The ground-level potential gradient atmospheric electric field, the air conductivity, and concentration of cloud condensation nuclei have been recorded at Stanislaw Kalinowski Geophysical Observatory in Świder, Poland (52°07' N, 21°14' E), for several decades. A new digitisation project of Świder atmospheric electric data published in the observatory year books provides an opportunity to review the results of studies of the long-term variation of the electric parameters. New results of an analysis of both short-term and long-term variations in the positive conductivity and related component of the air-Earth current density are presented, and implications for the Global Electric Circuit studies using the Świder dataset are discussed. This work is supported by Poland National Science Centre grant no 2021/41/B/ST10/04448.

How to cite: Odzimek, A., Pawlak, I., and Kępski, D.: Analysis of long-term variations in fair-weather PG, the positive air conductivity and conduction current density at Geophysical Observatory in Świder, Poland, and implications for the Global Electric Circuit, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-977, https://doi.org/10.5194/egusphere-egu23-977, 2023.

    Existing literature indicates that volcanic lightning occurs during a devastating volcano eruption. However, it is still limited to understanding the volcanic electrification mechanism in nature because of the rarity of the explosive volcano eruption and visible spectrum obstacles from plumes full of dirty ashes. The eruption of the Hunga Tonga–Hunga Haʻapai (HT-HH) submarine volcanoes in the Lau Basin, South Pacific, had an extremely violate surtseyan type eruption on January 15^th and generated numerous volcanic lightning. This eruption event provides a great opportunity to explore the electrification and evolution of volcanic lightning. 

    In this work, more than 40,000 lightning events were detected by the World Wide Lightning Location Network (WWLLN) during the primary eruption on January 15^th. At the first stage of the eruption, the geographic distribution of lightning strikes expanded rapidly and isotropically while the eruption column reached a specific altitude. Then a lightning tranquility period occurred subsequently, implying explosive erupting was intermittent. Several explosive sub-eruptions were detected from 04:00Z to 07:00Z, and sub-eruptions' timestamps are highly consistent with seismic data analysis from IRIS. Lightning footprint provided evidence that the HT-HH eruption was a surtseyan eruption unsteady with several quiescent phases separating the explosive stages.

    HT-HH is one of the most powerful eruptions of the 21^st century and provides a favorable environment for volcanic lightning research. The result of this work can track the immediate eruption by using lightning activities. Moreover, volcanic lightning has a different charging mechanism than general tropospheric lightning. Therefore, many interesting issues can be discussed, such as the volcano eruption's contribution to global electrical circuits or whether volcanic lightning can generate other atmospheric electricity events like TLEs or TGFs.

How to cite: Lin, Y.-C. and Chen, A.: Characteristics of Volcanic Lightning Distribution Generated by Hunga Tonga–Hunga Haʻapai on January 15th, 2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4714, https://doi.org/10.5194/egusphere-egu23-4714, 2023.

The three years of IITM LLN lightning observation data are used to determine the seasonal and spatial (over different geographical locations) distribution of the ratio of intra-cloud lightning (IC) to cloud-to-ground lightning (CG) in thunderstorms over the Indian sub-continent. The ratio is high (8-10) in the north-western parts and low (0.3-3) in the north-eastern parts. There is not a prominent latitudinal variation of IC and CG ratio, but a climatological seasonal variability exists all over the regions. In the Pre-monsoon (March to May), the mean ratio is observed at 3.87 with a standard deviation of 0.74, and during Monsoon (June to September), that is 3.01 with a standard deviation of 0.52. Pre-monsoon thunderstorm exhibits more IC discharge comparatively monsoonal thunderstorms; hence IC:CG ratio is also high in pre-monsoon. We have observed that CG lightning is approximately 20% of total lightning in pre-monsoon whereas 25% of total lightning in monsoon all over the Indian region. High CAPE associated with a stronger vertical updraft enhances the cold cloud depth and expands the mixed phase region, which can broaden and uplift the size of the upper positive charge center inside a thunderstorm while the middle negative charge center remains at the same temperature level. Therefore it enhances the occurrence of IC discharge between the upper positive charge center and middle negative charge center, hence increasing the IC:CG ratio of a thunderstorm. The implication of these observed results has the importance of separating CG lightning flash from total and can be used in the numerical model to give a proper prediction of CG lightning in hazard mitigation.

How to cite: Ghosh, R., Pawar, S. D., Hazra, A., and Wilkinson, J.: Seasonal and regional distribution of lightning fraction over Indian Sub-continent, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-58, https://doi.org/10.5194/egusphere-egu23-58, 2023.

Over the last few decades, lightning has been one of the fatal extreme weather phenomena in the Indian subcontinent. Aerosols which act as cloud condensation nuclei (CCN) and ice nuclei (IN) can modify the cloud properties and alter the thermodynamic processes within the deep convective clouds in a way that eventually affects the lightning flash rates associated with thunderstorms. Long-term satellite observations suggest that a maximum number of lightning strikes (40-45 flashes/km²) occur during the pre-monsoon (March-May) and monsoon (June-September) seasons over the Indian subcontinent. We analyzed the lightning data available from satellite observations over two distinctly different climatological regions namely, northeast India and western India. In this study, we evaluate the performance of a numerical weather research and forecasting model (WRF) in reproducing the lighting characteristics over these two regions and further try to understand the sensitivity of simulated lightning flash rates to aerosol characteristics and aerosol-cloud interactions considered in the model.

Two severe lightning episodes which occurred on 5-6 May 2013 and 16 April 2019 over northeast India and western India respectively are chosen as case studies for our model sensitivity experiments. We used Morrison, NSSL & SBM microphysics schemes to understand the capability of bulk and bin schemes in simulating these events. Our results show that SBM (bin) scheme affects lightning flash events more accurately than the other two bulk schemes. Increasing aerosol concentrations, increases the cloud droplet number concentrations, thus influences the collision-coalescence processes thereby increase lightning activity over both regions. To further understand the influence of aerosol size, we used a spectral bin microphysics method with a dry radius range of (0.7nm-12µm), which modified the cloud microphysical features. Changing the number concentration and default size of aerosols also influenced the meteorology and hence the deep convection and thunderstorms occurring over the two selected case study regions. More results with greater details will be presented.

How to cite: Ghoshal Chowdhury, S., Ganguly, D., and Dey, S.: A modeling study on the role of aerosols in modulating the lightning flash rates over two different climatological regions of India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6397, https://doi.org/10.5194/egusphere-egu23-6397, 2023.

