NH1.5

We present an analysis of the evolution of PG during the course of rain, hail and snow events at the Xanthi site, N. Greece. In particular, using data from eight rain events in 2021, four hail events in the period 2018-2021 and four snow events during the same period, we examine how the PG frequency distribution changes during the progression of these events and discuss potential implications for the charge of the hydrometeors and the clouds that produce them. We also present some first results from recently started measurements of PG and lightning at the high altitude (2340 m ASL) site of Helmos Observatory, Peloponnese, Greece.

How to cite: Kourtidis, K., Misios, S., Karagioras, A., and Kosmadakis, I.: Measurements of PG during rain, hail, snow and lightning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1653, https://doi.org/10.5194/egusphere-egu22-1653, 2022.

Nowadays, there is a great need for the preservation of historical data in earth sciences as time series covering a long time period are of extreme importance in studying long-term variations of the Earth’s environment. This is the case in the field of atmospheric electricity research, too. In this work, we focus on one of the most frequently recorded parameters of the discipline, the atmospheric electric potential gradient (PG).

The PG is the reverse of the vertical atmospheric electric field, a quasi-DC quantity measured in Vm-1 units usually near the ground most often at 1–3 m heights [1]. The PG has been measured quasi-continuously at the Széchenyi István Geophysical Observatory near Nagycenk, Hungary (NCK, 47°38’ N, 16°43’ E) since 1962 [2]. Between 1962 and 2011, the PG was recorded on photo papers which were evaluated manually and the hourly averaged PG values were archived. Nevertheless, the original photopapers, too, were kept.

In this contribution, we present a recently developed image processing algorithm to digitize the analogue PG records on the old photo papers semi-automatically. By means of this algorithm, PG averages can be obtained with a temporal resolution as high as 30 s. In order to validate the digitized data, they have been compared to the archived hourly PG averages between 1999 and 2009. The long-term, seasonal, and diurnal variations of the PG at NCK between 1999 and 2009 based on the digitized and the archived data are also presented.

[1] Rycroft, M. J., Israelsson, S., and Price, C.: The global atmospheric electric circuit, solar activity and climate change, J. Atmos. Sol.-Terr. Phy., 62, 1563–1576, 2000.

[2] Bór, J., Sátori, G., Barta, V., Szabóné-André, K., Szendrői, J., Wesztergom, V., Bozóki, T., Buzás, A., and Koronczay, D.: Measurements of atmospheric electricity in the Széchenyi István Geophysical Observatory, Hungary, Hist. Geo Space. Sci., 11, 53–70, https://doi.org/10.5194/hgss-11-53-2020, 2020.

How to cite: Magos, L., Bozóki, T., Bozsó, I., Bór, J., Horváth, A., Kuslits, L., Timkó, M., and Buzás, A.: Digitizing archive atmospheric electric potential gradient data for scientific research, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5228, https://doi.org/10.5194/egusphere-egu22-5228, 2022.

Charge influences the properties of liquid droplets, such as their evaporation rates, hydrodynamic stability and sticking probabilities in droplet-droplet collisions. Introducing additional charge into an assembly of droplets therefore provides a possible method of influencing the droplet properties, and, in the case of a fog or cloud, a route to weather modification. The effect of charging on natural droplets has been investigated by releasing additional unipolar and bipolar ions into a natural surface fog, from both within the fog at the surface and above the fog, using an Uncrewed Aerial Vehicle (UAV). Droplet properties were monitored before and after the ion release using optical methods, together with the atmospheric electric field using a field mill. The atmospheric electric field measurements robustly demonstrate the present of the additional ions. Further, changes in the fog properties apparent when the additional ions are introduced are discussed.

How to cite: Harrison, G., Marlton, G., Ambaum, M., and Nicoll, K.: Releasing corona ions into natural fog, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8665, https://doi.org/10.5194/egusphere-egu22-8665, 2022.

SOFT-IO-LI is a new tool merging space and ground based lightning observations and aircraft NOx measurements to provide a database of new parameters characterizing lightning-NOx air masses observed at the global scale, to the scientific community.

The tool takes lightning-NOx air masses measured by IAGOS (In-service Aircraft for a Global Observing System) a European Research Infrastructure for global observations of atmospheric composition using commercial aircraft. FLEXPART the Lagrangian transport and dispersion model is used, together with ERA5 reanalysis weather data from ECMWF, to perform a backward trajectory of these air masses, resulting in hourly mass residence times for lightning-NOx particles for the days prior to the flight measurements.

We will present, for IAGOS transatlantic flights, the comparison of these mass residence times with ground based NLDN (National Lightning Detection Network) and space based GLM (Global Lightning Mapper) lightning observations, as well as with ABI (Advanced Baseline Imager) cloud data. We will show that SOFT-IO-LI is capable of relating lightning events and chemical species observed in situ, in order to determine characteristics of the different lightning-related air masses.

How to cite: Mackay, C., Sauvage, B., Wolff, P., Defer, E., Mahnke, C., Petzold, A., Bundke, U., and Kennert, M.: SOFT-IO-LI: a new tool merging space and ground based lightning observations and aircraft NOx measurements., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7794, https://doi.org/10.5194/egusphere-egu22-7794, 2022.

Lightning in winter (December, January, February, DJF) is rare compared to lightning in summer (June, July, August, JJA) in central Europe. The conventional explanation attributes the scarcity of winter lightning to seasonally low values of variables that create favorable conditions in summer. Here we systematically examine whether different meteorological processes are at play in winter. We use cluster analysis and principal component analysis and find physically meaningful groups in ERA5 atmospheric reanalysis data and lightning data for northern Germany. Two sets of conditions emerged: Wind-field dominated and mass-field (temperature) dominated lightning conditions. Wind-field type lightning is characterized by increased wind speeds, high cloud shear, large dissipation of kinetic energy in the boundary layer, and moderate temperatures. Clouds are close to the ground and a relatively large fraction of the clouds is warmer than −10 degree Celsius. Mass-field type lightning is characterized by increased convective available potential energy (CAPE), the presence of convective inhibition (CIN), high temperatures, and accompanying large amounts of water vapor. Large amounts of cloud-physics variables related to charge separation such as ice particles and solid hydrometeors further differentiate both mass-field and wind-field lightning. Winter lightning is wind-field driven whereas in summer lightning is mostly mass-field driven with a small fraction of cases being wind-field driven. Consequently, typical weather situations for wind-field lightning in the study area in northern Germany are strong westerlies with embedded cyclones. For mass-field lightning, the area is typically on the anticyclonic side of a southwesterly jet.

