Narrow Bipolar Events (NBEs) are brief intracloud (IC) discharge processes that generate powerful radiation in the HF and VHF radio bands. NBEs typically occur in isolation, but they have also been identified as initial events in IC lightning flashes. Their incidence is statistically correlated with the strength of convection. NBEs can exhibit both polarities and usually occur in the upper regions of the thundercloud. We present, for the first time, properties of NBEs detected in the Mediterranean region. The dataset comprises 37 events recorded by broadband magnetic loops located at two sites in France. The events were identified using the list of NBEs from 2022 provided by the Earth Network. The frequency range of our broadband sensors enabled us to obtain detailed shapes of NBE pulses. We calculated rise times, full width at half maximum times, and zero-crossing times of NBE pulses to facilitate comparisons with observations of NBEs in other parts of the world. The majority of NBE pulses observed in the Mediterranean region were isolated events occurring above the land and displaying a simple bipolar waveform with an overshoot peak of the opposite polarity. For two events, we supplemented our observation with the data from the SAETTA (Suivi de l’Activité Electrique Tridimensionnelle Totale de l’Atmosphère) lightning mapping array. Additionally, we estimated the altitude of the NBE events and placed our observations in the meteorological contexts to determine why NBE occurrences in the Mediterranean region have been overlooked until now.

About 45 lightning flashes occur per second all around the Earth with a predominant distribution over the continents and along the inter-tropical band. While different types of Transient Luminous Events (TLEs) induced by lightning flashes can be produced above the thunderstorms, Terrestrial Gamma Ray Flashes (TGFs) are bursts of high-energy photons originating from the Earth’s atmosphere in association with thunderstorm activity with a great majority of TGFs occurring in the inter-tropical region. In addition to those radiation bursts, another type of high-energy emission, so-called gamma ray glows, has been observed inside thunderstorms corresponding to significant enhancements of background radiation that last for more than a few seconds. All these connected phenomena remain to be documented both remotely and on an in-situ manner. Balloon-borne missions offer the required in-situ close-range high-altitude measurements of the ambient electrostatic field, conductivity, TGF radiation and lightning occurrence for a better understanding and modeling of these complex phenomena and of their effects on the Earth atmosphere and the global atmospheric electrical circuit.The STRATELEC (STRatéole-2 ATmospheric ELECtricity) project (Defer et al., 2022), funded by CNES, aims at deploying within the Stratéole-2 framework (Hertzog and Plougonven, 2020) new atmospheric electricity instrumentation on several stratospheric balloons to:Document the electrical state of the atmosphere and the production of high-energy radiation through in-situ and remote sensing measurements to reach better understanding and better modeling capabilities of the processes occurring during thunderstorms, Identify state-of-the-art and emerging technologies to populate the STRATELEC instrumentation package with new sensors in the perspective of their operation on stratospheric balloons, high altitude aircraft and even low-level drones to eventually propose new balloon and/or space mission concepts, Contribute to additional scientific returns on any space mission dedicated to lightning detection (e.g. MTG-LI, GOES-GLM) and more generally to the study of the convection in the Tropics and of electrodynamic couplings in the terrestrial atmosphere-ionosphere-magnetosphere system. First, we will remind the scientific objectives of the STRATELEC project. Then we will provide an update on the different scientific and technical activities, including the development and the testing of STRATELEC instruments, but also the data analysis méthodology. Finally, we will discuss the way forward for the upcoming and final Stratéole-2 campaign (winter 2026-2027), as well as some initial thoughts on future balloon campaigns. Hertzog A., and R. Plougonven (2020), Stratéole-2 : des ballons longue durée pour étudier la tropopause tropicale, La Météorologie - n° 108 - février 2020.Defer, E., et al. (2022), An Overview of the STRATELEC (STRatéole-2 ATmospheric ELECtricity) Project, 25th ESA Symposium on European Rocket and Balloon Programmes and Related Research, 1-5 May 2022, Biarritz, France.

