lowest SR modes. The concept is based on fitting a model SR spectrum to the measured one and so separating the SR signal from the other components considered further as noise. This approach is demonstrated on the time series recorded at the ELF-band monitoring sites of the HUN-REN Institute of Earth Science and Space Research in the Széchenyi István Geophysical Observatory near Nagycenk Hungary (NCK, 16.72 E, 47.63 N) and in the Jeli Arboretum near Kám, Hungary (JAR, 16.89 E, 47.08 N). The same analysis can be made on any similar record. Practical aspects of setting up an empirical threshold in the SNR to exclude or include data in SR-based studies are discussed in the light of the presented experiences.
How to cite: Reichardt, A. B., Atta, J., and Bór, J.: Towards quantifying the suitability of ELF-band radio observations for Schumann-resonance research, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6764, https://doi.org/10.5194/egusphere-egu26-6764, 2026.
Continuing current (CC) is a slowly varying lightning current that can follow a return stroke (RS) in cloud‐to‐ground lightning flashes and typically lasts from a few milliseconds to several hundred milliseconds. The necessary conditions and generation mechanism of CC formation have been studied for decades, motivated by the increased risk of physical lightning damage due to the long‐lasting current and large charge transfers. Nowadays, there is a growing interest in the study of CC, mainly because of the important role it plays in the natural ignition of forest fires. The Krakow ELF group operates a pair of broadband magnetic antenna (sampling frequency: 3004.81 Hz, antenna bandwidth: 0.02 Hz – 1.1 kHz) in an electromagnetically very quiet environment in Hylaty, south-eastern Poland, which is very suitable for the recording of CCs. In this contribution, we introduce our semi-automated procedure for detecting and characterizing CCs in this measurement data and describe some characteristics of the long CCs (>40 ms) identified by our method on three selected days (3-5 July, 2025). Our algorithm first searches for peaks in the magnetic data that represent the ELF manifestation of RSs, then estimates the beginning and end of the waveform based on classic signal processing techniques. The time passed between the RS peak and the end of the waveform is considered to be the CC duration. In order to increase the reliability of the data system, we manually discard ambiguous cases and correct the estimated CC durations. Over the three selected days, a total of 7,052 RSs have been detected, of which 349 (~5%) were followed by a clear and long lasting CC signature. 90% of the CCs were observed in the daytime, 36.1% of them lasted longer than 100 ms, but only 6.6%/0.6% lasted longer than 200/300 ms. Part of the CCs can be well described as an exponential decay, but there are also a number of more complicated waveforms with M-component signatures and prolonged, slightly fluctuating parts. Interestingly, in approximately 5% of the cases, the RS is preceded by some initial activity (current flow) lasting longer than 10 ms. Next, we plan to use WWLLN/ENTLN and MTG data to automatically identify the source lightning discharge of the detected events, as well as to employ machine learning techniques to make the CC detection more effective. We expect that our method will enable us to study lightning CCs in a much larger data set than ever before.
How to cite: Bozoki, T., Mlynarczyk, J., and Horvath, A.: Characteristics of Long Continuing Currents Observed in Broadband ELF Measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12870, https://doi.org/10.5194/egusphere-egu26-12870, 2026.
LOFAR has been used to image lightning initiation, leader stepping, dart leaders, needles, and more
with sub-meter resolution and high sensitivity. Over the last few years LOFAR has been almost
completely rebuilt from the ground-up into LOFAR2.0. Apart from the physical antennas, nearly all of
the analog and digital processing chains have been completely replaced and upgraded. In addition to
greater bit-depth and better amplifiers, a new automatic white-rabbit based time calibration will allow
for easier and faster data processing. Combined with a faster network that allows for less down-time,
more lightning flashes per thunderstorm can be observed and mapped with high precision. LOFAR2.0
will also have triple the number of processing pipelines, thus allowing for observing simultaneously
with both the low-band antennas (10-90 MHz) and the high-band antennas (110-240 MHz). The higher
frequencies will allow for significantly higher resolution, perhaps even allowing for the resolving of the
sub-meter widths of streamer bursts during lightning initiation. This poster will discuss some of the
new and still-planned upgrades to LOFAR system, as well as our various imaging techniques such as
our impulsive imager and near-field beamforming (TRI-D and ATRI-D).