Keywords: ERA5, cold-season thunderstorm, k-means clustering, winter lightning.

How to cite: Morgenstern, D., Stucke, I., Simon, T., Mayr, G. J., and Zeileis, A.: Differentiating lightning in winter and summer with characteristics of wind field and mass field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-824, https://doi.org/10.5194/egusphere-egu22-824, 2022.

Lightning activity is predicted to increase with global warming, though estimates of lightning sensitivity to a change of temperature vary widely.  Since lightning is a small scale process, it must be represented by parameterizations in climate models. This paper uses large-scale meteorological parameters tied to thunderstorm generation to improve existing empirical models that simulate regional thunderstorm behavior. This study focuses on Tropical America, and uses the ERA5 higher resolution reanalysis data (ERA5) to develop our empirical model.  Thunderstorm data were taken from the World Wide Lightning Location Network (WWLLN) and processed using the clustering algorithm developed by Mezuman et al. (2014). The two meteorological parameters that correlated best with thunderstorm clusters in Tropical America were specific humidity (SH) and convective available potential energy (CAPE).  The resulting empirical model was run from 1979-2019 using ERA5 reanalysis data as input. This approach enables the observation of long-term trends in the behavior of thunderstorms in the regions, in the absence of a complete historical lightning record. To our surprise, Tropical American thunderstorms exhibited a negative trend over this period, with a ~8% decrease in thunderstorm clusters since the 1980s even with a rise of 1K in temperature over the same period. The regions of largest decreases in thunderstorm activity align well with estimates of deforestation.  We estimate that for every 1 Tg C lost due to deforestation, there is a 10% decrease in thunderstorm number.

How to cite: Price, C., Bekenstein, R., and Mareev, E.: Is Amazon deforestation decreasing the number of thunderstorms over Tropical America?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4393, https://doi.org/10.5194/egusphere-egu22-4393, 2022.

Lightning location information has a broad range of uses from Nowcasting through to aviation safety. Hence, the Met Office, based in the United Kingdom, has operated Lightning location systems since 1935. Here the Met Office’s next generation VLF lightning location system: Lightning Electromagnetic Emission Location using Arrival time differencing (LEELA) is described. It is set to replace ATDnet, the Met Office’s current operational system in 2022. LEELA features newly designed hardware and processing architecture, with a new novel technique to extract the sferics from the raw VLF data, and new fixing algorithms that improve location accuracy and detection efficiency over that of ATDnet. The night time issues from modal interference that ATDnet suffered from have been mitigated against and the night time performance of LEELA is improved. It will be shown that LEELA can provide lightning information over Europe, Africa, middle east and central America. In addition to this, the new processing architecture means that a near constant stream of VLF data is recorded and archived allowing investigations into sudden Ionospheric disturbances by observing changes in received power from VLF transmitters.

How to cite: Marlton, G., Potts, M., Twelves, S., Prust, S., Stone, E., and O'Sullivan, D.: LEELA: The Met Offices next generation lightning location system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2541, https://doi.org/10.5194/egusphere-egu22-2541, 2022.

The north-western Mediterranean basin often experiences thunderstorms with heavy precipitation and intense lightning activity causing damages to this densely populated area. This study is conducted within the framework of the EXAEDRE (EXploiting new Atmospheric Electricity Data for Research and the Environment) project that aims to better monitor the thunderstorms in this area through a better understanding of the physical processes that drive the dynamics, the microphysics and the electrical activity of the convective systems. These thunderstorms can exhibit distinct vertical charge structures (normal and anomalous) that produce lightning flashes with different properties. The goal of this study is to compare these characteristics (CG production, flash polarity...) according to both charge structures as measured in Corsica.

The study evaluates the properties of both types of Corsican storms at the electrical cell scale. Hence, observations of the LMA (Lightning Mapping Array) SAETTA network, deployed in Corsica, are used to document in 3D the total lightning activity. Complementary 2D lightning observations recorded by the French LLS (Lightning Locating System) METEORAGE are also used. We also add Météo France weather radar data to document the cumulative rainfall associated to each electrical cell. A clustering algorithm is applied on the lightning data to identify and track the cells. Then we extract lightning and radar data for each cell to document the evolution of several lightning-related parameters during their lifetime. We also apply a recently published method to automatically infer the vertical structure of the electrical charge regions within each cell. These algorithms allow us to create a database of hundreds of electrical cells in Corsica for the period of study (June – October 2018).

We first introduce the different observations and methodologies applied here. Then we present the geographical and temporal distribution of the normal and anomalous cells over the study period. Finally we compare the electrical properties associated to these different vertical charge structure configuration. Overall, anomalous cells represented around 15% of the cells population in Corsica over the study period. Anomalous storms produced less lightning jumps per cell but produced more CGs relative to the total number of flashes per cell. We also show that anomalous cells tend to form shorter flashes. The relationship between number of CGs and cumulative rainfall in Corsica for both charge structure is linear and in accordance with previous results.

How to cite: Houel, R., Defer, E., Lambert, D., Prieur, S., Pédeboy, S., Gaussiat, N., and Radojevic, M.: Normal versus anomalous thunderstorms, a comparison of electrical cells properties observed with the SAETTA LMA over the Corsican island, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4025, https://doi.org/10.5194/egusphere-egu22-4025, 2022.

Despite its scarcity, upward lightning initiated from tall structures causes more damage than common downward lightning. One particular subtype with a continuous current only is not detectable by conventional lightning location systems (LLS) causing a significantly reduced detection efficiency. Upward lightning has become a major concern due to the recent push in the field of renewable wind energy generation . The growing number of tall wind turbines increased lightning related damages. Upward lightning may be initiated by the tall structure triggering the flash itself (self-triggered) or by a flash striking close by (other-triggered).