The Athena mission entered a redefinition phase in July 2022, driven by the imperative to reduce the mission cost at completion for the European Space Agency below an acceptable target, while maintaining the flagship nature of its science return. This notably called for a complete redesign of the X-ray Integral Field Unit (X-IFU) cryogenic architecture towards a simpler active cooling chain. Passive cooling via successive radiative panels at spacecraft level is now used to provide a 50 K thermal environment to an X-IFU owned cryostat. 4.5 K cooling is achieved via a single remote active cryocooler unit, while a multi-stage Adiabatic Demagnetization Refrigerator ensures heat lift down to the 50 mK required by the detectors. Amidst these changes, the core concept of the readout chain remains robust, employing Transition Edge Sensor microcalorimeters and a SQUID-based Time-Division Multiplexing scheme. Noteworthy is the introduction of a slower pixel. This enables an increase in the multiplexing factor (from 34 to 48) without compromising the instrument energy resolution, hence keeping significant system margins to the new 4 eV resolution requirement. This allows reducing the number of channels by more than a factor two, and thus the resource demands on the system, while keeping a 4' field of view (compared to 5' before). In this article, we will give an overview of this new architecture, before detailing its anticipated performances. Finally, we will present the new X-IFU schedule, with its short term focus on demonstration activities towards a mission adoption in early 2027.

Thunderclouds and lightning produce high-energy radiation over a wide range of time scales. Terrestrial gamma-ray flashes (TGFs) are brief emissions lasting ~100 µs, consisting of photons with energies ranging from 20 keV to 40 MeV. Simultaneous ground-based measurements of electromagnetic fields and gamma-ray emissions have found TGFs to be associated with the evolutionary phases of both intracloud and cloud-to-ground lightning discharges.Gamma-ray glows, on the other hand, last from a few seconds to several tens of minutes, typically coincide with the passage of thunderclouds, and are sometimes abruptly terminated by nearby lightning. Photons emitted during gamma-ray glows share the same energy spectrum as TGFs but are less intense. It was recently discovered that thundercloud regions can glow for hours and that gamma glows are more dynamic phenomena than originally thought.Both types of gamma-ray emissions are believed to be generated via bremsstrahlung by energetic runaway electrons accelerated in the strong electric fields within thunderclouds. However, the connection between TGFs and gamma-ray glows remains not fully understood.Until now, the only simultaneous gamma ray and radio wave measurements were conducted onboard an airplane during the ALOFT campaign. The TARANIS mission, which was intended to carry a unique set of electromagnetic, particle, gamma ray, and optical instruments, was unfortunately lost due to the failure of the Vega launcher in 2020.The STRATELEC balloon project (part of the French-US STRATEOLE-2 project of long-duration balloon flights at the tropical tropopause), with precise synchronization of broadband electric field measurements and a gamma-ray detector, will provide a unique opportunity to correlate individual photon detections with electromagnetic pulses emitted by various lightning processes. These coordinated measurements could help answer the following questions:a) At which stage of the evolution of lightning discharges are TGFs produced? b) Which types of intracloud discharges produce detectable high-energy radiation? c) What are the differences in the electromagnetic signatures of lightning processes associated with TGFs and gamma glows? d) What are the temporal variations in electromagnetic emissions associated with gamma glows? e) Are flickering TGFs truly radio silent? In this presentation, we introduce the FPGA-based radio receiver RIP (Radio Instrument Package), developed for the STRATELEC balloon project. The receiver is designed to capture and analyze the electromagnetic signatures of various lightning phenomena associated with gamma-ray production, including leader pulses, initial breakdown pulses, compact intracloud discharges, and dart-stepped leader pulses. The anticipated launch is late 2026.

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum V capability of 600 ms^-1 . Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule.

In this overview, we underscore the significance of conducting broadband electromagnetic measurements to study the initiation and progression of lightning discharges within thunderclouds. Using a newly developed shielded magnetic loop antenna sensitive to frequencies ranging from 5 kHz to 90 MHz we enhanced our understanding of the initial phase of negative cloud-to-ground lightning discharges. Through the integration of broadband recordings with data obtained from narrowband lightning mapping arrays, we have unveiled the origins of rarely occurring microsecond-scale pulse trains in electromagnetic recordings and provided a detailed description of behaviour of attempted lightning leaders. Our findings also demonstrate that lightning can serve as a valuable tool for investigating the thundercloud charge structure, particularly when electromagnetic data sets are complemented with meteorological radar measurements.