Cirrus clouds provide a significant radiative forcing on the Earth's climate system. The net cloud radiative forcing for cirrus clouds results a warming of the climate.  More/less cirrus clouds result in more/less warming of the planet. The moisture for the formation of cirrus clouds in the upper atmosphere is transported there in large part via deep convective storms, many associated with lightning activity and hence defined as thunderstorms.  An increasing in cirrus clouds in a warmer atmosphere will amplify the initial warming. This paper looks at the connection in space and time between monthly mean lightning activity observed from the Lightning Imaging Sensor on board the International Space Station (LIS-ISS), and the global monthly mean cirrus cloud cover obtained from the MERRA-2 reanalysis product. The correlation coefficient between the global monthly mean cloud optical thickness (COT) of the cirrus clouds (clouds at altitudes above the 400hPa pressure levels) with the monthly mean lightning flash counts is 0.84, implying that monthly mean  lightning can explain 70% of monthly variability of the global high cloud optical thickness. In addition, lightning amount explains nearly 60% of the monthly mean global area coverage of cirrus clouds.  Given these statistically significant connections between lightning and cirrus clouds, we propose using global lightning data as an additional tool for monitoring monthly variability of cirrus clouds.

How to cite: Saha, J., Price, C., and Guha, A.: The Role of Global Thunderstorm Activity in Modulating Global Cirrus Clouds, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13197, https://doi.org/10.5194/egusphere-egu23-13197, 2023.

Sea ice in the Arctic grows during each hemisphere’s winter and it retreats in the summer. The highly reflective white surface of sea ice reflects solar energy, cooling the planet. When it melts, the darker ocean absorbs more heat, reinforcing the cycle of melting sea ice. Sea ice plays a critical role in regulating Earth’s climate, and it influences global weather patterns and ocean circulations. One essential feedback in the Arctic is the rise in upper tropospheric water vapor (UTWV) or the specific humidity (SH) that acts as an intense greenhouse gas trapping in additional heat released from the Earth's surface.   While temperature change is driven by increasing greenhouse gases, the interannual variability in sea ice can be explained by changes in the UTWV (ASO) at 400mb in the Arctic. Where is this increase in UTWV (400mb) coming from in the Arctic?  Thunderstorm activity appears to be increasing in the Arctic in the last decades, and could be a source of the increasing UTWV, and hence the decrease in Arctic sea ice.

How to cite: Guha, A., Saha, J., and Price, C.: Increase in Lightning and Upper Tropospheric Water Vapour Over the Arctic Circle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14579, https://doi.org/10.5194/egusphere-egu23-14579, 2023.

During the last few years, DWD has developed a pioneering nowcasting procedure (NCS-A) for thunderstorms and strong convection based on  intelligent combination of lightning data, satellite information and Numerical Weather Prediction. The atmospheric motion vectors needed for the nowcasting are derived with the optical flow method TV-L1. Version 1 of the method NCS-A is operated 24/7 by DWD, covers the complete geostationary ring and has been very well received by aviation customers. The current developments of the nowcasting method focus on the analysis of life cycles in order to be able to improve the prediction of formation and decay of thunderstorms. This includes analysis of lightning activity. Further, work is also being done to seamlessly extend the forecast times by up to 6-8 hours through ensemble analysis of the Lightning Potential Index, provided by the DWD NWP model ICON. In addition to the mentioned developments of physical methods,  research is being also carried out on AI-based methods (neural networks) in cooperation with the University of Mainz. The presentation will start with an overview of the current 24/7 thunderstorm nowcasting. This will be followed by a presentation and discussion of the current developments at DWD aimed at providing accurate 6-8 hour forecasts of thunderstorms. Links for further readings and software will be provided as well.

_References: 

_{Müller R, Haussler S, Jerg M. The Role of NWP Filter for the Satellite Based Detection of Cumulonimbus Clouds. Remote Sensing. 2018; 10(3):386. https://doi.org/10.3390/rs10030386}

_{Urbich I, Bendix J, Müller R. Development of a Seamless Forecast for Solar Radiation Using ANAKLIM++. Remote Sensing. 2020; 12(21):3672. https://doi.org/10.3390/rs12213672.}

_{Müller R, Haussler S, Jerg M, Heizenreder D. A Novel Approach for the Detection of Developing Thunderstorm Cells. Remote Sensing. 2019; 11(4):443. https://doi.org/10.3390/rs11040443}

_{Zach, Christopher & Pock, Thomas & Bischof, Horst. (2007). A Duality Based Approach for Realtime TV-L1 Optical Flow. Pattern Recognition. 4713. 214-223. 10.1007/978-3-540-7}

_{Müller, R.; Barleben, A.; Haussler, S.; Jerg, M. A Novel Approach for the Global Detection and Nowcasting of Deep Convection and Thunderstorms. Remote Sens. 2022, 14, 3372. https://doi.org/10.3390/rs14143372}

_{Brodehl, S.; Müller, R.; Schömer, E.; Spichtinger, P.; Wand, M. End-to-End Prediction of Lightning Events from Geostationary Satellite Images. Remote Sens. 2022, 14, 3760. https://doi.org/10.3390/rs14153760} 

How to cite: Müller, R., Barleben, A., Haussler, S., and Jerg, M.: Short term forecast and monitoring of thunderstorms - status and recent developments at DWD., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1888, https://doi.org/10.5194/egusphere-egu23-1888, 2023.

We study evolution of lightning activity accompanying rapid intensity changes of tropical cyclones worldwide. We use a dataset of 400 tropical cyclones occurring between 2012 and 2017. We use the cyclones tracks from the International Best Track Archive for Clime Stewardship. The lightning data are provided by the World Wide Lightning Location Network (WWLLN). We inspect the lightning activity and median stroke energies accompanying rapid intensifications (RI) of cyclones, defined as increases of the wind speed by more than 30 kt in 24 hours, and their rapid weakenings (RW), defined as decreases of the wind speed by more than 40 kt in 24 hours.

In an area of radial wind maximum (RWM), we observe a stroke density of 15.1 strokes/(100 km)²/hour for RI and 21.8 strokes/(100 km)²/hour for RW, respectively, which is much higher than average RWM density 7.9 strokes/(100 km)²/hour over the duration of the cyclone. A median stroke energy is 0.3 kJ during RI and 0.7 kJ during RW. It means that during rapid intensification of cyclones, there are less strokes with slightly higher energies and during rapid weakening there are more strokes with slightly lower energies. When analyzing the cyclones in both hemispheres separately, we obtain 0.3 kJ for RI and 0.6 kJ for RW in the northern hemisphere, and 0.8 kJ for RI and 0.9 kJ for RW in the southern hemisphere. The difference in the stroke density during RI and RW was observed larger in the northern hemisphere (19.7 vs 34.1 strokes/(100 km)²/hour), when in the southern hemisphere the stroke density is much lower and differs less (4.4 strokes/(100 km)²/hour for RI and 5.1 strokes/(100 km)²/hour for RW).

