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The Atmosphere-Space Interactions Monitor (ASIM) was designed to monitor Terrestrial Gamma-ray Flashes (TGFs) and Transient Luminous Events (TLEs) from space, enabling the study of how these phenomena are related. In this paper, we present observations of 17 TGFs with accompanying Elves. TGFs are short and highly energetic bursts of gamma photons associated with lightning discharges, whereas Elves are TLEs that are observed as concentric rings of ultraviolet (UV) and visible light at ionospheric altitudes, produced by the excitation of N2 molecules when an electromagnetic pulse (EMP) hits the base of the ionosphere. Elves were identified when optical detections in the UV band could be clearly distinguished from other optical signals from lightning strokes. The TGFs they accompanied had short durations and were associated with particularly high peak current lightning. Lightning sferics associated with these events were detected by the global lightning network GLD360 and the World Wide Lightning Location Network (WWLLN), and they were, with the exception of one event, observed over ocean or coastal regions. It is likely that these events were associated with Energetic In-cloud Pulses (EIPs). We show that short duration TGFs tend to be associated with higher peak currents than long duration TGFs.

The Atmospheric Space Interactions Monitor (ASIM) was launched in 2018, and has since then observed Terrestrial Gamma-ray Flashes (TGFs) and Transient Luminous Events (TLEs). ASIM consists of the Modular X- and Gamma-ray Sensor (MXGS) and the Modular Multispectral Imaging Array (MMIA). Using data from both MXGS and MMIA, we investigate observations of TGFs (detected by MXGS) with accompanying elves (detected by MMIA). We study the optical signatures of the elves detected by a photometer of MMIA operating in the 180-230 nm band. Lightning sferics associated with these events have been detected by WWLLN and GLD360. Several TGFs have associated lightning sferics outside the field of view of MMIA, but due to the expanding rings of the elves we can still observe optical signatures from accompanying elves. Using GLD360 data we also study properties of the lightning strokes.

We investigate and determine the sequence of the Terrestrial Gamma-ray Flashes (TGFs) and the observed optical emissions associated with lightning flashes, as well as the connection between the duration of TGFs and the time between the onset of the TGFs and the observed main optical pulses. Over 200 observations from the instruments of the Atmosphere-Space Interactions Monitor (ASIM) on board the International Space Station (ISS) are used, together with data from the lightning detection networks GLD360 and WWLLN. The ASIM data consist of two separate recordings: High energy measurements from the Modular X- and Gamma-ray Sensor (MXGS), and optical measurements from the Modular Multi-Spectral Imaging Array (MMIA). The optical measurements are from photometers operating in the 337 and 777.4 nm bands, and the temporal uncertainty between the two instruments of ASIM is +- 5 µs.

Terrestrial Gamma-ray Flashes (TGFs) are sub-millisecond bursts of high-energy photons associated with lightning flashes in thunderstorms. The Atmosphere-Space Interactions Monitor (ASIM), launched in April 2018, is the first space mission specifically designed to detect TGFs. We will mainly focus on data from the High Energy Detector (HED) which is sensitive to photons with energies from 300 keV to > 30 MeV, and include data from the Low Energy Detector (LED) sensitive in 50 keV to 370 keV energy range. Both HED and LED are part of the Modular X- and Gamma-ray Sensor (MXGS) of ASIM.The energy spectrum of TGFs, together with Monte Carlo simulations, can provide information on the production altitude and beaming geometry of TGFs. Constraints have already been set on the production altitude and beaming geometry using other spacecraft and radio measurements. Some of these studies are based on cumulative spectra of a large number of TGFs (e.g. [1]), which smooth out individual variability. The spectral analysis of individual TGFs has been carried out up to now for Fermi TGFs only, showing spectral diversity [2]. Crucial key factors for individual TGF spectral analysis are a large number of counts, an energy range extended to several tens of MeV, a good energy calibration as well as knowledge and control of any instrumental effects affecting the measurements.Thanks to ASIM’s large effective area and low orbital altitude, single TGFs detected by ASIM have much more count statistics than observations from other spacecraft capable of detecting TGFs. By comparing Monte Carlo simulations to the energy spectrum from single ASIM TGFs we will aim to put stricter constraints on the production altitude and beaming geometry of TGFs. We will present the dataset, method, and some results of the spectral analysis of individual TGFs.References:1. Dwyer, J. R., and D. M. Smith (2005), A comparison between Monte Carlo simulations of runaway breakdown and terrestrial gamma-ray flash observations, Geophys. Res. Lett., 32, L22804, doi:10.1029/2005GL023848.2. Mailyan et al. (2016), The spectroscopy of individual terrestrial gamma-ray flashes: Constraining the source properties, J. Geophys. Res. Space Physics, 121, 11,346–11,363, doi:10.1002/2016JA022702.