How to cite: Hare, B., Cummer, S., Dwyer, J., Liu, N., Lourens, M., Scholten, O., Sterpka, C., Turekova, P., Wu, B., and Nl, A.: Using the new LOFAR2.0 upgrade for lightning imaging, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9296, https://doi.org/10.5194/egusphere-egu26-9296, 2026.
Lightning is a key manifestation of severe convective weather and poses a significant natural hazard to power infrastructure, particularly overhead transmission lines and towers. However, lightning occurrence is governed by the combination of multiple atmospheric and cloud-scale processes. Existing studies largely rely on correlation-based analyses, which provide limited insight into the temporal roles of different precursors prior to lightning.
In this study, we develop an event-driven, multi-scale causal analysis framework based on a large set of real-world lightning events over the UK. Each lightning event is temporally aligned with its preceding atmospheric evolution, combining hourly ERA5 reanalysis variables, including temperature, moisture, and precipitation, with high-temporal-resolution satellite-derived cloud-top height observations. Causal discovery methods are applied to identify lagged relationships at the hourly scale, while robust lag analysis is used to characterise short-timescale cloud-top evolution. The analysis reveals that lightning events are commonly preceded by physically consistent, ordered triggering processes. As a case study, we discuss the implications for power infrastructure risks. The proposed framework provides a data-driven and physically interpretable basis for assessing lightning-related risks to transmission networks and other assets.
How to cite: Wang, X., He, X., Ali, A., Fullekrug, M., and Gu, C.: Multi-scale causal analysis of processes causing lightning and implications to Energy infrastructure, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20775, https://doi.org/10.5194/egusphere-egu26-20775, 2026.
In this study we present, to the best of our knowledge, the first three-dimensional (3D) reconstruction of an upward lightning flash using combined very high frequency (VHF) interferometric and high-speed camera (HSC) observations. Based on this reconstruction, we estimate the 3D velocities of different pulse fronts along the channel branches. Comparable 3D reconstructions have previously been reported for downward lightning flashes [1].
The Mt. Säntis Lightning Research Facility [2], located in the Appenzell region of Eastern Switzerland, features an electric field and current measurement system, as well as a Phantom HSC situated at a distance of 5 km from the namesake mountaintop tower. Additionally, during the summer 2021 experimental campaign, a VHF interferometer (IFM) belonging to New Mexico Tech was installed at the base of Mt. Säntis, 2 km away from the tower. The HSC operated at 24,000 fps and the IFM at 200 MS/s, corresponding to respective time resolutions of 42 μs and 5 ns. The spatial resolutions of the HSC and IFM were 512 x 512 pixels and 0.1°, respectively, both corresponding to ~3 m at the location of the tower tip. These two instruments were used in combination to reconstruct in three dimensions the bottom ~600 m of an upward negative flash that initiated from the Säntis Tower on July 30, 2021, at 15:38:10 UTC. This particular flash featured numerous “mixed-mode” pulses superimposed on the initial continuous current (ICC), in addition to the standard dart leader–return stroke sequences, identified as such from their current and E-field waveforms. The ICC pulses propagated downward along 4+ different visible branches; altitude change rates averaged -5.6 ± 2.0 x 106 m/s and were observed to decrease slightly as the pulse fronts approached the strike point. 3D speeds of ~2 x 107 m/s were observed, punctuated by spikes (spaced on the order of 10 μs apart) at times exceeding 1e8 m/s, indicative of step-like behaviour. Such an analysis of ICC pulse velocities is heretofore absent in the literature and lends itself to an improved understanding of leader dynamics and charge transfer mechanisms in upward lightning.
References:
[1] Li, Y., Qiu, S., Shi, L., Huang, Z., Wang, T., Duan, Y., 2017. Three‐Dimensional Reconstruction of Cloud‐to‐Ground Lightning Using High‐Speed Video and VHF Broadband Interferometer. JGR Atmospheres 122. https://doi.org/10.1002/2017JD027214
[2] Rachidi, F., Rubinstein, M., 2022. Säntis lightning research facility: a summary of the first ten years and future outlook. Elektrotech. Inftech. 139, 379–394. https://doi.org/10.1007/s00502-022-01031-2
How to cite: Oregel-Chaumont, T., Kasparian, J., Stanley, M., Rison, W., Šunjerga, A., Rubinstein, M., and Rachidi, F.: Combining VHF and optical observations to reconstruct an upward flash, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10290, https://doi.org/10.5194/egusphere-egu26-10290, 2026.