How to cite: Rosická, K., Kolmašová, I., and Santolík, O.: Evolution of lightning activity observed during rapid intensity changes of tropical cyclones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6089, https://doi.org/10.5194/egusphere-egu23-6089, 2023.

Knowledge about the occurrence of thunderstorms in polar regions is still limited. Lightning detection systems have varying detection efficiency over time and space, which makes climatological analysis difficult. This is especially problematic in areas where lightning strikes are relatively rare. Traditional observations carried out at weather stations are therefore still a very important source of information about the occurrence of thunderstorms in the polar and circumpolar regions. Scientific studies usually predict that these phenomena will be more frequent in high latitudes in a warmer world. To check whether the number of thunderstorms changes as projected, we summarize SYNOP data from manned World Meteorological Organization (WMO) stations operating in the years 2000-2019 located at latitudes above 60° of both hemispheres. According to this source, the changes in thunderstorm frequency are only visible in certain areas and mostly during the summer months. The regional Kendall test revealed a statistically significant increase in the number of thunderstorm days north of 60°N in Interior Alaska, northwestern Canada, much of Siberia and European Russia. However, a decrease in thunderstorm frequency has also been detected in some regions. This was the case on the shores of the southern Norwegian Sea and seasonally in spring in the northern Urals. The largest increase in thunderstorm days exceeded 5 per decade in the highly continental regions of central Siberia and interior Alaska. For the entire high-latitude area, the change in the number of days with thunderstorms was statistically insignificant. However, the statistically relevant increase in the number of thunderstorm days is visible for inland weather stations located 250 – 1,000 km from the coastline, where it was on average 1 day per decade.

How to cite: Kępski, D. and Kubicki, M.: Changes in thunderstorm activity at high latitudes observed at WMO weather stations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-795, https://doi.org/10.5194/egusphere-egu23-795, 2023.

Far from being a recent development of the Earth System, volcanism has accompanied the Earth, terrestrial planets and countless exoplanets since their origins. Volcanism is a material mechanism whereby planets evolve to their differentiated states that are potentially capable of hosting life. Explosive volcanic eruptions are commonly accompanied by volcanic lightning, modulated by charging and discharging mechanisms within the eruption column. As discharges have been proposed as a potential prebiotic synthesis mechanism for forming first organic molecules, the behaviour of volcanic lightning at early Earth conditions could yield further insights into likely environments for the origin of life.

Earth´s atmosphere has changed significantly in composition and pressure since its early beginnings. Here, we would like to investigate how volcanic lightning might have operated and was influenced by changes in those environmental conditions. For this purpose, we have developed an experimental device, which consists of a gas-tight modification of a shock-tube apparatus, to investigate experimental discharges in decompressed jets of gas and volcanic ash particles under varying atmospheric conditions. The setup acts as a Faraday cage, capable of measuring discharges close to the vent. The gas inside the particle collector tank is sampled by crimp cap bottles and analysed by gas chromatography. We modified the enveloping atmospheric composition and pressure (200 mbar – 4 bar) and the transporting gas phase (argon and nitrogen).

We have tested atmospheres containing carbon dioxide, nitrogen and carbon monoxide to mimic early Earth conditions and obtained discharges with similar magnitude to those achieved in an air atmosphere. We have also varied the atmospheric pressure and observed that decreasing the atmospheric pressure results in less discharges. The results of the experiments demonstrate that it is the coupling between gas and ash particles which largely governs the occurrence and magnitude of discharges close to the jet nozzle. Nitrogen as transporting gas results in fewer discharges compared to argon, emphasizing the importance of the composition of the transporting gas phase in the jet charging and discharging mechanisms. The preliminary results point to active volcanic settings under varying atmospheric conditions as multivariate environment for the emergence of life and thus our experiments continue.  

How to cite: Springsklee, C., Scheu, B., Seifert, C., Cimarelli, C., Gaudin, D., Dingwell, D. B., and Trapp, O.: Experimental volcanic lightning under conditions relevant to the early Earth: Discharges as a possible prebiotic synthesis mechanism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1742, https://doi.org/10.5194/egusphere-egu23-1742, 2023.

Traditional long-range lightning detection and location networks use Time-of-Arrival (TOA) differences, and a single timestamp to locate lightning events. For long propagation distances, the amplitude of ground waves decays faster with distance than sky waves as a result of the ground conductivity and the effects of Earth curvature (Caligaris et al., 2008, Cooray, 2009, Hou et al., 2018). This can lead the skywaves to interfere with their large amplitudes when locating lightning.

Coherency, which is short for phase coherency of the analytic signal, is used here, which exhibits lightning characteristics (Bai & Fullekrug, 2022). This work introduces a simulation study to lay the foundation for new lightning location concepts. A novel interferometric method using coherency is presented here, which expands the use of more data points of recorded lightning sferics to map the lightning into an area in a long-range network. In this map, each pixel corresponds to a lightning location with different coherency and time of arrival differences, simulated by shifting the complex lightning waveforms. In long-range networks, the coherency of the 1st skywave is larger than the ground wave, and it is difficult to distinguish them due to the short time delay between them. One solution is to use a small network so that the recorded waveforms are associated with short propagation distances which can eliminate the interferences caused by the first skywave. Another solution is to filter the data such that a lightning waveform is represented by an impulse. In this case, only one maximum coherency area exists for each event at the lightning occurrence time.

In the future, the data collected with a real-time lightning detection network will be analysed to map the lightning events using the complex interferometric method for use in long-range lightning location networks.

References

Bai, X., & Füllekrug, M. (2022). Coherency of Lightning Sferics. Radio Sci., 57(5), e2021RS007347. doi: 10.1029/2021rs007347

Caligaris, C., Delfino, F., & Procopio, R. (2008). Cooray–Rubinstein Formula for the Evaluation of Lightning Radial Electric Fields: Derivation and Implementation in the Time Domain. IEEE Trans. Electromagn. Compat., 50(1), 194-197. doi: 10.1109/temc .2007.913226

Cooray, V. (2009). Propagation Effects Due to Finitely Conducting Ground on Lightning-Generated Magnetic Fields Evaluated Using Sommerfeld’s Integrals. IEEE Trans. Elec-tromagn. Compat., 51(3), 526-531. doi: 10.1109/temc.2009.2019759

Hou, W., Zhang, Q., Zhang, J., Wang, L., & Shen, Y. (2018). A New Approximate Method for Lightning-Radiated ELF/VLF Ground Wave Propagation over Intermediate Ranges. Int. J. Antennas Propag., 2018(6), 1-10. doi: 10.1155/2018/9353294

How to cite: Bai, X. and Fullekrug, M.: Long-range Lightning Interferometry (A Simulation Study), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6741, https://doi.org/10.5194/egusphere-egu23-6741, 2023.