We present a sample of Terrestrial Gamma-ray Flashes (TGFs) observed at mid latitudes by the Atmosphere Space Interaction Monitor (ASIM). The events were detected over the period June 2018 - August 2020 in the latitude bands between 35° and 51° and between -35° and -51°; the sample includes the first observations above ±38°. The characteristics of these mid-latitude events are consistent with the global population concerning the number of counts, but durations are significantly shorter. We also analyze the meteorological context and the general evolution of the parent storms and we show that the storms are not extreme in terms of total duration and extension. Finally, we present an estimation of the TGF occurrence rate at mid latitudes, based on ASIM's exposure, the local flash rate and tropopause altitude, and we show that it is outside but very close to two standard deviation from the rate of production at tropical latitudes, corrected by the higher atmospheric absorption of higher latitudes. This means that atmospheric absorption plays a major role in the detection of TGFs at mid latitudes, but we cannot rule out other factors.

The Atmosphere-Space Interactions Monitor (ASIM) is the first instrument in space specifically designed to observe terrestrial gamma-ray flashes (TGFs). TGFs are high energy photons associated with lightning flashes and we perform the spectral analysis of 17 TGFs detected by ASIM. The TGF sample is carefully selected by rigorous selection criteria to keep a clean sample suitable for spectral analysis, that is, suitable count statistics, low instrumental effects, and reliable source location. Monte Carlo modeling of individual TGFs has been compared to the observed energy spectra to study the possible source altitudes and beaming geometries. A careful model of the instrumental effects has been developed and validated. Several combinations of source altitudes and beaming geometries are accepted by the statistical tests for all the TGFs in the sample resulting in a large uncertainty in the estimate of the intrinsic source luminosity. The analyzed TGFs show significant variations in observed fluence independent of the distance between source and ASIM. A lower limit on the maximum photon energy produced by TGFs is estimated to be 24 MeV for the analyzed TGFs. The intrinsic limitations of TGF spectral analysis from space are also investigated and it is found that the ability to constrain the source altitude and beaming geometries of TGFs strongly depends on the distance between source and satellite. With the current generation of instruments with effective areas in the range of few hundreds cm2, it is very difficult to constrain reliably the source properties without the help of simultaneous measurements in the radio band. publishedVersion

We present a sample of Terrestrial Gamma-ray Flashes (TGFs) observed at mid latitudes by the Atmosphere Space Interaction Monitor (ASIM). The events were detected between June 2018 and August 2020 in the latitude bands between 35° and 51° in both hemispheres, which we hereafter refer to as “mid latitudes.” The sample includes the first observations above urn:x-wiley:2169897X:media:jgrd57293:jgrd57293-math-0001 and consists of 14 events clustered in four geographical regions: north-west Atlantic and eastern USA; Mediterranean Sea; the ocean around South Africa; and north-eastern China and Siberia. We examine the characteristics of each event, both standalone and in the context of the global ASIM TGF data set, and we find that our sample is consistent with the global population concerning the number of counts, but shows significantly shorter durations. We analyze the meteorological context and the general evolution of the parent storms and we show that the storms are not extreme in terms of total duration and extension. Whenever possible, we also include the radio sferics and the peak current of the parent stroke. Finally, we present an estimation of the TGF occurrence rate at mid latitudes, based on ASIM's exposure, the local flash rate and tropopause altitude, and we show that it is outside but very close to two standard deviation from the rate of production at tropical latitudes, corrected by the higher atmospheric absorption of higher latitudes. This means that atmospheric absorption plays a major role in the detection of TGFs at mid latitudes, but we cannot rule out other factors. publishedVersion

