Javier Navarro-González

During ASIM operations from June 2018 until the end of 2019, 486 TGFs were observed. For this task, the ASDC (ASIM Science Data Center) dealt with numerous triggers from the instrument (5000 per week). The relocation of the instrument from EPF SDX to EPF SDN (Starboard Deck Nadir) of the Columbus ISS Module on January 10, 2022, demonstrated that the MXGS location capabilities could be used not only for TGF location but also for imaging GRB events, as its Field of View in the SDN port encompasses both Earth and space.It's worth noting that only a few of the ASIM triggers correspond to TGF events. There is a screening process employing a series of algorithms to detect and discard false positives (triggers that are not TGFs). Nevertheless, the ASIM archive retains all data from every trigger. Due to the extended operational time, there is currently a sufficiently large database that enables us to present the initial results here using novel machine learning methods, such as kernel methods or neural networks, for the automatic categorization of both present and future events.Furthermore, our interest goes beyond mere classification, as we are currently investigating whether various explainability methods applied to these techniques can assist in identifying the relevant features of the signal for such classification. The aim of this work is to provide a tool to quantify new physical processes that could be the cause of instrument triggers and to examine whether there is a connection with the Earth-Space global circuit.

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.

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.

We present nighttime worldwide distributions of key features of Blue LUminous Events (BLUEs) detected by the Modular Multispectral Imaging Array of the Atmosphere‐Space Interaction Monitor. Around 10% of all detected BLUEs exhibit an impulsive single pulse 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 −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 ∼4 km height) and have the largest number of streamers (up to ∼3 × 10⁹). Additionally, the analysis of BLUEs has turned out to be particularly complex due to the abundance of radiation belt particles (at high latitudes and in the South Atlantic Anomaly [SAA]) and cosmic rays all over the planet. True BLUEs can not be fully distinguished from radiation belt particles and cosmic rays unless other ground‐based measurements associated with the optically detected BLUEs are available. Thus, the search algorithm of BLUEs presented in Soler et al. (2021), https://doi.org/10.1029/2021gl094657 is now completed with a new additional step that, if used, can considerably smooth the SAA shadow but can also underestimate the number of BLUEs worldwide.

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

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

Magnetars are strongly magnetized, isolated neutron stars^1,2,3 with magnetic fields up to around 10¹⁵ gauss, luminosities of approximately 10³¹–10³⁶ ergs per second and rotation periods of about 0.3–12.0 s. Very energetic giant flares from galactic magnetars (peak luminosities of 10⁴⁴–10⁴⁷ ergs per second, lasting approximately 0.1 s) have been detected in hard X-rays and soft γ-rays⁴, and only one has been detected from outside our galaxy⁵. During such giant flares, quasi-periodic oscillations (QPOs) with low (less than 150 hertz) and high (greater than 500 hertz) frequencies have been observed^6,7,8,9, but their statistical significance has been questioned¹⁰. High-frequency QPOs have been seen only during the tail phase of the flare⁹. Here we report the observation of two broad QPOs at approximately 2,132 hertz and 4,250 hertz in the main peak of a giant γ-ray flare¹¹ in the direction of the NGC 253 galaxy^{12,13,14,15,16,17}, disappearing after 3.5 milliseconds. The flare was detected on 15 April 2020 by the Atmosphere–Space Interactions Monitor instrument^18,19 aboard the International Space Station, which was the only instrument that recorded the main burst phase (0.8–3.2 milliseconds) in the full energy range (50 × 10³ to 40 × 10⁶ electronvolts) without suffering from saturation effects such as deadtime and pile-up. Along with sudden spectral variations, these extremely high-frequency oscillations in the burst peak are a crucial component that will aid our understanding of magnetar giant flares.