Lightning is a ubiquitous source of infrasound, and an essential climate variable. Acoustic measurements have been carried out by the CEA over the last ten years to characterize thunder within the framework of the HyMeX project. First, during the fall of 2012 in the south of France in the Cévennes region during the intensive measurement campaign (SOP1) and more recently, in the fall of 2018 in Corsica (France), as part of the EXAEDRE campaign. During both the SOP1 and EXAEDRE campaigns, mini-arrays (“AA” for “Acoustic Array”) of four microphones (respectively disposed on a 50m and a 30m-wide triangle) were used. Lightning information were available thanks to three kinds of electromagnetic detection systems. Firstly, classical Lightning Location Systems (LLS) measured the low frequency range (1-350 kHz), giving the flash emission time and location, as well as its peak current. Secondly, a network of 12 antennas, Lightning Mapping Array (LMA), detecting in the very high frequency range (60-66 MHz) was used. It measured the radiation from leaders and intracloud discharges, which occur mostly inside the thundercloud, providing the 3D location of these discharges. Thirdly, the Charge Moment Change (CMC) was provided by broadband Extremely Low Frequency (< 1.1 kHz) measurements.

Time delays between AA sensors inform on the direction of sound arrival, while the difference between emission time and sound arrival provides the source distance. Combining the two allows a geometrical reconstruction of individual lightning flashes, each viewed as a set of point sound sources. Co-localization of acoustic sources with in-cloud detections provided by the LMA and with ground impacts provided by the LLS shows the efficiency and precision of the method. The measured sound amplitude can also be back-propagated, compensating for absorption and density stratification. This allows to evaluate the acoustical power of each detected source, and then the total power of an individual flash.

In both campaigns, very heterogeneous geometrical distributions of source sound powers within a single flash are frequently observed. Most of the power is frequently located in only one portion of the lightning, most of the time in the return stroke, but also sometimes in the intracloud part. A few homogeneous cases are observed, especially in SOP1. The total acoustical power of the flashes turns out to be also extremely variable, extending over at least 4 orders of magnitude with a median value of 3 MW. It correlates quite good with the peak current or the CMC, and the nature of the correlation differs strongly with the category of lightning considered, either typical return strokes or very energetic positive flashes generating sprites. However, a high dispersion of the data is observed, so that it is not possible to correctly predict any electrical parameter using only the total acoustic power of an event, although a trend is statistically observed. This could be overcome by finding other variables to fully explain the relationship between acoustical and electrical parameters, and improving our propagation model to better account for acoustic variability.

How to cite: Bestard, D., Farges, T., and Coulouvrat, F.: Localization and quantification of the acoustical power of lightning flashes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6342, https://doi.org/10.5194/egusphere-egu23-6342, 2023.

Global lightning location data has long been a critical tool for lightning research and safety. The Earth Networks Total Lightning Network (TLN) incorporates advanced lightning location technology delivering competitive lightning detection efficiency, location accuracy, and classification (intracloud vs cloud-to-ground). It consists of over 1800 wideband sensors deployed in 40+ countries to detect lightning and generate real-time localized storm alerts. TLN is constantly evolving through network expansion, as well as hardware and software development. In this presentation, we will cover some of the recent advances to the TLN hardware and processor. The new TLN sensor has been redesigned to use a dipole sensing element to help reduce the requirements of a strong ground. These new sensors are currently being used operationally and produce comparable waveforms to the previous monopole antenna. New upgrades to the lightning location algorithm have increased the detection efficiency, location accuracy, and classification accuracy of the network. Globally, TLN is locating approximately 50% more pulses than it was before. In moderately remote regions of the world, performance gains can be higher. TLN continues to use data from the World Wide Lightning Location Network (WWLLN), enhanced via raw signals from approximately 200 TLN sensors, to locate lightning in extremely remote regions like the deep oceans. However, how WWLLN data is incorporated into the TLN feed has changed, leading to significantly reduced false alarm rates in some regions. Location accuracy was improved by developing a new propagation model for signals produced by lightning, resulting in a reduction in location error by as much as a factor of 2. As a result of the improved location accuracy, as well as enhancements to the false alarms rates, there is improved clustering of lightning, which directly impacts downstream products such as lightning alerting and Dangerous Thunderstorm Alerts.

How to cite: DiGangi, E., Lapierre, J., Zhu, Y., and Stock, M.: Earth Networks Lightning System Update, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16886, https://doi.org/10.5194/egusphere-egu23-16886, 2023.

Lightning flashes can produce a discharge in which a continuing electrical current flows for more than 40 ms. Such flashes have been proposed to be the main precursors of lightning-ignited wildfires.

In this work, we used lightning measurements provided by the Geostationary Lightning Mapper (GLM) over the continental United States of America during the summer of 2018 to confirm the role of lightning with continuing currents in the ignition of wildfires. We investigated projections in the occurrence of lightning with continuing currents and in the meteorological conditions that favor wildfires over the next century by applying a new parameterization of continuing currents based on the updraft strength. The simulations are performed by using the European Center HAMburg general circulation (ECHAM) / Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model [1]. We found a 41% increase in the occurrence of lightning with continuing currents worldwide. Increases are largest in South America, the western coast of Northern America, Central America, Australia, Southern and Eastern Asia, and Europe, while only regional variations are found in northern polar forests, where wildfires can affect permafrost soil carbon release.

We obtained a possible increase in the risk of lightning-ignited fires in Europe, Eastern Asia, North America, the Western coast of South America, Central Africa and Australia. In turn, the simulations suggest a decrease in the risk of lightning-ignited wildfires in polar regions of Eurasia and North America. Finally, projections do not show any clear tendency in the Amazon rainforest during the typical fire season.

[1] Pérez-Invernón, F. J., Huntrieser, H., Jöckel, P., and Gordillo-Vázquez, F. J.: A parameterization of long-continuing-current (LCC) lightning in the lightning submodel LNOX (version 3.0) of the Modular Earth Submodel System (MESSy, version 2.54), Geosci. Model Dev., 15, 1545–1565, https://doi.org/10.5194/gmd-15-1545-2022, 2022.

How to cite: Pérez-Invernón, F. J., Gordillo-Vázquez, F. J., Huntrieser, H., and Jöckel, P.: Global occurrence of continuing currents in lightning and lightning-ignited wildfires predicted for the next century, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5302, https://doi.org/10.5194/egusphere-egu23-5302, 2023.

A presence of regular sequences of microsecond-scale pulses has been occasionally reported in the lightning literature for more than forty years. Due to a fine time resolution of modern electromagnetic receivers, the properties of these pulse trains are now well described. Nevertheless, the conditions for their occurrence are still not understood, and the information needed for their proper modelling is not sufficient.  