It is essential to clearly separate pulse noise from lightning emissions to detect lightning on planets. Therefore, LAC (lightning and airglow camera) onboard Akatsuki spacecraft sacrificed high spatial resolution by using 32 pixels, instead opting for a high photometric sampling frequency of 20 kHz. This design allows smooth capture of brightness fluctuations, even for short-duration phenomena like terrestrial lightning. Furthermore, based on discharge experiments using CO2, the primary component of Venus's atmosphere, a narrow-band filter for the most prominent oxygen atomic emission line (777 nm) was installed. Sensitivity was set, referencing results from satellite observations on Earth, to detect emissions on Venus even when it is in close approach, down to levels less than one-tenth of those seen in terrestrial lightning. Although the extended elliptical orbit of Akatsuki and its longer period reduced the LAC observation time—which activates only during Venus's shadow—to about one-twentieth of the original planned rate, observations commenced successfully in 2016. However, for the first four years after the start of observations, only cosmic ray pulses were recorded; not a single light curve resembling lightning was obtained. Finally, in March 2020, a single event was triggered and recorded. Its duration was approximately 200 milliseconds, far longer than the typical few milliseconds of Earth lightning. This duration cannot rule out the possibility of a meteor (fireball). However, calculating the probability of a meteor of that brightness being observed by LAC based on the observed luminosity yielded a probability between 0.1% and 8.3%. Furthermore, considering that 200 milliseconds is short for a meteor, the probability of it being a meteor becomes even smaller. On the other hand, some Earth lightning events observed in Earth orbit also have durations exceeding several hundred milliseconds, similar to this LAC event. Based on these facts, while we cannot completely rule out the possibility of it being a meteor or meteorite fall, we believe it is highly likely to be lightning discharge luminescence. Moving forward, we intend to explore the significance of the lightning information obtained on Venus by using the light curve obtained by Akatsuki as a clue to investigate the meteorological conditions under which similar terrestrial lightning occurs. Simultaneously, using the LAC waveform as a reference, we are developing ground-based telescope measurements of lightning emissions utilizing the latest high-speed imaging observation equipment.
How to cite: Takahashi, Y., Ono, T., Lorenz, R., Sato, M., Imai, M., Yair, Y., and Fischer, G.: Lightning detection on planets using spacecraft and grond-based telescope, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21100, https://doi.org/10.5194/egusphere-egu26-21100, 2026.
The summer season of 2023 brought to Lomnický štít (Slovakia) one of the strongest gamma-ray glows (GrGs) ever recorded. As Lomnický štít is a unique observation point for GrGs, we equipped the observatory with multiple detectors in the frame of the CRREAT project. In addition to the existing Neutron monitor, SEVAN detector, and Boltek electric field mill, we also installed an RT-56 large NaI(Tl) gamma-ray spectrometer, a small Geodos gamma-ray spectrometer, silicon mosaic detectors, Timepix detectors, PIN diode detectors, a camera, and additional Boltek electric field mills. On 14 June 2023, a thunderstorm cell formed in the vicinity of the observatory and exhibited a strong electric field. This field caused a strong GrG detected by all of the above-mentioned ionizing radiation detectors, standing out as our finest recorded event to date, enriched by the deployment of an unprecedented set of advanced instruments. The duration of the GrG was at least five minutes and was ended by a discharge very close to the count rate's peak of a typical Gaussian curve. The thunderstorm cell remained active and produced two more detected GrGs. One of them also ended with a discharge.
How to cite: Šlegl, J., Kákona, M., Langer, R., Strhárský, I., Chum, J., Lužová, M., Velyčková, H., Sommer, M., Ambrožová, I., and Ploc, O.: An exceptionally strong gamma-ray glow at Lomnický štít observed by an unprecedented number of ionizing radiation sensors, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12611, https://doi.org/10.5194/egusphere-egu26-12611, 2026.
From the discoveries by the Airborne Lightning Observatory for FEGS and TGFs (ALOFT), we know that thunderclouds can emit gamma-rays for hours over very large distances. Marisaldi et al. (2024) reported observations of numerous glowing regions, each containing several individual glows, as the aircraft passed over active thunderclouds. Overall, ALOFT detected more than 500 glows, showing a wide variety of time profiles, including glows with a gradual decay and those with a very sharp decrease in gamma-ray flux after reaching the peak intensity. Making use of the combination of instruments onboard ALOFT, as well as ground-based sensors, we explore the termination of gamma-ray glows detected by ALOFT. In this study, we focus on glows with a very fast decrease in flux (reduction by >50% in <20 ms) and explore which types of electric discharges are associated with this fast termination.