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.

Our knowledge about the fine structure of lightning processes at Jupiter was substantially limited by the time resolution of previous measurements. Recent observations of the Juno mission revealed electromagnetic signals of Jovian rapid whistlers at a cadence of a few lightning discharges per second, comparable to observations of return strokes at Earth. The duration of these discharges was below a few milliseconds and below one millisecond in the case of Jovian dispersed pulses, which were also discovered by Juno. However, it was still uncertain if Jovian lightning processes have the fine structure of steps corresponding to phenomena known from thunderstorms at Earth. Here we show results collected by the Juno Waves instrument during 5 years of measurements at 125-microsecond resolution. We identify radio pulses with typical time separations of one millisecond, which suggest step-like extensions of lightning channels and indicate that Jovian lightning initiation processes are similar to the initiation of intracloud lightning at Earth.

Our study aims at initial stage of energetic negative cloud-to-ground (CG) winter lightning flashes. We analyze broadband magnetic-field measurements recorded in the West Mediterranean region in winter 2014/2015. By combining our data with information provided by the French national lightning locating system MÉTÉORAGE, we were able to select 200 waveform captures, which contained return stroke (RS) pulses emitted by negative CG discharges with peak currents exceeding 100 kA. The frequency band of our instrumentation (5 kHz-90 MHz) allowed us to investigate fine details of recorded waveforms. We found that the winter pre-stroke processes were very short, lasting on average only 1.7 ms from the first bipolar preliminary breakdown (PB) pulse to the following return stroke pulse. The amplitudes of the strongest PB pulses reached on average only 25 % of the corresponding RS pulse. We investigate the evolution of peak amplitudes and inter-pulse intervals of PB pulses within individual PB trains. We found that in some trains the amplitudes of pulses were nearly monotonically increasing with time, they reached a maximum in a few hundreds of microseconds, and then decreased again being relatively regularly distributed in time. Within other PB trains, the pulses were chaotically spaced and their peak amplitudes did not show any trend. We assume that the short duration of the pre-stroke process indicate strong electric fields inside winter thunderclouds and hypothesize that the time evolution of PB pulse amplitudes and interpulse intervals reflect the spatial arrangement of the negative charge region.

All evolution stages of cloud-to-ground (CG) lightning flashes, both positive (+CG) and negative (-CG), generate electromagnetic radiation, which can be used for their investigation. We focus on the electromagnetic activity immediately following the first return stroke (RS). We combine measurements of the broadband receiver BLESKA and the lightning mapping array (LMA) network SAETTA, capable of detecting sources of narrowband very high frequency (VHF) radiation. The French lightning location system Météorage provided us with the information about 2D location, polarity and peak currents for studied CG and intracloud (IC) discharges. From our data collected in the northwestern Mediterranean region from September to December 2015, we have selected and investigated the electromagnetic activity following 16 +CG and 38 -CG flashes. Using the data from individual SAETTA stations we found that 36 -CG flashes exhibited a fast decrease in the counts and in the power of VHF radiation sources immediately after the RS pulse. The maximum count of 2000 VHF radiation sources was detected by the closest SAETTA station at an average time delay of 66 μs after the RS pulse peak. At a delay of 1.85 ms after the RS pulse peak or sooner, the VHF radiation rate decreased below 1500 VHF radiation sources, with the median value of this time equal to 195 μs, and kept decreasing. In the case of all inspected +CG flashes, we observed an unexpectedly fast increase in the counts of the VHF radiation sources and their power after the RS pulse. Up to 161.95 ms after the RS pulse, the VHF radiation rate decreased below 1500 VHF radiation sources, with the median value of this time equal to 34.53 ms, much longer than in case of –CGs. At the same time, we observed a visible sequence of bipolar pulses lasting up to 50 ms in the magnetic-field waveforms recorded by BLESKA, with the amplitude of the biggest pulse varying from 2 to 10 nT. This observed longer presence of VHF radiation after +CG flashes may be caused by a potential difference between the end of neutralized RS channel and the positive charge layer in the thundercloud in case of +CGs, which might result in a new electrical breakdown. Then a stepwise propagation of a new negative leader inside the thundercloud is possible, emitting electromagnetic radiation in a wide range of frequencies. This radiation can be detected by narrowband LMA stations in the form of VHF radiation sources, same as by a broadband receiver in the form of pulses.