To contribute to this effort, we report for the first time properties of negative recoil stepped leaders accompanied by regular trains of microsecond-scale pulses simultaneously seen by the broadband magnetic loop antenna SLAVIA (Shielded Loop Antenna with a Versatile Integrated Amplifier; 5 kHz-90 MHz), and the radio telescope LOFAR (Low Frequency Array; 30-80MHz). We investigate four pulse trains that occurred during complicated intracloud flashes on 18 June 2021, when heavy thunderstorms hit Netherlands.

The pulses within the trains are unipolar, a few microseconds wide with an inter-pulse interval of about ten microseconds. The pulse trains last from 100 µs to 800 µs. After a careful time alignment of both magnetic field and LOFAR time series, we found that the broadband pulses perfectly match with regularly distributed and relatively isolated bursts of VHF sources localized by the LOFAR impulsive imager. All trains were generated by negative recoil stepped leaders propagating downward (two events) or upward (two events) at altitudes between 5.5 km and 8.5 km. Their tracks were formed by positive leaders occurring within the same flash several hundreds of milliseconds previously. The peak powers of VHF sources seen by the LOFAR electric antennas closest to the investigated discharges were about one order of magnitude higher than the power of signals emitted by normal negative leaders. These stepped recoil leaders propagate at a relatively low speed of about 2-5x10^6 m/s, when similar recoil leaders often reach speeds of 10^7 m/s. The velocity and inter-pulse intervals decrease towards the end of trains.

We show that observed pulse trains are due to stepping recoil leaders. However, we consider this strong pulsing nature of the examined recoil leaders to be quite unusual. The physical mechanism giving rise to the energetic VHF bursts and accompanying regular microsecond-scale pulses remains unclear.

How to cite: Kolmašová, I., Scholten, O., Santolik, O., Hare, B. M., Liu, N. Y., Dwyer, J. R., and Lán, R.: A strong pulsing nature of negative recoil leaders accompanied by regular trains of microsecond-scale pulses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3801, https://doi.org/10.5194/egusphere-egu23-3801, 2023.

We have used the LOw-Frequency ARray (LOFAR) to search for the growing tip of an intra-cloud (IC) positive leader. LOFAR is an extended astronomical radio telescope consisting of many (thousands antennas arranged is stations operating at very-high frequencies (VHF). For these lightning observations we have used about 170 dual polarized antennas in the Netherlands with baselines up to 100 km.  

Even with our most sensitive beamforming method, where we coherently add the signals of all 170 antenna pairs, we were not able to detect any emission from the tip of an IC positive leader. Instead, we put constraints on the emissivity of VHF radiation from the tip at 1 aJ/MHz at 60 MHz, well below the intensity of the galactic background.

We conclude that these IC positive leaders propagate in a continuous process which is in sharp contrast to what is seen to the step-wise propagation seen in some cloud-to-ground positive leaders and for negative leaders.

How to cite: Scholten, O., Hare, B., Dwyer, J., Liu, N., and Sterpka, C.: Searching for the VHF signature of the tip of an intra-cloud positive leader, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11504, https://doi.org/10.5194/egusphere-egu23-11504, 2023.

Lightning dart and recoil leaders are difficult to understand, as they have a different (often smoother) propagation mode than stepped leaders, and re-ionize a previously ionized channel. In order to understand them better, we have imaged recoil leaders with the LOFAR radio telescope (30-80 MHz), and will present 3D polarization, speed, and intensity data from multiple recoil leaders. We will show that many recoil leaders with high VHF intensity have VHF polarization that is very parallel to the recoil leader channel, with an opening angle as small as 15 degrees. Recoil leaders with lower VHF intensity have larger polarization opening angles, but it is not clear if this is physical or instrumental. In addition, VHF emission from recoil leaders comes from a sub-meter thin channel. Finally, we will show that the propagation speed and VHF intensity are strongly correlated; almost following a power-law or exponential relationship. These results probe the streamer behavior of recoil leaders, and thus provide significant clues to how recoil and dart leaders propagate. The fact that recoil leaders are very VHF thin is consistent with small polarization opening angles, and demonstrates that recoil leaders have significant streamer activity in their core and their corona sheath is VHF silent. The power-law/exponential relationship between speed and VHF intensity, however, is very difficult to explain.

How to cite: Hare, B., Scholten, O., Buitink, S., Dwyer, J., Liu, N., Sterpka, C., and ter Veen, S.: The propagation and 3D VHF polarization properties of recoil leaders, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12591, https://doi.org/10.5194/egusphere-egu23-12591, 2023.

Negative streamers play an important part in propagation of a negative stepped leader. They are emitted from the tip of a space stem or, as a streamer burst, from the tip of the space leader right after its attachment to the main leader.

In the laboratory conditions, it was shown that negative streamers need a significantly higher voltage for inception than positive streamers [e.g., Briels et al, 2008, doi:10.1088/0022-3727/41/23/234004]. The higher negative threshold is in agreement with the higher field measured inside streamer channels, namely 13±2 kV/cm for negative streamers versus 5 kV/cm for positive streamers.

We obtain the conditions for propagation of negative streamers using the Streamer Parameter Model (SPM) [Lehtinen, 2021, doi:10.1007/s11141-021-10108-5]. In this model, we calculate various streamer parameters from relationships between them, with the assumption of maximization of streamer velocity. This model, in the positive streamer case, was shown to agree well with both experimental measurements and hydrodynamic simulation results [Lehtinen and Marskar, 2021, doi:10.3390/atmos12121664]. In the negative streamer case, we show that the parameter equations have no solution below certain background electric fields. The threshold at which the negative streamer appears is around 12-14 kV/cm for 5-10 cm streamer length, which agrees with the experimental data. We also perform hydrodynamic simulations of negative streamers as another way to calculate the conditions for negative streamer propagation.

There is an important difference from positive streamers, for which the propagation threshold is determined by the rate of free electron removal from the streamer channel (i.e., attachment): namely, we find that the negative streamer threshold field is finite even in the absence of the electron removal.

How to cite: Lehtinen, N.: Conditions for inception and propagation of negative streamers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5529, https://doi.org/10.5194/egusphere-egu23-5529, 2023.

ELVES are transient ring-shaped emissions occurring in the ionosphere above thunderstorms. Multi-ELVES are events consisting of two and up to four rings of light separated temporally by tens of microseconds. The Fluorescence Detector (FD) at the Pierre Auger Observatory has been detecting ELVES with a dedicated trigger since 2013. The high temporal resolution of 100 ns of the FD allows us to record the phototraces of the events in great detail. From the improved processing of the phototraces, we have observed ELVES with double and triple peaks. In fact, during the period 2014-20, about 27% of the events detected at Auger are multi-ELVES. The origin of multi-ELVES is still not fully understood, therefore in this work, we tested two models: the first one relates the temporal difference between two peaks (ΔT) to the rise (t_r) and fall (t_f) times of the current density pulse of the source beam; the second one relates the height of the intra-cloud lightning source (h_b) to ΔT and is used to study events with three or more peaks. From the first model, we can obtain combinations of t_r and t_f where ΔT tends to zero, i.e. the origin of the simple ELVES can also be explained. For this analysis, we compare the ELVES parameters measured in Auger with the lightning properties detected by Earth Networks, i.e. the location, waveform, and height of these sources. 