The major objective of this study is to find the driving atmospheric conditions influencing whether an upward flash is self-triggered or other-triggered and whether it is of the undetectable subtype. We explore upward flashes directly measured at the Gaisberg Tower in Salzburg (Austria) between 2000 and 2015. These upward flashes are combined with atmospheric reanalysis data stratified into five main meteorological groups: cloud physics, mass field, moisture field, surface exchange and wind field. We use classification methods based on tree-structured ensembles in form of conditional random forests. From these random forests we assess the meteorological influence and find the most important atmospheric drivers for one event or the other, respectively.

Whether upward lightning is self-triggered or other-triggered can be reliably explained by meteorology. The closer the -10  °C isotherm is to the tall structure, the higher is the probability of self-triggered flashes. On the other hand, lower proportions of solid hydrometeors, supercooled liquid water and lower amounts of large scale precipitation increase the probability of an initial continuous current only flash type. However, the occurrence of nearby lightning discharges is about ten times more important for the type of upward flash. No nearby discharges (or them being further than 4 km away) considerably increases the probability of the initial continuous current only flash type.

How to cite: Stucke, I., Morgenstern, D., Simon, T., Mayr, G. J., Diendorfer, G., Schulz, W., Pichler, H., and Zeileis, A.: Upward lightning at tall structures: Atmospheric drivers for trigger mechanisms and flash type, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-958, https://doi.org/10.5194/egusphere-egu22-958, 2022.

We have developed a new electrodynamic return stroke (RS) model, which is based on solving the full set of Maxwell’s equation together with the electrostatic Poission’s equation for a realistic thundercloud charge structure. The evolution of the line conductivity of the RS channel is characterized by a nonlinear resistance model. The RS channel consists of a vertical channel connecting the ground with the thundercloud and a horizontal in-cloud channel. The RS processes are initiated by adding a zero potential element into the bottom end of the vertical channel. The channel-base current does not have a predefined form, but results from our model. We show the comparison of the modeled magnetic field waveforms with the observations at distances of tens of kilometers from their source lightning discharge. We also verify the simulated electric and magnetic field RS waveforms at shorter distances and compare them with their typical shapes found in the literature. The line charge density and the electric potential prior to and after the RS initiation are also investigated from the point of view of the bidirectional leader concept.

How to cite: Kaspar, P., Kolmasova, I., and Santolik, O.: The electrodynamic model of the return stroke processes involving a bipolar leader scheme, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4157, https://doi.org/10.5194/egusphere-egu22-4157, 2022.

In continuation of the study reported last year, we report additional results from imaging lightning initiation via interferometric beamforming of data collected by the Dutch LOw Frequency ARray (LOFAR).  Significant improvements have been incorporated into the analysis, including: more accurate antenna characterization, improvements to location accuracy, and the inclusion of a polarization model [Scholten, O., et al., PRD DD12993].  This project complements and enhances the previous work of the LOFAR lightning group of Groningen [Hare, B.M., et al., Nature 568, 360363 (2019)] and [Scholten, O., et al., ESSOAr 10503153] and elucidates regions in which there are a high number of sources within a short duration of time.  Interferometric beamforming techniques enhance both spatial and temporal resolution of lightning sources and as a result, locates and images the first non-impulsive sources in lightning flashes.  These sources are believed to be caused by a streamer-cascade-like initiation event which leads to the formation of the first leader.  Previously observed initiation events start from essentially background and within tens of microseconds ramp up a few orders of magnitude before the first impulsive sources connected with lightning leaders are observed.  The new techniques build upon those previously reported [Sterpka, C., et al., Geophysical Research Letters 48 (2021)] and [Sterpka, C., et al., EGU General Assembly EGU21-13711 (2021)], uncovering new detail in the lightning initiation region and characterization of additional flashes.  This new data includes a slow-propagating initiation discharge, starting 60 ms before the formation of the corresponding lightning leader.  The discharge is within 50 m of the initiation of the lightning leader and propagation speed of this discharge is about 700 ± 30  m/s, comparable to the ion drift speed.  This discharge continues for 30 ms before ceasing, and is likely a failed initiation attempt.

How to cite: Sterpka, C., Dwyer, J., Liu, N., Demers, N., Hare, B., and Scholten, O.: Uncharacteristically Slow Discharge Process Observed Preceding Lightning Initiation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6066, https://doi.org/10.5194/egusphere-egu22-6066, 2022.

Lightning is inherently a spatio-temporal process with individual lightning strikes represented by their time of occurrence and spatial coordinates. In this paper, we characterise and model lightning strikes in time and space from single thunderstorms, considering each set of lightning strikes to be a set of point events. This allows for real-world datasets to characterise lightning strikes and their physical properties. We select two case studies of severe thunderstorm systems over the UK, based on their synoptic analysis information as available in the published literature. This information allows us to separate the lightning strike dataset into subsets representing individual thunderstorms producing these strikes. We first identify three supercell thunderstorms with 7955, 11988 and 5655 lightning strikes from the larger storm system that crossed the English Midlands on 28 June 2012. A second set of three structurally different severe thunderstorms with 4218, 455 and 1926 lightning strikes was selected from a severe storm system across northern England on 1 to 2 July 2015. The six lightning strike datasets are representative of individual thunderstorms and each examined with regards to three physical properties: storm movement speed, lightning inter-event time distribution and lightning spatial spread distribution about the storm track. We use a least-squares plane fit in the spatio-temporal domain to estimate a range of representative movement speed values, finding 46-52 km/h for the first storm system and 67-105 km/h for the second. For inter-event time distribution, we find that values range from 0.01 to 100 s with all thunderstorms showing two peaks in density values around 0.1 s and between 1 and 10 s. To identify temporal structure in the inter-event time series, we perform autocorrelation analysis in natural time, which returns statistically significant autocorrelation values for all thunderstorms with some storms exhibiting short-range and others long-range autocorrelation. For estimating the storm track about which the orthogonal distances are calculated between the storm track and the lightning strikes, we consider orthogonal distance regression in the two-dimensional space domain. The analysis is done similarly to inter-event times for these orthogonal distances. We find a typical range of spatial spread values to be up to 50 km in magnitude, with one thunderstorm having exceptionally high values of up to 150 km. Autocorrelation analysis of these orthogonal distance values in natural time also return significant results that vary between individual thunderstorms. Finally, we present a synthetic lightning strike model where we can freely select the number of individual storms, their starting points, direction and movement speeds. For each storm, the point events after the starting point are produced about the storm track with inter-event times and orthogonal distance values taken from synthetic time series based on the analysis done during the characterisation. The characterisation in this paper of lightning strikes in time and space is representative of real-world severe thunderstorms and can inform statistical models to simulate lightning strike events.