Lightning is the major cause of the natural ignition of wildfires worldwide and produces the largest wildfires in some regions. Lightning strokes produce about 5 % of forest fires in the Mediterranean Basin and are one of the most important precursors of the largest forest fires during the summer. Lightning-ignited wildfires produce significant emissions of aerosols, black carbon, and trace gases, such as CO, SO₂, CH₄, and O₃, affecting air quality. Characterization of the meteorological and cloud conditions of lightning-ignited wildfires in the Mediterranean Basin can serve to improve fire forecasting models and to upgrade the implementation of fire emissions in atmospheric models. This study investigates the meteorological and cloud conditions of lightning-ignited wildfires (LIWs) and long continuing current (LCC) lightning flashes in the Iberian Peninsula and Greece. LCC lightning and lightning in dry thunderstorms with a low precipitation rate have been proposed to be the main precursors of the largest wildfires. We use lightning data provided by the World Wide Lightning Location Network (WWLLN), the Earth Networks Total Lightning Network (ENTLN), and the Lightning Imaging Sensor (LIS) on board the International Space Station (ISS), together with four databases of wildfires produced in Spain, Portugal, southern France, and Greece, respectively, in order to produce a climatology of LIWs and LCC lightning over the Mediterranean Basin. In addition, we use meteorological data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis data set and by the Spanish State Meteorological Agency (AEMET), together with the Cloud Top Height product (CTHP) derived from Meteosat Second Generation (MSG) satellites measurements to investigate the meteorological conditions of LIWs and LCC lightning. According to our results, LIWs and a significant amount of LCC lightning flashes tend to occur in dry thunderstorms with weak updrafts. Our results suggest that LIWs tend to occur in clouds with a high base and with a vertical content of moisture lower than the climatological value, as well as with a higher temperature and a lower precipitation rate. Meteorological conditions of LIWs from the Iberian Peninsula and Greece are in agreement, although some differences possibly caused by the highly variable topography in Greece and a more humid environment are observed. These results show the possibility of using the typical meteorological and cloud conditions of LCC lightning flashes as proxy to parameterize the ignition of wildfires in atmospheric or forecasting models.

Lightning is the major cause of natural ignition of wildfires worldwide and produces the largest wildfires in some regions. Lightning strokes produce about 5 % of forest fires in the Mediterranean basin and are one of the most important precursors of the largest forest fires during the summer. Lightning-ignited wildfires produce significant emissions of aerosols, black carbon and trace gases, such as CO, SO₂, CH₄ and O₃, affecting air quality. Characterization of the meteorological and cloud conditions of lightning-ignited wildfires in the Mediterranean basin can serve to improve fire forecasting models and to upgrade the implementation of fire emissions in atmospheric models. This study investigates the meteorological and cloud conditions of Lightning-Ignited Wildfires (LIW) and Long-Continuing-Current (LCC) lightning flashes in the Iberian Peninsula and Greece. LCC lightning and lightning in dry thunderstorms with low precipitation rate have been proposed to be the main precursors of the largest wildfires. We use lightning data provided by the World Wide Lightning Location Network (WWLLN), the Earth Network Total Lightning Network (ENTLN) and the Lightning Imaging Sensor (LIS) onboard the International Space Station (ISS) together with four databases of wildfires produced in Spain, Portugal, Southern France and Greece, respectively, in order to produce a climatology of LIW and LCC lightning over the Mediterranean basin. In addition, we use meteorological data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5-reanalysis data set and by the Spanish State Meteorological Agency (AEMET) together with the Cloud Top Height (CTH) product derived from Meteosat Second Generation (MSG) satellites measurements to investigate the meteorological conditions of LIW and LCC lightning. According to our results, LIW and a significant amount of LCC lightning flashes tend to occur in dry thunderstorms with weak updrafts. Our results suggest that lightning-ignited wildfires tend to occur in high-based clouds with a vertical content of moisture lower than the climatological value, as well as with a higher temperature and a lower precipitation rate. Meteorological conditions of LIW from the Iberian Peninsula and Greece are in agreement, although some differences possibly caused by highly variable topography in Greece and a more humid environment are observed. These results show the possibility of using the typical meteorological and cloud conditions of LCC lightning flashes as proxy to parameterize the ignition of wildfires in atmospheric or forecasting models.