How to cite: Vásquez Ramírez, A., Mussa, R., and Núñez, L. A. and the Pierre Auger Collaboration: Study of multiple ELVES at the Pierre Auger Observatory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7176, https://doi.org/10.5194/egusphere-egu23-7176, 2023.

The presence of transient corona discharges occurring in thunderclouds has been suspected for a long time. Thunderstorm coronas can be observed as Blue LUminous Events (BLUEs) formed by a large number of streamers characterized by their distinct 337 nm light flashes with negligible (or absent) 777.4 nm optical emission (typical of lightning leaders). The Modular Multispectral Imaging Array (MMIA) of the Atmosphere-Space Interaction Monitor (ASIM) has successfully allowed us to map and characterize BLUEs worldwide. The results presented here include a global analysis of key properties of BLUEs such as their characteristic rise times and duration, their depth with respect to cloud tops, vertical length and number of streamers. We present two different global annual average climatologies of BLUEs depending on considerations about the rise time and total duration of BLUEs worldwide [1-3].

We found that around 10 % of all detected BLUEs exhibit an impulsive single pulse 337 nm light curve shape. The rest of BLUEs are unclear (impulsive or not) single, multiple or with ambiguous pulse shapes. BLUEs exhibit two distinct populations with peak power density < 25 μWm⁻² (common) and ≥ 25 μWm⁻² (rare) with different rise times and durations. The altitude (and depth below cloud tops) zonal distribution of impulsive single pulse BLUEs indicate that they are commonly present between cloud tops and a depth of ≤ 4 km in the tropics and ≤ 1 km in mid and higher latitudes. Impulsive single pulse BLUEs in the tropics are the longest (up to about 4 km height) and have the largest number of streamers (up to approximately 3 × 10⁹).

[1] S. Soler, F. J. Pérez-Invernón, F. J. Gordillo-Vázquez, A. Luque, D. Li, A. Malagón-Romero, T. Neubert, O. Chanrion, V. Reglero, J. Navarro-González, G. Lu, H. Zhang, A. Huang, N. Ostgaard.: "Blue optical observations of narrow bipolar events by ASIM suggest corona streamer activity in thunderstorms" (Editor's Hightlight), Journal of Geophysical Research - Atmospheres, vol. 125, 2020, doi: 10.1029/2020JD032708.

[2] S. Soler, F. J. Gordillo-Vázquez, F. J. Pérez-Invernón, A. Luque, D. Li, T. Neubert, O. Chanrion, V. Reglero, J. Navarro-González, N. Ostgaard.: "Global Frequency and Geographical Distribution of Nighttime Streamer Corona Discharges (BLUEs) in Thunderclouds", Geophysical Research Letters 2021, 48, doi: 10.1029/2021GL094657.

[3] S. Soler, F. J. Gordillo‐Vázquez, F. J. Pérez‐Invernón, A. Luque, D. Li, T. Neubert, O. Chanrion, V. Reglero, J. Navarro-González, N. Østgaard.: "Global distribution of key features of streamer corona discharges in thunderclouds". Journal of Geophysical Research: Atmospheres, vol. 127, 2022, doi: 10.1029/2022JD037535.

How to cite: Gordillo-Vazquez, F. J., Soler, S., Pérez-Invernón, F. J., Luque, A., Li, D., Neubert, T., Chanrion, O., Reglero, V., Pérez-Navarro, J., and Ostgaard, N.: Worldwide distributions and key properties of Blue LUminous Events (BLUEs) as detected by ASIM, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2026, https://doi.org/10.5194/egusphere-egu23-2026, 2023.

The Atmosphere-Space Interactions Monitor (ASIM) on the International Space Station (ISS) observes lightning and Transient Luminous Events (TLEs) above the thunderstorm clouds. ASIM includes three photometers that sample at 100 kHz and two cameras that image at 12 frames per second. The photometers measure part of the far ultraviolet (FUV) and middle ultraviolet (MUV) band at 180 – 300 nm, a line of the second positive system of N₂ at 337nm (blue) and an atomic oxygen line at 777.4 nm (red). The cameras measure in the blue and red bands of the photometers with a spatial resolution on the ground around 400 m × 400 m. When ASIM is in a nadir-viewing configuration, photometer signals in the blue and red are sometimes associated with coincident UV signals, indicating that the UV photons originated from lightning discharges at cloud altitudes and not from the TLEs at higher altitudes. Here, we analyse the optical properties of these events by combining data from ASIM, the global lightning network GLD360, Lightning Mapping Arrays (LMAs) and NEXRAD radars. Of the 12 cases identified with such data coverage, 5 are Cloud-to-Ground (CG) and 7 are Intra-Cloud (IC) lightnings. The lightning leaders are located nearby the cloud top boundaries or partly exposed outside the cloud. Both the CG and IC lightnings are associated with the exposed lightning leaders. The 5 CG lightnings are identified as the “bolts from the blue”, and the 7 IC lightnings are “cloud-to-air” lightning. The altitudes of the sources vary from 5 km to 7 km for the CG lightnings and from 7 km to 15 km for the IC lightnings. The optical properties for the events, such as their irradiance, rise time and duration in the different optical bands are summarized and discussed. The results provide information that allows to estimate the global occurrence of “bolts from the blue” and “cloud-to-air” lightning.

How to cite: Li, D., Neubert, T., Chanrion, O., Husbjerg, L. S., Luque, A., Zhu, Y., Østgaard, N., and Reglero, V.: Optical properties of the shallow and exposed lightning discharges observed by ASIM, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9041, https://doi.org/10.5194/egusphere-egu23-9041, 2023.

Elves are produced when electromagnetic pulses from lightning interact with the lower parts of the ionosphere and are observed from space as expanding rings of light in the UV and visible optical bands. Elves are known to be associated with high peak current lightning. Using data from the Modular Multi-spectral Imaging Array (MMIA) instrument of the Atmosphere-Space Interactions Monitor (ASIM) payload, we search for observations of Elves when high peak currents (>70 kA) are detected by the global ground-based lightning detection network GLD360. We identify two types of events; high peak current detections associated with Elves, and high peak current detections not associated with Elves. To understand why some high peak current discharges do not generate observable Elves, we explore the number of lightning discharges and their peak currents leading up to the events. Preliminary results indicate that for current pulses with peak currents below 100 kA we observe a significant number of Elves, but this quantity depends on the lightning activity within 5 minutes before. Current pulses with peak currents above 120 kA nearly always produce Elves, regardless of the preceding lightning activity.