How to cite: Zandovskis, U., Malamud, B. D., and Pigoli, D.: Characterisation and modelling of lightning strikes in time and space, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10295, https://doi.org/10.5194/egusphere-egu22-10295, 2022.

Negative lightning leaders, which are associated with the production of terrestrial gamma-ray flashes, prolonged X- and gamma-ray glows and neutron beams, move in a step-wise manner when the original leader channel connects to the hot, highly conductive space leader forming ahead of the leader tip. However, details about the formation and heating of the space leader, and thus of the leader stepping process, are still unknown. Here, we present a novel mechanism on the origin of space leaders: After streamer coronae have formed ahead of the leader tip, plasma chemistry and heating turn a selection of the corona streamers into a highly-conductive region. Further heating subsequently allows for the inception of secondary streamer coronae at the vertices of the conductive region, which continue to heat the already heated plasma filament, finally translating into the hot and conductive space leader. We simulate the evolution of the electric field and the associated plasma chemistry in single streamer channels and present the temporal evolution of the electron density and the electric field as well as of the temperature increase and the conductivity. We find that one streamer alone cannot be heated sufficiently towards a hot space leader, but that the inception and evolution of branching streamer coronae from this initial streamer are necessary for further heating.

How to cite: Köhn, C., Babich, L., Kutsyk, I., Bochkov, E., and Neubert, T.: The formation of space leaders in streamer coronae of negative leaders, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7799, https://doi.org/10.5194/egusphere-egu22-7799, 2022.

Streamer discharges are often seen as the building blocks of sparks by playing a major role in their initiation and propagation. The stagnation of streamers is of great interest from the scientific point of view and for industrial applications since it helps defining a maximal length over which a streamer can propagate. Therefore, understanding the stagnation helps the design of high voltage equipment like circuit breakers and gas insulated systems.

In this presentation, we study the stagnation of positive streamers by means of numerical modelling. For negative streamers, the modelling of the stagnation mechanism is relatively straight forward, since the streamer head enlarges, and the tip electric field vanishes smoothly. For positive streamers, the modelling is more challenging since a classical drift-diffusion model with the local field approximation usually leads to an unstable increase of the streamer tip electric field.

In our recent results published in [1] and [2], we show that the instability originates mostly from the local field approximation for the calculation of the ionization source term, and we show that the non-local treatment of the ionization leads to a successful simulation of stagnation. We use 2 different models for the treatment of ionization; the first is a classical model in which the ionization source term in the streamer tip is slightly smoothed [1] and the second, which is based on an extended model [3,4].

The successful simulation allows to observe the physical mechanisms behind the stagnation of streamer discharges by showing the role of positive ions and makes it possible to determine the maximal length a streamer can reach.

[1] Niknezhad M, Chanrion O, Köhn C, Holbøll J & Neubert T 2021, 'A three-dimensional model of streamer discharges in unsteady airflow: Paper', Plasma Sources Science and Technology, vol. 30, no. 4, 045012. 

[2] Niknezhad M, Chanrion O, Holbøll J & Neubert T 2021, 'Underlying mechanism of the stagnation of positive streamers', Plasma Sources Science and Technology, vol. 30, no. 11, 115014.

[3] Aleksandrov N L and Kochetov I V 1996, ’Electron rate coefficients in gases under non-uniform field and electron density conditions’, Journal of Physics D: Applied Physics, vol. 29, no. 6, 1476—1483.

[4] Li C, Ebert U, Hundsdorfer W 2010, , Spatially hybrid computations for streamer discharges with generic features of pulled fronts: I. Planar fronts', Journal of Computational Physics, vol. 229, 200-220.

How to cite: Chanrion, O., Niknezhad, M., Holbøll, J., and Neubert, T.: Some results on streamer stagnation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10606, https://doi.org/10.5194/egusphere-egu22-10606, 2022.

Sulfur hexafluoride (SF₆) and carbon tetrafluoride (CF₄) are inert gases in the atmosphere that can absorb infrared radiation and affect the climate. They have lifetimes up to 1278 years for SF₆ and 50000 years for CF₄. The International Panel on Climate Change lists the two as part of the most influential long-lived, well-mixed greenhouse gases, with SF₆ having the highest identified global warming potential. Both gases have anthropogenic major sources. SF₆ is used as an insulating gas in the electrical power industry, and CF₄ is a by-product of aluminum manufacturing. In this study, we question whether atmospheric electricity significantly influences the atmospheric concentrations of these molecules. We aim to investigate SF₆ and CF₄ decomposition within streamers at different altitudes in the atmosphere, and then estimate the global occurrence rate of such streamers and their impact. To accomplish this, we simulate positive streamers in synthetic air that contains a small concentration of the two gases. From our simulations, we identify relations between streamer properties and the amounts of SF₆ and CF₄ destroyed, which can be used to estimate the rates of chemical processes in observed streamer events.

How to cite: Francisco, H., Ebert, U., Fullekrug, M., and Plane, J.: Decomposition of long-lived greenhouse gases by atmospheric streamers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8701, https://doi.org/10.5194/egusphere-egu22-8701, 2022.

Streamers are an important stage of lightning, taking place before the formation of a leader discharge. The goal of the novel Streamer Parameter Model (SPM) is to explain the mechanism that determines the parameters of a streamer, such as its radius and propagation velocity. We demonstrate that SPM predictions agree well with the published hydrodynamic simulation (HDS) results [1]. The discrepancies between SPM and HDS were of the same order of magnitude as the discrepancies between different HDS codes. The comparison was performed for two different streamer propagation mechanisms: photoionization and background ionization. The largest discrepancies were for the case of low background ionization, which was also challenging for HDS. Electron diffusion did not change the streamer parameters significantly. We propose that SPM, despite the crudeness of the model, provides a computationally simple way to reliably assess streamer properties.