References:
Marisaldi, M. et al. (2024), Highly dynamic gamma-ray emissions are common in tropical thunderclouds, Nature, 634, 57, doi.org/10.1038/s41586-024-07936-6
How to cite: Bjørge-Engeland, I., Marisaldi, M., Østgaard, N., Mezentsev, A., Fuglestad, A., Cummer, S., Pu, Y., Quick, M., and Christian, H.: Discharge processes associated with fast decaying gamma-ray glows observed during the ALOFT aircraft campaign, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19365, https://doi.org/10.5194/egusphere-egu26-19365, 2026.
Recent data from the ALOFT flight campaign have confirmed the lightning activity and high energy particle acceleration interconnection. The results comprised the discovery of a large fraction of low-brightness Terrestrial Gamma-ray Flashes (TGFs), signifying that the bright flashes observed from space account for only a small fraction of these events. Many of these weak TGFs, undetectable from space, are associated with a prominent 337.1 nm optical pulse and differ from those detected from space by the lack of 777.4 nm dominated lightning discharges [Mezentsev et al. 2025]. Brightness down to 1012 photons at a source reference altitude of 15 km have been observed and there is no theoretical reason that opposes the existence of dimmer TGFs [Bjørge-Engeland et al. 2024; Fuglestad et al. 2025].
Although detection of individual events would be prevented due to instrument sensitivity, this project aims to tackle this obstacle by stacking the gamma-ray signals in timeframes prior to the emergence of blue dominated lightning discharges. If a substantial population of dim TGFs below the sensitivity threshold for ALOFT exists, it should appear as an enhancement in the cumulated gamma-ray signal.
This presentation focus on the stacking analysis of the gamma-ray data detected by ALOFT in association with the blue dominated lightning discharges. We will present the methodology, the data selection strategy and the preliminary results.
References:
A. Mezentsev et al. (2025). New Class of Gamma-Ray Flashes Indicate Gamma Glow Rest through Fast Streamer Discharge. https://doi.org/10.5194/egusphere-egu25-15838
I. Bjørge-Engeland et al. (2024). Evidence of a New Population of Weak Terrestrial Gamma—Ray Flashes Observed from Aircraft Altitude. Geophysical Research Letters, 51, https://doi.org/10.1029/2024GL110395
A. Fuglestad et al. (2025). The source brightness distribution of Terrestrial Gamma-ray Flashes from the ALOFT flight campaign. Submitted to JGR: Atmospheres
How to cite: Khan, R., Marisaldi, M., Bjørge-Engeland, I., Østgaard, N., and Quick, M.: Gamma-ray production associated with blue dominated lightning discharges in glowing thunderclouds observed by ALOFT, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21097, https://doi.org/10.5194/egusphere-egu26-21097, 2026.
Observations over recent decades show weak, and in some regions non-positive, indications of ozone recovery in the lower stratosphere, in contrast with the clearer recovery observed at higher altitudes. The processes contributing to this behaviour remain insufficiently constrained, particularly where variability is driven by episodic and spatially confined phenomena. Better constraining such processes is essential for a more complete understanding of the ongoing evolution of the ozone layer.
In this context, we investigate the potential influence of thunderstorm-related electrical discharges in the blue spectral range, also known as blue corona discharges, as a source of localized perturbations to lower-stratospheric ozone. These blue events with strong 337 nm emissions, detected by the Atmosphere Space Interactions Monitor (ASIM), are typically associated with vigorous convection and may generate reactive nitrogen and hydrogen species capable of modifying the local chemical environment.
We apply a co-location framework that combines ASIM detections with coincident limb-sounding ozone observations in the vicinity of convective systems exhibiting blue corona discharges. Initial case studies demonstrate the feasibility of this approach and reveal signatures consistent with localized ozone variability in the lower stratosphere.
Although the current number of events coincident with limb-sounding measurements does not yet permit statistically robust attribution, the results motivate the expansion of the event catalogue and the inclusion of additional observational constraints. Taken together, these findings highlight blue corona discharges as a potentially under-characterized process that may contribute to small-scale variability and regionally limited weaknesses in lower-stratospheric ozone recovery.
