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We compared the modeled energy spectral density of very low frequency (VLF) radio emissions from terrestrial gamma ray flashes (TGFs) with the energy spectral density of VLF radio sferics recorded by Duke VLF receiver simultaneously with those TGFs. In total, six events with world wide lightning location network (WWLLN) defined locations were analyzed to exhibit a good fit between the modeled and observed energy spectral densities. In VLF range the energy spectral density of the TGF source current moment is found to be dominated by the contribution of secondary low-energy electrons and independent of the relativistic electrons which play their role in low-frequency (LF) range. Additional spectral modulation by the multiplicity of TGF peaks was found and demonstrated a good fit for two TGFs whose VLF sferics consist of two overlapping pulses each. The number of seeding pulses in TGF defines the spectral shape in VLF range, which allows to retrieve this number from VLF sferics, assuming they were radiated by TGFs. For two events it was found that the number of seeding pulses is small, of the order of 10. For the rest of the events the lower boundary of the number of seeding pulses was found to be between 10 to 10.©2017. The Authors. ; This study was supported by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement 320839 and the Research Council of Norway under contracts 208028/F50 and 223252/F50 (CoE). The contributions of SAC were supported by NSF grant ATM-1565606. The work of FJPI was supported by the Spanish Ministry of Science and Innovation, MINECO under projects ESP2015-69909-C5-2-R and FIS2014-61774-EXP. F.J.P.I. acknowledges a PhD research contract, code BES-2014-069567. ; Peer Reviewed

The emerging field of high energy atmospheric physics (HEAP) includes terrestrial gamma-ray flashes, electron-positron beams and gamma-ray glows from thunderstorms. Similar emissions of high energy particles occur in pulsed high voltage discharges. Understanding these phenomena requires appropriate models for the interaction of electrons, positrons and photons of up to 40MeV energy with atmospheric air. In this paper, we benchmark the performance of the Monte Carlo codes Geant4, EGS5 and FLUKA developed in other fields of physics and of the custom-made codes GRRR and MC-PEPTITA against each other within the parameter regime relevant for high energy atmospheric physics. We focus on basic tests, namely on the evolution of monoenergetic and directed beams of electrons, positrons and photons with kinetic energies between 100keV and 40MeV through homogeneous air in the absence of electric and magnetic fields, using a low energy cutoff of 50keV. We discuss important differences between the results of the different codes and provide plausible explanations. We also test the computational performance of the codes. The Supplement contains all results, providing a first benchmark for present and future custom-made codes that are more flexible in including electrodynamic interactions. ; Alexander Broberg Skeltved is supported by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement 320839 and the Research Council of Norway under contracts 208028/F50, 216872/F50, and 223252/F50 (CoE). Alejandro Luque was supported by the European Research Council (ERC) under the European Union's H2020 programme/ERC grant agreement 681257 and by the Spanish Ministry of Economy and Competitiveness, MINECO under projects ESP2013-48032-C5-5-R and FIS2014-61774-EXP that include EU funding through the FEDER program. Gabriel Diniz is financial supported by the Brazilian agencies CAPES and CNPq. ; Peer Reviewed

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. ; Blue LUminous Events (BLUEs) are transient corona discharges occurring in thunderclouds and characterized by strong 337.0 nm light flashes with absent (or weak) 777.4 nm component. We present the first nighttime climatology of BLUEs as detected by the Modular Multispectral Imaging Array of the Atmosphere-Space Interaction Monitor showing their worldwide geographical and seasonal distribution. A total (land and ocean) of (Formula presented.) 11 BLUEs occur around the globe every second at local midnight and the average BLUE land/sea ratio is (Formula presented.) 7:4. The northwest region of Colombia shows an annual nighttime peak. Globally, BLUEs are maximized during the boreal summer-autumn, contrary to lightning which is maximed in the boreal summer. The geographical distribution of nighttime BLUEs shows three main regions in, by order of importance, the Americas, Europe/Africa and Asia/Australia. © 2021 The Authors. ; ASIM is a mission of ESA's SciSpace programme for scientific utilization of the ISS and non-ISS space exploration platforms and space environment analogues. ASIM and the ASIM Science Data Centre are funded by ESA and by National grants of Denmark, Norway and Spain. This work was supported by the Spanish Ministry of Science and Innovation under project PID2019-109269RB-C43 and the FEDER program. S. Soler acknowledges a PhD research contract through the project PID2019-109269RB-C43. F. J. Pérez-Invernón acknowledges the sponsorship provided by the Federal Ministry for Education and Research of Germany through the Alexander von Humboldt Foundation. A. Luque and D. Li were supported by the European Research Council (ERC) under European Union H2020 programme/ERC grant agreement 681257. S. Soler, F. J. Gordillo-Vázquez, A. Luque and D. Li acknowledge financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). ; Peer reviewed

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. ; On February 8, 2019, the Atmosphere-Space Interaction Monitor observed a terrestrial gamma-ray flash (TGF) and an Elve from a positive intracloud (+IC) lightning during the initial breakdown stage of a lightning flash north east of Puerto Rico. A second Elve produced by the return stroke (RS) of a negative cloud-to-ground (−CG) lightning was observed 456 ms later about 300 km south of the first one. Radio measurements show that a short (30 μs) and large (280 kA km) energetic in-cloud pulse (EIP) produced the electromagnetic (EM) wave for the first Elve while the RS of the −CG was the EM source for the second Elve. Assuming that the EIP and the RS were the sources of the 777 nm emissions, both the delay relative to the ultra-violet pulse and the shape and duration of the 777 nm emissions can be explained by scattering and absorption inside the clouds. The TGF produced by the +IC lightning had the same duration as the EIP (∼30 μs). Due to the ±80 μs timing uncertainty of the TGF, we can only state that TGF was produced just before or most likely simultaneously with the EIP. The large 777 nm pulse indicates that a large part of the EIP was produced by a current flowing in a hot channel, but it is likely that the TGF current also contributed significantly to the EIP. © 2021. The Authors. ; This study was supported by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 320839 and the Research Council of Norway under contracts 223252/F50 (CoE). This study has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skodowska-Curie grant agreement SAINT 722337. A.L. acknowledges support by the European Research Council (ERC) under the European Union H2020 program/ERC grant agreement 681257. This work was supported by the National Science Foundation Dynamic and Physical Meteorology program through grant AGS/1565606. The authors thank the International Space Science Institute, Bern, Switzerland, for providing financial support and meeting facilities in the frame of the International Team no. 471: Understanding the Properties of the Terrestrial Gamma-Ray Flash Population. ; With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709. ; Peer reviewed