How to cite: Lehtinen, N. and Marskar, R.: Verification of the Streamer Parameter Model by comparing to Hydrodynamic Simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6211, https://doi.org/10.5194/egusphere-egu22-6211, 2022.

X-rays have been observed in downward cloud-to-ground lightning and rocket-triggered lightning for the case of negative leaders both during the leader stepping and the dart leader phase [1-3]. X-rays have also been observed during the stepping of dart leaders in upward negative lightning flashes [4,5].      

In this study, we present results from three positive upward flashes. The observations consist of the simultaneous records of X-rays, electric current and electric field at 23 m. Observations from a 2D interferometer system are available for two of the flashes while the third flash was captured by a high-speed camera operating at 24 000 frames per second.

We report X-rays recorded during the initial phase of upward negative leader propagation. To the best of our knowledge, this is the first time that such observations are reported in the literature. The observed X-rays are associated with the stepping of upward negative leaders that can be observed both in the electric field and current waveforms. X-rays associated with the very first step of the upward negative leader were observed in one of the three flashes.

These observations are important to understand the initiation of upward lightning and the mechanisms involved in the initial breakdown.          

[1] Moore, C. B., Eack, K. B., Aulich, G. D., & Rison, W. (2001). Energetic radiation associated with lightning stepped-leaders. Geophysical Research Letters, 28(11), 2141–2144. https://doi.org/10.1029/2001gl013140

[2] Dwyer, J. R. (2003). Energetic Radiation Produced During Rocket-Triggered Lightning. Science, 299(5607), 694–697. https://doi.org/10.1126/science.1078940

[3] Bowers, G. S., Smith, D. M., Martinez‐McKinney, G. F., Kamogawa, M., Cummer, S. A., Dwyer, J. R., Wang, D., Stock, M., & Kawasaki, Z. (2017). Gamma Ray Signatures of Neutrons From a Terrestrial Gamma Ray Flash. Geophysical Research Letters, 44(19). https://doi.org/10.1002/2017gl075071

[4] Hettiarachchi, P., Cooray, V., Diendorfer, G., Pichler, H., Dwyer, J., & Rahman, M. (2018). X-ray Observations at Gaisberg Tower. Atmosphere, 9(1), 20. https://doi.org/10.3390/atmos9010020

[5] Sunjerga, A., Hettiarachchi, P., Smith, D., Rubinstein, M., Cooray, V., Azadifar, M., Mostajabi, A., & Rachidi, F. (2021). X-rays observations at the Santis Tower: Preliminary results. Copernicus GmbH. https://doi.org/10.5194/egusphere-egu21-9586

How to cite: Sunjerga, A., Hettiarachchi, P., Stanley, M., Smith, D., Chaffin, J., John, O., Cooray, V., Rubinstein, M., and Rachidi, F.: X-rays associated with the stepping of upward negative leaders at the Säntis Tower: Preliminary results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11214, https://doi.org/10.5194/egusphere-egu22-11214, 2022.

Gamma-Flash is an Italian program devoted to the investigation of radiation and particles produced during lightning and thunderstorms. The project is funded by the Italian Space Agency (ASI) and led by the National Institute for Astrophysics (INAF), with the collaboration of numerous institutions and universities. The aim of the project is the study and development of an innovative gamma-ray and neutron detector, and correlative instruments, to be placed onground, at the Climatic Observatory "O. Vittori" on Mt. Cimone (2165 m a.s.l., Northern-Central Italy). In a second phase, the program foresees the development of another payload, to be placed on aircraft for observations of thunderstorms in the air. Gamma-Flash is designed to detect both short-duration transients, such as terrestrial gamma-ray flashes (TGFs), as well as longer-lasting gamma-ray emissions, such as gamma-ray glows, and associated high-energy particle emissions. Main targets of the program are the study of high-energy emissions in thunderstorms, which can have substantial impact in many fields, such as local/global climate change, environmental studies, and atmospheric plasma physics. In addition, the experiment is aimed at the estimate of the susceptibility of electronic systems and devices to TGF-induced ionizing radiation and particles. The investigation of thunderstorm-related high-energy emissions will be supported by a continuous monitoring of the correlated atmospheric scenario, by means of meteorological data analysis on a local scale. The Gamma-Flash group shares cutting-edge expertise in the field of atmospheric physics, high-energy particle and radiation instruments, radiation damage, data analysis, and simulations, taking advantage of more than ten years experience of the ASI AGILE satellite in the field of TGF studies. Gamma-Flash is currently in its design and development phase. The ground-based detector is on its way to the final implementation it will be operative starting from spring 2022. We present an overall description of the Gamma-Flash program, of its detectors, payload, and system design, and of its main scientific objectives.

How to cite: Ursi, A. and the Gamma-Flash Team: Gamma-Flash: an Experiment to Detect Radiation and Particles in Thunderstorms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12378, https://doi.org/10.5194/egusphere-egu22-12378, 2022.

The Pierre Auger Observatory, designed to study ultra-high energy cosmic rays, has accidentally observed, with its 3000 km² surface array of water-Cherenkov detectors, several events that are very likely downward TGFs. Their morphology, as well as the signals observed in the detectors, are totally different from what observed when an extensive air shower strikes the array. The TGF-like events are characterized by large footprints (~200 km²) and long signals (~ 10 µs), if compared to cosmic-ray showers. They happen in coincidence with lightning as demonstrated by the correlation with WWLLN data and with strong variations observed in the electric fields measured by the E-mills available at the Observatory. Other events within 1 ms of these peculiar events were observed in the same zone of the array. This time interval is about the time taken by the steeped leader to reach its full length. Finally, from a first reconstruction, the source altitude of this events is estimated to be very close to ground, at about 1-2 km. From lidar measurements, we know that there were low clouds at altitudes compatible with the estimated source location at the time of many events. The source altitudes can be used as input parameter for the REAM simulation to start a campaign to compare our experimental results with TGF models. The rate of TGF-like events per year is very low, less than 2 events per year. To increase the statistics, a modification to the read-out logic to give priority to events which contain long signals was implemented ans is under test.