On February 8, 2019 the Atmosphere-Space Interaction Monitor (ASIM) passed a thunderstorm system north east of Puerto Rico and observed a TGF and an Elve from the same lightning stroke at the very beginning of a lightning flash. A second Elve was observed 456 ms later but without any signature of a TGF about 300 km south-east of the first Elve. The strokes associated with the two Elve events were detected by WWLLN and Vaisala, which allows for an absolute timing accuracy of the ASIM measurements of at least 100 us. Images of the lighting strokes support the source locations for the Elves and TGF. Both the rise time of the UV pulse by ASIM MMIA photometer and radio measurements from Puerto Rico indicate that the first stroke was an intracloud positive while the latter was a cloud-to-ground stroke. The UV emissions from the Elves preceded the optical emissions in 777 nm by50 us and 90 us, respectively. This can partly be explained by the scattering of 777 nm within the cloud. Current moments derived from radio measurements at Puerto Rico and Duke University indicate a fast (30 us) and large (200 kA) current pulse emitting an electromagnetic wave that produces an Elve and a slow (1-2 ms) current producing the optical signals.

Terrestrial Gamma-ray Flashes (TGFs) are sub milliseconds bursts of high energy photons associated with lightning flashes in thunderstorms. The Atmosphere-Space Interactions Monitor (ASIM), launched in April 2018, is the first space mission specifically designed to detect TGFs. We will mainly focus on data from the High Energy Detector (HED) which is sensitive to photons with energies from 300 keV to > 30 MeV, and include data from the Low Energy Detector (LED) sensitive in 50 keV to 370 keV energy range. Both HED and LED are part of the Modular X- and Gamma-ray Sensor (MXGS) of ASIM.The energy spectrum of TGFs, together with Monte Carlo simulations, can provide information on the production altitude and beaming geometry of TGFs. Constraints have already been set on the production altitude and beaming geometry using other spacecraft and radio measurements. Some of these studies are based on cumulative spectra of a large number of TGFs (e.g. [1]), which smooth out individual variability. The spectral analysis of individual TGFs has been carried out up to now for Fermi TGFs only, showing spectral diversity [2]. Crucial key factors for individual TGF spectral analysis are a large number of counts, an energy range extended to several tens of MeV, a good energy calibration as well as knowledge and control of any instrumental effects affecting the measurements.We strive to put stricter constraints on the production altitude and beaming geometry, by comparing Monte Carlo simulations to energy spectra from single ASIM TGFs. We will present the dataset and method, including the correction for instrumental effects, and preliminary results on individual TGFs.Thanks to ASIM’s large effective area and low orbital altitude, single TGFs detected by ASIM have much more count statistics than observations from other spacecrafts capable of detecting TGFs. ASIM has detected over 550 TGFs up to date (January 2020), and ~115 have more than 100 counts. This allows for a large sample for individual spectral analysis.References:Dwyer, J. R., and D. M. Smith (2005), A comparison between Monte Carlo simulations of runaway breakdown and terrestrial gamma-ray flash observations, Geophys. Res. Lett., 32, L22804, doi:10.1029/2005GL023848. Mailyan et al. (2016), The spectroscopy of individual terrestrial gamma-ray flashes: Constraining the source properties, J. Geophys. Res. Space Physics, 121, 11,346–11,363, doi:10.1002/2016JA022702.

Terrestrial Gamma-ray Flashes (TGFs) are short bursts of gamma radiation originating from thunderclouds; they propagate upwards and are then detected by satellites such as AGILE, Fermi and ASIM. ASIM is the first mission specifically designed for the study of thunderstorm-related phenomena (Neubert et al., 2019); being placed on the ISS, it can for the first time detect TGF events up to more than 51 degrees in latitude.Among the previous missions, RHESSI was the one reaching the highest latitude: 38 degrees. We then consider “high-latitude” for ASIM the band between 35 and 51 degrees of latitude. 9 events have already been observed in this band, inside four distinct geographical regions. At such latitudes, TGFs are expected to experience greater absorption in the troposphere, which makes them more difficult to detect. Moreover, we expect an intrinsically lower production rate due to the lower lightning activity (Smith et al., 2010, Williams et al., 2006).In this work we present the characteristics of those events, in the context of the global ASIM sample collected so far. We also examine whether the observed number of events is statistically compatible with the atmospheric absorption, taking into account the local flash activity and ASIM’s exposure at high latitude.