Two long-lasting thunderstorm ground enhancement (TGE) events were registered at the Milešovka meteorological observatory in Czechia (50.55∘ N, 13.93∘ E; 837 m altitude) on 23 April 2018, during linearly organized thunderstorms. Two intervals of increased photon counts were detected by a plastic scintillator, respectively lasting 70 and 25 min and reaching 31 % and 48 % above the background radiation levels. Using numerical simulations, we verified that the observed increases in count rates are consistent with the energy spectrum of previously observed TGEs. We investigated the relevant data from a suite of meteorological instruments, a Ka-band cloud radar, an electric field mill, and a broadband electromagnetic receiver, all placed at the Milešovka observatory, in order to analyse the context in which these unique continental TGEs occurred at an exceptionally low altitude. The onset of the TGEs preceded the onset of precipitation by 10 and 3 min, respectively, for the two events. Both this delayed rain arrival and an energy threshold of 6.5 MeV for registered particles clearly exclude the detection the decay products of the radon progeny washout during the TGE intervals. At the same time, the European lightning detection network EUCLID detected numerous predominantly negative intracloud lightning discharges at distances closer than 5 km from the particle detector, while the occurrence of cloud-to-ground discharges was suppressed. The cloud radar recorded presence of graupel below the melting level, and the composition of hydrometeors suggested good conditions for cloud electrification. The observed variations in the near-surface electric field were unusual, with very brief negative-electric-field excursions reaching −20 kV in a quick succession. At the same time, sub-microsecond unipolar pulses emitted by close corona discharges saturated the broadband magnetic loop antenna. All these measurements indicate that a strong lower positive-charge region was present inside the thundercloud. The bottom thundercloud dipole was probably responsible for acceleration of the seed electrons in the air. These seed electrons might originate in the secondary cosmic ray particles but could also come from a high concentration of radon in the air collected during the propagation of the convective system above the uranium-rich soils before the thunderstorms overpassed the Milešovka observatory.

Bursts of gamma rays observed on the Earth’s surface – so called Thunderstorm Ground Enhancements (TGE) were detected by a plastic scintillator (disassembled from the particle detector SEVAN) located in the observatory building on the Milešovka peak (50.6N, 13.9E, altitude 837 m) in Czechia. The TGEs observed during two thunderstorms on 23 April 2018 respectively lasted 65 and 15 minutes and exceeded the background radiation levels by 30 and 40 percent. The first storm was a part of an evolving squall line which crossed the Milešovka peak. The second storm was probably a supercell, which moved near Milešovka but did not hit its top. Both storms caused heavy precipitation and strong wind gusts. The onset of the TGEs preceded the onset of precipitation by approximately 8 minutes. During the increases of TGE radiation, the European lightning detection network EUCLID detected numerous predominantly negative intracloud lightning discharges at distances closer than 5 km from the particle detector. To understand the conditions for the TGE observation we investigated the data collected during the enhancements by a Ka-band cloud radar, an electric field mill, and a broadband electromagnetic receiver installed in the Milešovka peak observatory. Using the cloud radar measurements, we estimated the vertical extent of the thunderclouds. The cloud base was found at about 500 m above the observatory. Estimated heights of the cloud tops for the two storms were 12 and 8 km, respectively, indicating that the storm center of the second storm was not directly above the cloud radar. The updraft velocities reached 10 m/s. A composition of hydrometeors suggested good conditions for cloud electrification. We have found that the increases of TGE radiation corresponded to the large negative electric fields (up to – 20 kV/m) measured by the electric field mill rather than to individual discharges. We also identified numerous microsecond-scale pulses in the broadband magnetic field records, which can be attributed to corona-type discharges occurring near the receiving antenna in high local electric fields below the thunderstorm. Based on our analysis we assume that observed TGEs corresponded to the bremsstrahlung generated during collisions of electrons accelerated in the thunderstorm electric field with the air molecules. Because of a very small number of cloud-to-ground lighting discharges we hypothesize that the electrons might have been accelerated by a strong lower positive charge center at the bottom of the thundercloud. As the TGE radiation increases were unusually long, we speculate that their later part might have been assigned to the radon progeny which was lifted to the atmosphere by a near-surface electric field and returned back to the ground with the rain precipitation.