How to cite: Colalillo, R. and Dwyer, J. and the Pierre Auger Collaboration: The hidden power of lightning: studying the most explosive events in thunderstorms with the world’s largest cosmic-ray observatory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12119, https://doi.org/10.5194/egusphere-egu22-12119, 2022.

Atmosphere Space Interaction Monitor (ASIM) has now observed more than 1000 Terrestrila Gamma-ray falshes (TGFs) since the launch in 2018. ASIM has two payloads, the Modular X- and Gamma-ray Sensor (MXGS) and the Modular Multi-Spectral Imaging Assembly (MMIA). MXGS consists of two detector layers, one pixelated detector in the low energy range (50 keV to 400 keV) and another in the high energy range (300 keV to >30 MeV), with temporal resolution of 1µs and 28 ns, respectively.  MMIA has three photometers (337 nm, 180-230 nm, 777 nm) and two cameras (337 nm and 777 nm). During nighttime we observe both the TGFs and the lightning that produced them. Multiple and double TGFs  separated by 1-2 ms have frequently been observed by ASIM. In this paper we present three events of double TGFs. All of them are associated with  optical pulses from a hot leader (777 nm), and the first and second pulses come from the same location, indicating that the double TGFs are produced by the same leader as it propagates upward. 

How to cite: Ostgaard, N., Mezentsev, A., Marisaldi, M., Sarria, D., Ullaland, K., Yang, S., Genov, G., Neubert, T., Chanrion, O., Christiansen, F., Cummer, S., Lu, G., Reglero, V., and Luque, A.: Double TGFs and optical pulses observed by ASIM , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3382, https://doi.org/10.5194/egusphere-egu22-3382, 2022.

TGFs are short-duration bursts of high-energy photons shot from Earth’s atmosphere to space. They are produced during the initial upward propagation of +IC lightning leaders and are often associated with LF radio sferics. The Atmosphere-Space Interactions Monitor (ASIM) instrument provides X- and gamma-ray measurements synchronous with optical recordings in 180-240 nm, 337 nm and 777.4 nm wavelengths, allowing simultaneous detection of TGFs and the lightning processes associated with them.

ASIM observations show that TGFs are accompanied by a prominent optical pulse that marks the beginning of a lightning flash. TGFs tend to precede the pulse slightly, but the short duration of TGFs, together with the delay of the optical pulses from photon scattering in cloud particles, does not allow to resolve the correct sequence of events with confidence.

The same problem is present in measurements of radio waves, where the waves emitted by the TGF currents usually are mixed with those of the lightning currents because of the temporal proximity of the processes.

Here we report a remarkable TGF, with a high fluence of 360 counts in the energy range 0.4 - 20 MeV and a relatively long duration of 580 µs. The associated optical pulse is clearly following the TGF, which leads us to conclude that the current surge inside the leader channel is not generating the TGF, as has been proposed by models, but instead that the TGF process conditions the current surge that follows.

How to cite: Mezentsev, A., Østgaard, N., Marisaldi, M., Neubert, T., Chanrion, O., and Reglero, V.: Discerning TGF and leader current pulse in ASIM observation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4240, https://doi.org/10.5194/egusphere-egu22-4240, 2022.

On January 10th 2022 the ASIM mission to the ISS was moved to the SDN mount point on the Columbus module for observations towards the earth rim and the cosmos. This enabled the ASIM/MXGS imager spectrometer to observe TGFs in a small ISS nadir FOV covering 35-65 degrees off-axis, and GRBs in the cosmos which covers most of its FOV. We present here initial results of imaging locations for off-axis TGFs with a low spectral hardness ratio and a much larger event count due to the reduction in the "flux cosine effect", and how this might facilitate estimates of mean TGF altitude. We also present the first MXGS location images of second long GRBs and their associated lightcurves and spectra.

How to cite: Connell, P., Reglero, V., Navarro, J., and Eyles, C.: Imaging TGFs and GRBs from the earth rim mounting of the ASIM/MXGS imager-spectrometer on the ISS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3037, https://doi.org/10.5194/egusphere-egu22-3037, 2022.

Terrestrial Gamma-ray Flashes (TGFs) are short emissions of high-energy photons associated with thunderstorms. Since their discovery, it has been clear that they are associated with lightning, and several case studies have shown that the TGFs are produced in the initial phase of the lightning flash. However, it has not been tested whether this is true in general. Here we present such study using the largest TGF sample available to date from the RHESSI, Fermi, AGILE, ASIM catalogs, combined with ground-based radio lightning detection data. Based on stacking analysis of the TGFs and associated lightning activity, together with the high temporal resolution of the optical data from the ASIM photometers, we show that, indeed, TGFs are produced at the beginning of lightning flashes. We also find that the detected sferic activity from the source locations in many cases is enhanced during ~150 - 750 ms following the TGFs, as also reported in Omar et al. (2014) and Smith et al. (2016). This enhanced activity is not present in a randomly-selected sample of flashes, suggesting it is a characteristic property of a significant fraction of flashes that start with a TGF.

The study is submitted to JGR Atmospheres.

Omar et al. (2014), Characterizing the TGF-lightning relationship using ENTLN, AGU Fall Meeting 2014, Abstract AE31A-3388.

Smith et al. (2016), doi:10.1002/2016JD025395.

How to cite: Lindanger, A., Skeie, C. A., Marisaldi, M., Bjørge-Engeland, I., Østgaard, N., Mezentsev, A., Sarria, D., Lehtinen, N., Reglero, V., Chanrion, O., and Neubert, T.: Production of Terrestrial Gamma-ray Flashes During the Early Stages of Lightning Flashes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4386, https://doi.org/10.5194/egusphere-egu22-4386, 2022.

ASIM TGF catalog presents more than one thousand TGF from June 2018 till the end of 2021. Using this dataset, the detection rate of TGF by ASIM was about one TGF per day. The TGF detection is a stochastic process (each TGF is not related with the next) assuming this, the time-difference distribution between one detection and the next should fit an exponential distribution. This time between TGF events distribution fits the exponential with a significant deviation. We see an excess in the number of TGF separated by less than 5 min. From the expected value of less than 1% of the events, we have an 8% of the events in this range. We call that TGF population with a time separation of fewer than 5 minutes “Brother TGF”. Large storm areas could explain this deviation, because of the storm size or also the propagation effects of the TGF inside the storm as an effective mechanism to increase the TGF production in this region. This work we present is a detailed study of the most relevant “Brothers” in the ASIM TGF imaging list. With this, we can locate where these Brothers TGF are located, and add some clues about this Brother TGF production mechanism.