In 2018, the Atmospheric Space Interactions Monitor (ASIM) was launched and mounted onboard the Columbus module of the International Space Station (ISS). Using data from the Modular X- and Gamma-Ray Sensor (MXGS) and the Modular Multispectral Imaging Array (MMIA), we investigate the time sequence of the TGFs detected by MXGS and the optical pulses detected by the MMIA. The optical pulses are observed in the 337 nm and 777.4 nm, and the X- and gamma-rays are detected by the High Energy Detector of MXGS, which is sensitive to energies from 300 keV to more than 30 MeV. We will also look into the TGF duration and any correlation with the time between the TGFs and the main optical signals. The data used is from June 2018 (shortly after mounting on the Columbus module) until the end of March 2019, when the relative timing uncertainty between the two instruments was +/- 80 us. The data after this is presented in Skeie et al.

The Atmosphere Space Interaction Monitor (ASIM) mission onboard the International Space Station is the first mission specifically dedicated to the observation of Terrestrial Gamma-ray Flashes (TGF) and Transient Luminous Events (TLE). ASIM, together with the Fermi and AGILE satellites, are the only three currently operating missions capable to detect TGFs from space. Depending on orbital parameters, pairs of these missions periodically get closer than few hundreds kilometers, observing the same region on the Earth surface for up to several tens of seconds. This offers the unique chance to observe the same TGF from two different viewing angles. Such observations allow to probe the TGF production geometry and possibly put constraints on production models and electric field geometry at the source.Here we present four TGFs detected by ASIM and simultaneously detected by Fermi (three events) or AGILE (one event) in the period June 2018 - November 2019. We present location data, light curves, and possible constraints to emission geometry based on coupled observations and Monte Carlo simulations.

Using the Modular X- and Gamma-ray Sensor (MXGS) and the Modular Multi-spectral Imaging Array (MMIA) of the Atmosphere-Space Interactions Monitor (ASIM), we investigate the time sequence of the Terrestrial gamma-ray flashes and the optical emissions from the associated lighting. A common observation in the ASIM data is that the TGFs are observed before or during a weak increase in the optical signals in 337 nm and 777.4 nm, and prior to- or at the onset of the main optical pulse. Using data from the MXGS and MMIA instruments for the period from April 2019, we assess the time sequence and the relationship between the observed TGF duration and the time between the onset of the TGF and the onset of the main optical pulse, with a relative timeing uncertainty of +/- 5 µs. The data prior to April 2019 is presented in Bjørge-Engeland et al.

We report a 511‐keV photon flux enhancement that was observed inside a thundercloud and is a result of positron annihilation. The observation was made with the In‐flight Lightning Damage Assessment System (ILDAS) on board of an A340 test aircraft. The aircraft was intentionally flying through a thunderstorm at 12‐km altitude over Northern Australia in January 2016. Two gamma ray detectors showed a significant count rate increase synchronously with fast electromagnetic field variations registered by an on‐board antenna. A sequence of 10 gamma ray enhancements was detected, each lasted for about 1 s. Their spectrum mainly consists of 511‐keV photons and their Compton component. The local electric activity during the emission was identified as a series of static discharges of the aircraft. A full‐scale Geant4 model of the aircraft was created to estimate the emission area. Monte Carlo simulation indicated that the positrons annihilated in direct vicinity or in the aircraft body., Key Points A sequence of 10 X‐ray pulses was observed from an aircraft inside thundercloud at 12‐km altitudeThe pulses contain strong enhancement of the positron annihilation line (511 keV)Each pulse lasts for 1 s and is accompanied by a static discharge from the aircraft