Ozone is a very important trace gas in the stratosphere and, thus, we need to know its time evolution over the globe. However, ground-based measurements are rare, especially in the Southern Hemisphere, and while satellite observations provide broader spatial coverage generally, they are not available everywhere. On the other hand, reanalysis data have regular spatial and temporal structure, which is beneficial for trend analysis, but temporal discontinuities might exist in the data. These discontinuities may influence the results of trend studies. The aim of this paper is to detect discontinuities in ozone data of the following reanalyses: MERRA-2, ERA-5 and JRA-55 with the help of the Pettitt, the Buishand, and the Standard Normal Homogeneity tests above the 500 hPa level. The share of discontinuities varies from 30% to 70% and they are strongly layer dependent. The share of discontinuities is the lowest for JRA-55. Differences between reanalyses were found to be larger than differences between homogeneity tests within one reanalysis. Another aim of this paper is to test the ability of homogeneity tests to detect the discontinuities in 2004 and 2015, when changes in versions of satellite data took place. We showed the discontinuities in 2004 are better detected than those in 2015.

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

The Radio and Plasma Wave instrument (RPW) for Solar Orbiter includes a Time Domain Sampler sub-unit (TDS) designed to capture electromagnetic waveform measurements of high-frequency plasma waves and antenna voltage spikes associated with dust impacts. TDS will digitize three components of the electric field and one magnetic component at 524 kHz sampling rate and scan the obtained signal for plasma waves and dust impact signatures. The main science target of TDS are Langmuir waves observed in the solar wind in association with Type II and Type III solar bursts, interplanetary shocks, magnetic holes, and other phenomena. In this poster, we present the scientific data products provided by the TDS instrument and discuss the first data obtained during the commissioning phase. The first data will be used to evaluate the actual performance of the RPW TDS instrument.

A broad-band analyzer of the IME-HF instrument (“Instrument de Mesure du champ Electrique Haute Frequence”) is prepared for the TARANIS (Tool for Analysis of RAdiation from lightNIng and Sprites) micro-satellite of the French space agency CNES. The spacecraft is based on the MYRIADE series platform. It will be launched on a Sun synchronous polar orbit at 700 km altitude. TARANIS will carry a complex payload of six scientific instruments to study radiation from lightning and optical phenomena (Transient Luminous Events) observed at altitudes between 20 and 100 km (blue jets, red sprites, halos, elves). The scientific instruments onboard TARANIS will detect electromagnetic radiation from very low frequencies up to 37 MHz, optical radiation, X rays (with an aim to study the Terrestrial "Gamma-ray" Flashes), and energetic electrons. The IME-HF instrument will record waveform measurements of fluctuating electric fields in the frequency range from a few kHz up to 37 MHz, with the following scientific aims: (i) Identification of possible wave signatures associated with transient luminous phenomena during storms; (ii) Characterization of lightning flashes from their HF electromagnetic signatures; (iii) Identification of possible HF electromagnetic or/and electrostatic signatures of precipitated and accelerated particles; (iv) Determination of characteristic frequencies of the medium using natural waves properties; (v) Global mapping of the natural and artificial waves in the HF frequency range, with an emphasis on the transient events. The instrument will be also able to trigger and record interesting intervals of data using a flexible event detection algorithm.