How to cite: Navarro-González, J., Connell, P., Eyles, C., Reglero, V., López, J. A., Montanyà, J., Marisaldi, M., Mezentzev, A., Kochkin, P., Lindanger, A., Sarria, D., Østgaard, N., Chanrion, O., Christiansen, F., and Neubert, T.: Brother TGF, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8201, https://doi.org/10.5194/egusphere-egu22-8201, 2022.

Relativistic electrons in strong large-scale thunderstorm electric fields can obtain more energy from acceleration by the electric field than they on average lose on interactions with air molecules. Such accelerating electrons are called runaway electrons. Runaway electrons can produce additional runaway electrons by Moller scattering on air molecules. In this way, runaway electrons multiply and form a relativistic runaway electron avalanche (RREA).

In strong electric fields, RREA can multiply by relativistic feedback. Infinite relativistic feedback makes avalanches self-sustaining and could hypothetically trigger a terrestrial gamma-ray burst (TGF). This report presents the results of modeling the simplest reactor - the model of the appearance of a TGF, consisting of two cells looking at each other, their comparison with theoretical calculations and previous models.  It was found that the considered model predicts lower requirements for the electric field for the appearance of TGF than the others.

How to cite: Zemlianskaya, D. and Stadnichuk, E.: Simulation of the simplest reactor model of the dynamics of runaway electron avalanches in thunderclouds, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-563, https://doi.org/10.5194/egusphere-egu22-563, 2022.

Terrestrial Gamma-ray Flashes (TGFs) are short flashes of high-energy photons produced by thunderstorms. They are intense phenomena that may have high photon fluxes with energies up to 40 MeV when observed from detectors in orbit. All instruments in space have suffered instrumental saturation during bright events, including CGRO-BATSE, RHESSI, Fermi-GBM, AGILE-MCAL and ASIM-MXGS. The effects include dead-time and pulse pile-up, which lead to an underestimation of the TGF fluences and, in some cases, incorrect photon energies. 
    A key asset of ASIM is that it has two detectors on the same platform: the High Energy Detector (HED, 300 keV to ~40 MeV) and the Low Energy Detector (LED, 50 keV to 400 keV). LED is only weakly affected, which makes it possible to estimate corrections to the HED measurements for even the brightest TGFs. With the method we propose, we estimate the loss of photons by combining the LED and HED measurements with GEANT4 Monte-Carlo simulations of the detector responses. 
    We applied the method to three TGF events. The first, TGF-200728, has about 0.15 counts per microsecond  per unit, and is not expected to experience saturation and is used as a sanity check for the method. The other events, TGF-181102 (1.5 counts per microsecond per unit) and TGF-181025 (2.8 counts per microsecond per unit), indicate that the HED misses at least 50% of the photon counts for the brightest TGF events.

How to cite: Sarria, D., Østgaard, N., Marisaldi, M., Lindanger, A., Mezentsev, A., Lehtinen, N., Neubert, T., Christiansen, F., and Reglero, V.: Investigating the fluence of bright TGF events detected by the Atmosphere-Space Interactions Monitor, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7408, https://doi.org/10.5194/egusphere-egu22-7408, 2022.

Terrestrial gamma-ray flashes (TGFs) are short and highly energetic bursts of photons, produced in association with lightning in thunderstorms. Elves are rapidly expanding rings of optical emissions, with radii of several hundred kilometers, produced when electromagnetic pulses from lightning hit the base of the ionosphere. The Atmosphere-Space Interactions Monitor (ASIM) detects both TGFs and Elves, sometimes simultaneously. Here, we present a study of observations where TGFs are accompanied by Elves. The optical signatures from Elves are identified from measurements by the ASIM UV photometer. Using ground-based lightning location networks, we find associated sferic detections to these events, placing them mainly over oceans and in coastal regions. Using sferic detections by GLD360, we compare the peak currents of the lightning associated with the TGF-Elve pairs to peak currents associated with other TGFs detected by ASIM, as well as with lightning in general. We show that the TGFs accompanied by Elves are among the shorter TGFs detected by ASIM, and they are associated with very high peak currents of typically several hundred kA.

How to cite: Bjørge-Engeland, I., Østgaard, N., Mezentsev, A., Skeie, C. A., Sarria, D., Lapierre, J., Lindanger, A., Neubert, T., Marisaldi, M., Lehtinen, N., Chanrion, O., Ullaland, K., Yang, S., Genov, G., Christiansen, F., and Reglero, V.: Observations by ASIM of Terrestrial Gamma-ray Flashes accompanied by Elves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9085, https://doi.org/10.5194/egusphere-egu22-9085, 2022.

Narrow Bipolar Events (NBEs) are powerful radio emissions from thunderstorms, which sometimes occur isolated from lightning and at other times appear to initiate lightning. They are recently associated with Blue LUminous Events (BLUEs) on cloud tops and attributed to extensive streamer electrical discharges named fast breakdown, but their physics is not fully understood. Here, we analyse simultaneous observations of NBEs detected by radio receivers on the ground with their optical emissions observed by the Atmosphere-Space Interactions Monitor (ASIM) on the International Space Station (ISS). In this study, we focus on the multiple-pulse BLUEs that include one primary BLUE pulse and one or several subsequent BLUE pulses with a few millisecond intervals, as detected by a photometer at 337 nm. The observations indicate that the initial streamer discharge of an NBE is followed within a few milliseconds of horizontally oriented secondary streamer discharges at similar or higher altitudes but without triggering a leader process.

How to cite: Li, D., Luque, A., Lehtinen, N. G., Gordillo-Vázquez, F. J., Neubert, T., Lu, G., Chanrion, O., Zhang, H., Østgaard, N., and Reglero, V.: Multiple-pulse blue luminous events detected by ASIM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9138, https://doi.org/10.5194/egusphere-egu22-9138, 2022.