How to cite: Bjørge-Engeland, I., Østgaard, N., Marisaldi, M., Luque, A., Mezentsev, A., Lehtinen, N., Chanrion, O., Neubert, T., and Reglero, V.: Detections of high peak current lightning and observations of Elves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9415, https://doi.org/10.5194/egusphere-egu23-9415, 2023.

The Pierre Auger Observatory, the largest cosmic-ray detector in the world, has been
observing peculiar events which are very likely downward TGFs. Their experimental
signature and their time evolution are very different from those of a shower produced
by an ultra high energy cosmic ray. The TGF-like events happen in coincidence with
lightning and low clouds and their deposited energy at the ground is compatible with
that of a standard downward TGF with the source at few kilometers above the
ground. The surface detector (SD) of the Auger Observatory consists of 1660 water-
Cherenkov detectors (WCDs) spread over 3000 km² in the Argentinian pampa. The
WCD height of 1.2 m makes them highly sensitive to gamma rays and the large area
covered with SD allows us to sample the TGF beam from different points. The
timing shape of WCD signals can be very important to constrain different TGF source
models. Cold runaway from the high fields near the leader tips or relativistic
feedback produce the same energy spectrum but predict a different rise and fall of the
counts versus time, and they could produce a different angular distribution.
Comparisons between simulations and data will be shown.
Moreover, first results from a preliminary analysis of the available meteorological
data at the time of Auger TGF-like events will be presented. Little is known about the
TGF-producing storms. The characteristics of these thunderstorms are being
investigated by studying meteorological data in coincidence with upward TGFs. A
similar analysis is important to better understand downward TGF production
mechanisms and investigate if are the same as those producing upward TGFs.

How to cite: Colalillo, R., Dwyer, J., Smith, D. M., and Ortberg, J. and the Pierre Auger Collaboration: Studying downward TGFs with the largest ground array of gamma-ray detectors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15378, https://doi.org/10.5194/egusphere-egu23-15378, 2023.

In the first two years of ASIM operations from June 2018 till the end of 2019 486 TGFs have been observed, with a TGF rate of 0.84 per day. Their geographical distribution is consistent with the three main lightning chimneys Central America, Central Africa, and South East of Asia. Figure 1 displays the ISS footprint positions when the TGFs were detected.

Figure 1: ISS position for the 2018-2019 ASIM TGFs. Red circles marked those within 4 minutes of the previous TGF detected.

If the TGF occurrence follows a stochastic process (each TGF is not related to the next one), the time-difference distribution between a TGF detection and the next one should fit an exponential distribution. For a Δt < 4 minutes the number of TGFs following the exponential distribution is 16. Opposite we got 85 in groups of 2-3 TGFs displayed in Figure 1 in red circles. Analyzing the apparent strong discrepancy in the number of detection in less than 4 minutes (Figure 2) and the number derived from the exponential distribution is one of the motivations of this study.

We build a grid of variable dimension cell size to keep the same ISS observing time for each cell in a Monte Carlo code to simulate the TGF generation that has into account the frequency and the anisotropy distribution of the TGFs over the earth.

To preserve the total number of TGF observed in Δt < 4 minutes we need to add a parameter related to the “Storm Activity” defined as the time in a cell available to generate a TGF. The model fits observations when this parameter is 7%±1%. The good correlation between model/observation is displayed in Figure 2.

Figure 2: The predicted distribution of the TGF pairs (Orange) in 15s bins fits the observations (Blue).

The scope of this work is to check the adopted “Storm Activity” value using WWLLN sferics database as a good indicator of storm activity.

How to cite: Navarro-González, J., Connell, P., Eyles, C., Reglero, V., López, J. A., Montanyà, J., Marisaldi, M., Mezentzev, A., Lindanger, A., Sarria, D., Østgaard, N., Chanrion, O., Christiansen, F., and Neubert, T.: TGFs - "Storm Activity" relationship , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15876, https://doi.org/10.5194/egusphere-egu23-15876, 2023.

The Airborne Lighting Observatory for FEGS and TGFs (ALOFT)  is a field campaign focused on observing Terrestrial Gamma-ray Flashes (TGFs) and gamma-ray glows from thunderclouds. ALOFT will be flown on a NASA ER-2 research aircraft, flying at 20 km altitude, and the payload  includes:

1) Fly’s Eye GLM Simulator (FEGS), an array of imaging photometers as well as different wavelengths, and electric field change meters.
2) Lightning Instrument Package (LIP), giving three component electric field measurements.
3) Several gamma-ray detectors covering four orders of magnitude dynamic range in flux as well as the full energy range for TGF/gamma-ray glow detection.

ALOFT is scheduled for July 2023, with 50 flight hours based out of Florida.  Flying over thunderstorms in Central America and Caribbean, one of the most active TGF regions on the planet during the most optimal season, the ALOFT campaign will help us to answer the questions:

1) How and under what conditions are TGFs produced?
2) How extended in space and time are the gamma-ray glows?

To answer question 1), the ALOFT campaign will be supported by ground based radio measurements from different locations in Central America and Caribbean.

To answer question 2), with realtime downlink of data we will know when the ER-2 encounters gamma-ray glowing thunderclouds, and we will instruct the pilot to have the aircraft perform have repeated overflights over this cloud as long as the glow exists, to answer question 2).  This will also help us understand whether gamma-ray glows and TGFs are interrelated.

The full set of observational goals of ALOFT are:

1. Observe TGFs in one of the most TGF-intense regions on the planet.
2. Observe gamma-ray glows in thunderstorms and their relation to TGFs.
3. Perform International Space Station Lightning Imaging Sensor (ISS LIS) and Global Lightning Monitor (GLM) validation using improved suborbital instrumentation (including upgraded FEGS).
4. Evaluate new design concepts for next-generation spaceborne lightning mappers.
5. If relevant instrumentation is available, make measurements useful to advance convection science from a suborbital platform.

In this presentation we will give the status and plans for the ALOFT mission.

How to cite: Ostgaard, N., Marisaldi, M., Ullaland, K., Yang, S., Hasan Qureshi, B., Søndergaard, J., Mezentsev, A., Sarria, D., Lehtinen, N., Lang, T., Christian, H., Quick, M., Blakeslee, R., Grove, J. E., and Shy, D.: The ALOFT mission: a flight campaign for TGF and gamma-ray glow observations over Central America and the Caribbean in July 2023, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3116, https://doi.org/10.5194/egusphere-egu23-3116, 2023.