How to cite: Rose, K., Li, D., Chanrion, O., Neubert, T., Marisaldi, M., Gordillo-Vazquez, F. J., and Dekemper, E.: Investigating the Influence of Blue Corona Discharges on Lower-Stratospheric Ozone Variability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3818, https://doi.org/10.5194/egusphere-egu26-3818, 2026.
Thunderstorms produce high-energy radiation events such as Terrestrial gamma ray flashes (TGFs) and Gamma ray Glows (GRGs) via bremsstrahlung during the acceleration of runaway electrons to relativistic energies. Although TGFs and GRGs are believed to originate from the same physical process (relativistic runaway electron avalanche (RREA)), TGFs are intense sub-millisecond bursts of X-rays, while GRGs are less intense, long-lasting X-rays emissions.
Several balloon flight campaigns are being prepared to observe and better understand these energetic phenomena such as Strateole-2 and OREO funded by the French Space Agency (CNES). Strateole-2 is a stratospheric balloon campaign using superpressure balloons flying for several months between 18 and 20 km in the intertropical region (planned for the end of 2026). OREO is a lightweight balloon project aiming to launch several radiosondes directly into thunderstorms to probe in-situ high-energy emissions associated with the electrical activity.
In order to participate in these projects a dedicated instrument named XStorm has been developed [Pallu, et al., JGR, 128, e2023JD039180, 2023, https://doi.org/10.1029/2023JD039180] with a view to perform in-situ and remote measurements. XStorm is a lightweight gamma-ray spectrometer its conception allow us to detect gamma ray glows and TGFs near the sources.
In addition, XStorm contributes to a new ground-based measurement campaign that involves installing it at key positions to detect and analyze TGFs as well as GRGs.
In this contribution, we present the XStorm detector, detailing its electronic architecture, operational principles, and performances, as well as the campaigns in which it will be used.
How to cite: Aziz, C.: XStorm: a Lightweight Gamma-ray Spectrometer Designed to Detect Terrestrial Gamma ray Flashes and Glows, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21751, https://doi.org/10.5194/egusphere-egu26-21751, 2026.
The UHU experiment (uhu.epss.hu) was conducted on the International Space Station (ISS) from 26 June to 14 July, 2025 to observe lightning activity and transient luminous events (TLEs) from space using a commercial color video camera. Several months before the mission, a call was issued seeking contribution to this experiment in the form of ground-based optical observations. One aim of the supporting ground campaign was to increase the chance of capturing one or more TLE from space and from the ground simultaneously, and use the respective images to quantify the effect of different propagation through the atmosphere on the recorded color and brightness distribution of the events. Although simultaneous observation of TLEs was not achieved eventually during the campaign, the attempt showed the currently already significant potential of the community of observers in supporting scientific missions targeting optical observations on a global scope. The result that TLEs were observed by contributors above thunderstorms which were also marked for the astronauts on the ISS as possible targets, validates the concept of the open call. The campaign has also provided useful experience that can be utilized in similar calls in the future to further increase the effectiveness of such activities and the scientific value of the collected observations. In this contribution, the preliminary results of the UHU ground-based optical observation campaign are summarised and the gained experiences are presented.
How to cite: Bór, J. and Yair, Y.: The contribution of citizen observers to the UHU lightning and TLE observation campaign on the International Space Station in 2025, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6579, https://doi.org/10.5194/egusphere-egu26-6579, 2026.
Gamma-ray glows are persistent (seconds to minutes) gamma-ray emissions from thunderclouds associated to intense large-scale electric fields. Results from the ALOFT flight campaign in 2023 over Florida and the Gulf of Mexico [1,2] have shown that tropical thunderclouds can glow in gamma-rays for hours and over thousands of square kilometres, pointing at particle acceleration as a fundamental and ubiquitous phenomenon in thundercloud electrodynamics, likewise cloud electrification and lightning discharge. Moreover, ALOFT measurements evidence a significant intrinsic time variability of gamma-ray glows, likely matching the dynamics of large scale thundercloud electric fields. Despite earlier attempts, there is no direct measurement of gamma-ray glow spatial extent. With the ENLIGHTEN project we have the ambition to measure directly the spatial extent of glows in gamma-rays and their spatio-temporal evolution. We will use diverse gamma-ray imaging systems hosted onboard a high-altitude aircraft from NASA flying over active thunderclouds. The ENLIGHTEN flight campaign is currently scheduled for July 2028. Here we present the preliminary design of the gamma-ray imagers and their expected performance based on Monte Carlo simulations informed by the ALOFT gamma-ray glow measurements.