Blue electric streamer discharges in the upper reaches of thunderclouds are observed as flashes in the second positive band of molecular nitrogen at 337.0 nm (blue) with faint emissions from atomic oxygen at 777.4 nm (red), a dominant line of lightning leaders. Using 2.5 years of measurements by the Atmosphere-Space Interactions Monitor (ASIM) on the International Space Station (ISS), we find that their rise time distribution suggests two distinct categories. One includes those with fast rise times less than 30 mus that are relatively unaffected by cloud scattering and emanate from within ~2 km of the cloud tops, and the other those with longer rise times that come from deeper within the clouds. Satellite measurements show that the clouds with blue discharges have an average cloud top temperature ~200 K compared to ~210 K for those of normal lightning, suggesting that blue discharges occur in clouds that reach near the tropopause. The average convective available potential energy (CAPE) determined from ERA5 reanalysis data is ~1550 J/kg for the shallow events and ~1290 J/kg for the deeper events, compared to ~1010 J/kg for regular lightning, suggesting that the discharges favour strong convective environments. This is further indicated by the geographical distribution of blue discharges which show that they occur mainly near mountain ridges or coastlines known for their strongly convective environments.

How to cite: Husbjerg, L., Neubert, T., Chanrion, O., Dimitriadou, K., Stendel, M., Kaas, E., Østgaard, N., and Reglero, V.: Observations of Blue Corona Discharges in Thunderclouds, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7225, https://doi.org/10.5194/egusphere-egu22-7225, 2022.

The Rakia mission is a private space flight to the ISS, that was executed by the Axiom company in March 2022. The ILAN-ES (Imaging of Lightning And Nocturnal Emissions from Space) is heritage of the MEIDEX conducted on board the space shuttle Columbia in its final mission in January 2003 (Yair et al., 2004). We optimized the limited observation time (2 hours, 12x10 minutes) from the ISS such that only selected targets at prescribed times were imaged by the astronaut. We used an upgraded prediction procedure for potential TLE-producing thunderstorms, based on the verification scheme used during the THOR campaign (Chanrion et al., 2016), and by using the lightning location networks (WWLLN, ENTLN) data for selected active regions. In addition, we computed their magnetic conjugate points, so as to enlarge potential daily targets (geomagnetically conjugate sprites were never recorded from space; Marshal et al., 2005).

The camera used during ILAN-ES was a Nikon D6 set at 6400 ISO and recording 24 frames per second at 1920 x 1080 pixels. It was mounted with a 58mm/f1.2 lens, giving a 34.4^o x 19.75^o field of view corresponding to 1.07’/pixel. With these settings, the camera resolution was 130 m at nadir. The camera The astronauts operated the camera from the Copula window of the ISS while visually tracking lightning activity and directing the camera towards the bright flashes. When conjugate targets were allocated, the aim was to conduct nadir viewing.

To overcome the challenge of manual detection of lightning and transient luminous events in the video footage, we will harness several Machine Learning (ML) and Deep Learning (DL) techniques. A comprehensive ground-based campaign accompanied the ISS observations, most notably by the ground-based LEONA network in South America and by schools in Ghana, Rwanda and Zimbabwe.

This presentation will discuss mission operations and the results of the ISS and ground observations.

How to cite: Yair, Y., Price, C., Reuveni, Y., Yaniv, R., Sao Sabbas, E., and Rubanenko, L.: Results from targeted TLE and geomagnetically conjugate sprites observations from the International Space Station during the Rakia mission, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2485, https://doi.org/10.5194/egusphere-egu22-2485, 2022.

ELVES are being studied since 2013 with the twenty-four FD Telescopes of the Pierre Auger Observatory, the world’s largest facility for the study of ultra-high energy cosmic rays, in the province of Mendoza (Argentina) exploiting a dedicated trigger and extended readout. Since December 2020, this trigger has been extended to the three High Elevation Auger Telescopes (HEAT), which observe the night sky at elevation angles between 30 and 60 degrees, allowing to study ELVES from closer lightning. The high time resolution of the Auger telescopes allows to do detailed studies on multi-ELVES. The origin of multi-ELVES is not yet fully understood, and can be studied by analysing the time difference(s) and the amplitude ratio(s)  between flashes as a function of the radial distance of lightning emission from the causative lightning. At least two, if not three, distinct models are needed to explain the geometry of multi-ELVES events. This contribution will review the frequency of each class of multi-ELVES and correlate them to data from ENTLN, WWLLN, and GOES databases.

How to cite: Mussa, R. and the Pierre Auger Collaboration: Parametrization and Characterization of Multiple ELVES at the Pierre Auger Observatory , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7542, https://doi.org/10.5194/egusphere-egu22-7542, 2022.

Elves are rapidly expanding rings of optical emissions in the lower ionosphere. Narrow bipolar events (NBEs) are signatures in radio signals from intra-cloud discharges. They are thought to be fast streamer breakdown that may trigger the onset of lightning and blue jets. However, there is a lack of experimental evidence on whether the streamer discharges of NBEs carry sufficient currents to generate elves in the lower ionosphere. Here, we report the first simultaneous observation of NBEs and elves that confirm this hypothesis. The NBEs are observed simultaneously from the ground by an array of wave receivers located in China and from space by spectral measurements by the Atmosphere-Space Interactions Monitor (ASIM) on the International Space Station (ISS). We observe thirteen negative and six positive NBEs produced in four thunderclouds penetrating into the stratosphere. Five NBEs are accompanied by elve emissions observed in the near-ultraviolet of the Lyman–Birge–Hopfield (LBH) band.  They were at ~18 km altitude, and their peak currents, estimated by a ground-based lightning detection network, were larger than 135 kA. The observations show that the impulse currents of the streamers are of sufficient magnitude to power elves, thereby adding to the new pathways that thunderstorms affect the lower ionosphere. 

How to cite: Liu, F., Neubert, T., Chanrion, O., Zhu, B., Lu, G., Lyu, F., Dimitriadou, K., Lei, J., Østgaard, N., and Reglero, V.: Ionospheric elves powered by negative Narrow Bipolar Events in overshooting thunderclouds, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7949, https://doi.org/10.5194/egusphere-egu22-7949, 2022.