ELVEs are quickly expanding rings of light emissions excited in the lower ionosphere by the electromagnetic pulse of an electric discharge in a thundercloud. They are commonly observed from space platforms and have been reported in conjunction with other atmospheric-electricity events. One motivation to investigate ELVEs is that their signal may provide insight into the discharge that created them. Until now the modeling of ELVES has either relied on strong simplifications or on the Finite-Difference Time-Domain (FDTD) method to directly solve the Maxwell equations. One limitation of the latter is that non-axisymmetrical discharges (with a slanted channel or a non-vertical magnetic field for example) require computationally expensive, fully three-dimensional meshes, which makes parametric studies of the ELVE features slow and cumbersome.  We show here that elementary electromagnetic theory allows one to model ELVEs, even non-axisymmetrical ones, with sufficient accuracy at little computational cost. We then apply our methods to the parametric study of ELVE photometric waveforms as recorded by space-based instruments.

How to cite: Luque Estepa, A., Bjørge-Engeland, I., Li, D., Østgaard, N., and Marisaldi, M.: Investigating ELVE photometric waveforms with elementary electromagnetics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16046, https://doi.org/10.5194/egusphere-egu23-16046, 2023.

K-changes are step-like electrostatic field changes, which occur during the final part of cloud flashes or between the return strokes in cloud-to-ground discharges. We numerically solve the full set of Maxwell’s equations coupled to the electrostatic Poisson’s equation for a given thundercloud charge structure to model the K-changes. We simulate the K-changes by a sequential increase of conductivity of the decayed vertical channel. This process creates a current pulse which attenuates as it propagates downward. We show how the modeled linear charge densities and electric potentials connected to K-changes evolve in time. We successfully compare our model with the electric field measured by a flat-plate E-change antenna with a sensor having a decay time constant of 1 s, a bandwidth of 0.16 Hz –2.6 MHz, and a sampling rate of 5 MS/s. The experimental data used for comparison with our model were obtained at KSC Florida in 2011.

How to cite: Kaspar, P., Marshall, T., Stolzenburg, M., Kolmasova, I., and Santolik, O.: Electrodynamic model of K-changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3124, https://doi.org/10.5194/egusphere-egu23-3124, 2023.

  It is not new knowledge that whistler are always present in the ionosphere during the thunderstorms. The terrestrial ionosphere is mainly a plasma region which is very sensitive for different disturbances. A wide range of plasma instabilities can develop  in this region, which are often nonlinear processes and leading to the development of plasma turbulence.  Turbulence is one of the most universal events phenomena in nature. It plays a crucial role in the dynamics of the space plasma processes. The turbulence appears when some physical parameter exceeds a certain level. It can have place during strong thunderstorms. The ionosphere is sometimes treated as plasma physics laboratory with unique possibility to study fundamental plasma processes. The use of ionospheric satellite  gives the chance to perform insitu measurement of plasma parameters during dynamic processes. For our analysis we used set of selected data  of the electric and magnetic fields variations in ELF and VLF ranges originating from the all French microsatellite DEMETER which was operating on the circular orbit with inclination of about 80⁰ at altitude of 660 km from July 2004 until December 2010.

The  Fourier, wavelet and bispectral analysis of these signals has been performed. The 3 waves processes has been identified during few very strong strokes. In some cases the nonlinear interactions of whistlers with VLF signals of ground based transmitters. The character of spectra suggests the presence of Richardson’s cascade. Our conclusion is that these results are related to whistler turbulence.

How to cite: Blecki, J., Wronowski, R., and Jujeczko, P.: The nonlinear interactions of whistlers in the ionospheric plasma during strong thunderstorms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9989, https://doi.org/10.5194/egusphere-egu23-9989, 2023.

Terrestrial gamma-ray flashes (TGFs) are bursts of energetic X- and gamma-rays emitted from thunderstorms and observed by the Atmosphere-Space Interactions Monitor (ASIM) mounted onto the International Space Station (ISS) detecting TGFs and optical signatures of lightning. ISS-LIS (Lightning Imaging Sensor) detects lightning flashes allowing for simultaneous measurements with ASIM. Whilst ASIM measures ~300-400 TGFs per year, ISS-LIS detects ~ 10⁶ annual lightning flashes giving a disproportion of four orders of magnitude. Hence, based on the temporal evolution of lightning flashes and their spatial pattern, we present an algorithm to reduce the number of flashes potentially associated with TGFs by ~90%, and we use the ASIM TGF list to ensure that the resulting flashes are those associated with TGFs and thus benchmark our algorithm. We will compare how the radiance, footprint size and the global distribution of lightning flashes of the reduced set relates to the average of all measured lightning flashes. Finally, we will present a parameter study of our algorithm and discuss which parameters can be tweaked to maximize the reduction efficiency whilst keeping those flashes associated to TGFs. In the future, this algorithm will hence facilitate the search for TGFs in a reduced set of lightning flashes.

How to cite: Köhn, C., Heumesser, M., Chanrion, O., Reglero, V., Østgaard, N., Christian, H., Lang, T., Blakeslee, R., and Neubert, T.: Employing Optical Lightning Data to identify lightning flashes associated to Terrestrial Gamma-ray Flashes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1480, https://doi.org/10.5194/egusphere-egu23-1480, 2023.

As part of the Alpbach Summer School, a collaboration between FFG, ESA and ISSI, a team of students developed the F-class CASPER mission concept to investigate Transient Luminous Events (TLEs) and Terrestrial Gamma Ray Flashes (TGFs). These lightning-related plasma phenomena, first detected on Earth in 1989, typically occur in the mesosphere at an altitude between 50-100 km. The UVS instrument onboard the JUNO mission detected several similar events on Jupiter, and they are expected to also occur on other planets.

The CASPER mission consists of two identical spacecraft, each of which will be equipped with three cameras in different wavelengths and four high speed sensors, the latter will function as triggers to start the data acquisition of higher resolution images. A system chosen to combat the transient characteristic of the events (lifetime < 300 ms). While three sensors will be taking measurements of photons, one will quantify the electron flux in order to constrain the role of TLEs and TGFs in the global electric circuit.

The second great area of interest is the vertical structure of TLEs as well as their global distribution and occurrence rates. To achieve this, data will be captured using a two-satellite train in a sun-synchronous low earth orbit. The orbit is inclined at 98° and the satellites are phased at an angle of 5.2° to observe these events from two points of view simultaneously. The operational mission lifetime is five years, with a possible extension.

How to cite: Maurer, M., Byrne, L., Falk-Petersen, U., Hamdoun, A., Hénaff, G., Huber, K., Ilas, A., Reisinger, N., Sinjan, J., Suarez, C., Szilágy-Sándor, A., Tarvus, V., Tsindis, M., and Vaganov, M.: CASPER: A Space Mission Concept to Investigate Transient Luminous Events and Terrestrial Gamma Ray Flashes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12033, https://doi.org/10.5194/egusphere-egu23-12033, 2023.