[1] Lang, T. J., et al., 2025: Hunting for Gamma Rays above Thunderstorms: The ALOFT Campaign. Bull. Amer. Meteorol. Soc., https://doi.org/10.1175/BAMS-D-24-0060.1.
[2] Marisaldi, M., et al., 2024: Highly dynamic gamma-ray emissions are common in tropical thunderclouds. Nature 634, https://doi.org:10.1038/s41586-024-07936-6
How to cite: Marisaldi, M., Sarria, D., Grove, E., Shy, D., Mezentsev, A., Lehtinen, N., Østgaard, N., and Lang, T.: Imaging gamma-ray glows, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10184, https://doi.org/10.5194/egusphere-egu26-10184, 2026.
Since the 1953 Urey–Miller experiments, which produced organic precursors through electrical discharges in a simulated primordial Earth, electrical activity has been recognized as crucial for atmospheric evolution. Understanding planetary lightning, therefore, becomes essential when searching for life indicators across planets. Lightning activity has been confirmed through optical observations on Jupiter and Saturn, inferred electromagnetically on Uranus and Neptune, and theoretically predicted for Venus, Mars, and Titan. However, direct lightning detection faces significant challenges. Lightning typically originates in deep convective clouds, often below visible cloud layers where photons are heavily absorbed. This obscuration complicates direct optical detection from space. An alternative approach is to infer lighting by detecting transient luminous events (TLEs; sprites, jets, and Elves) which manifest in the upper atmosphere and produce distinctive optical and chemical signatures potentially more accessible to remote observation. Theoretical considerations based on a simple 1D quasi-electrostatic model (Yair et al., 2009; https://doi.org/10.1029/2008JE003311) predicted the possible occurrence of sprites on Jupiter, presuming that lightning discharges behave as on Earth (Kolamšová et al., 2023; https://doi.org/10.1038/s41467-023-38351-6). Recently, Giles et al. (2020; https://doi.org/10.1029/2020JE006659) reported the detection of unusual optical emissions in Juno images of Jupiter. Eleven bright transient flashes were observed by the spacecraft's UV instrument, with an average duration of 1.4 ms. They were located 260 km above the 1-bar level of Jupiter's atmosphere and were dominated by H2 emission. These observations are consistent with TLEs (possibly Elves). We present results from a three-dimensional quasi-electrostatic model of TLE generation developed by Haspel et al. (2022; https://doi.org/10.1016/j.jastp.2022.105853), which has been adapted to the Jovian atmospheric conditions for this study. The simulations investigate TLE inception volumes across different cloud configurations (parameters include the magnitude and spatial distribution of charge moments in deep H2O clouds at 5 bars, and shallow NH3 clouds at ~1 bar). Results demonstrate that sprites can form in Jupiter's mesosphere when lightning-induced quasi-electrostatic fields exceed the breakdown threshold appropriate for H₂-He mixtures at mesospheric pressures. The simulations reveal the altitude ranges and conditions where electric field-to-neutral density ratios reach critical values for electron avalanche inception and streamer development. Results from simulations of thunderstorms and TLE generation on Saturn will also be presented.
How to cite: Bar-Zeev, J., Yair, Y., Haspel, C., and Hochman, A.: Numerical simulations of TLE generation in the Jovian atmosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14016, https://doi.org/10.5194/egusphere-egu26-14016, 2026.
In 2023, the Airborne Lightning Observatory for FEGS and TGFs (ALOFT) flight campaign discovered a weaker population of TGFs previously undetected by satellite instruments. These weak TGFs were estimated to have source photons in the range of 10^12 to 10^16 (>100keV) at 15km reference altitude. [Bjørge-Engeland 2024; Fuglestad 2025]
By studying the population of weaker TGFs, it was found that a significant fraction of TGFs are associated with fast streamer discharges occurring in the gamma-ray-glowing portions of the thundercloud. These TGF distinguish themselves from the classical satellite-detected TGFs due to not having a prominent optical pulse in 777.4 nm associated with a lightning leader, having a short (about 1μs) rise time and being accompanied by a strong 337.1 nm optical pulse associated with streamers. Based on these observations, we hypothesize that these TGFs have a different initiation process than the “classical” leader-associated TGFs, and we therefore considered them a new type of TGF. [Mezentsev 2025]
Motivated by these findings, we search for gamma-ray signals associated to blue discharges detected by the Atmosphere-Space Interactions Monitor (ASIM) mission. ASIM offers global coverage and a much larger dataset of lightning discharges than ALOFT, at the price of a lower sensitivity to gamma-ray events. We hypothesize therefore that any gamma-ray signal associated to blue discharges in ASIM can be detected only by stacking gamma-ray data associated to a large number of blue discharges.
In this presentation, we show the results of a stacking analysis of gamma-ray data associated to blue dominated optical discharges detected by ASIM.
References:
I. Bjørge-Engeland et al. Evidence of a New Population of Weak Terrestrial Gamma—Ray Flashes Observed from Aircraft Altitude.
https://doi.org/10.1029/2024GL110395
A. Fuglestad et al. The source brightness distribution of Terrestrial Gamma-ray Flashes from the ALOFT flight campaign.
A. Mezentsev et al. New Class of Gamma-Ray Flashes Indicate Gamma Glow Rest through Fast Streamer Discharge.
https://doi.org/10.5194/egusphere-egu25-15838
How to cite: Fuglestad, A., Marisaldi, M., Mezentsev, A., Sarria, D., Østgaard, N., Neubert, T., and Gordillo-Vázquez, F.: Gamma-ray Stacking Analysis of Streamer Dominated Discharges detected by ASIM, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16950, https://doi.org/10.5194/egusphere-egu26-16950, 2026.
How to cite: Mezentsev, A., Østgaard, N., Marisaldi, M., Sarria, D., Lehtinen, N., Færder, Ø., Bjørge-Engeland, I., Cummer, S., Pu, Y., Quick, M., Lang, T., Pazos, M., and Stanley, M.: New class of TGF discovered during ALOFT 2023 campaign, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18708, https://doi.org/10.5194/egusphere-egu26-18708, 2026.
During the ALOFT flight campaign in July 2023, we discovered a population of weak TGFs in the range of 10^12 to 10^15 source photons in brightness (at a reference altitude of 15 km), not detectable by space-based instruments (such as ASIM on the ISS or Fermi) [Bjørge-Engeland 2024; Fuglestad 2025]. While extensive air showers (EAS) were previously discarded as a seeding source for space-observed TGFs (i.e., with source brightness above 10^16 photons) [Dwyer 2008; Carlson 2008], in principle, this does not exclude the possibility that the same mechanism could generate TGFs that are orders of magnitude weaker, like ALOFT’s weak TGFs. This hypothesis consists of EAS generating a large number of seed particles in a very short time, which are then multiplied by the RREA process by a few orders of magnitude. It could also involve some level of relativistic feedback. Furthermore, ALOFT observations suggest that weak TGFs may be due to an abrupt increase in the seed population rather than an increase in the electric field, given the fast rise time (too fast for relativistic feedback) and the fact that the TGF precedes the radio signal.
EAS originate from highly energetic cosmic-ray protons and nuclei showering in the atmosphere. Because Geant4 cannot simulate initial proton energies above 100 TeV, and such energies may be required, we will also use the CORSIKA code (high-energy part) with the FLUKA model (low-energy part), both of which are well-established reference models. A key here to evaluate this hypothesis, is the trade-off between initial cosmic proton fluxes (e.g., per hour per square kilometer) and their energies, as higher energies generate more seed electrons but are less frequent.
In this presentation, we will show a comprehensive evaluation of the possibility of generating weak TGFs via EAS energetic electron seeding in a realistic large-scale thunderstorm electric field close to the RREA threshold.
References:
I. Bjørge-Engeland et al. Evidence of a New Population of Weak Terrestrial Gamma-Ray Flashes Observed From Aircraft Altitude. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL110395
A. Fuglestad et al. The source brightness distribution of Terrestrial Gamma-ray Flashes from the ALOFT flight campaign.
J. R. Dwyer. Source mechanisms of terrestrial gamma-ray flashes. https://doi.org/10.1029/2007JD009248
Carlson, B. E., N. Lehtinen et al. (2008). Runaway relativistic electron avalanche seeding in the Earth’s atmosphere. https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008JA013210
How to cite: Sarria, D., Marisaldi, M., Østgaard, N., Mezentsev, A., Lehtinen, N., Færder, Ø., Bjørge-Engeland, I., and Fuglestad, A.: Investigating Cosmic-Ray Extensive Air Showers as a Source of Weak TGFs Using GEANT4 and CORSIKA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17409, https://doi.org/10.5194/egusphere-egu26-17409, 2026.
