• The 3rd AGILE Terrestrial Gamma Ray Flash Catalog. Part I: Association to Lightning Sferics 

      Lindanger, Anders; Marisaldi, Martino; Maiorana, Carolina; Sarria, David; Albrechtsen, Kjetil; Østgaard, Nikolai; Galli, M.; Ursi, Alessandro; Labanti, C.; Tavani, Marco; Pittori, C.; Verrecchia, F. (Journal article; Peer reviewed, 2020)
      We present a complete and systematic search for terrestrial gamma-ray flashes (TGFs), detected by AGILE, that are associated with radio sferics detected by the World Wide Lightning Location Network (WWLLN) in the period ...
    • The 3rd AGILE Terrestrial Gamma-ray Flashes Catalog. Part II: Optimized Selection Criteria and Characteristics of the New Sample 

      Maiorana, Carolina; Marisaldi, Martino; Lindanger, Anders; Østgaard, Nikolai; Ursi, Alessandro; Sarria, David; Galli, M.; Labanti, C.; Tavani, Marco; Pittori, C.; Verrecchia, F. (Journal article; Peer reviewed, 2020)
      We present in this work the third catalog of terrestrial gamma-ray flashes (TGFs) by the AGILE mission and the new search algorithm that was developed to produce it. We firstly introduce the new selection criteria, designed ...
    • An altitude and distance correction to the initial fluence distribution of TGFs 

      Nisi, Ragnhild Schrøder; Østgaard, Nikolai; Gjesteland, Thomas; Collier, Andrew B. (Peer reviewed; Journal article, 2014-10)
      The source fluence distribution of terrestrial gamma ray flashes (TGFs) has been extensively discussed in recent years, but few have considered how the TGF fluence distribution at the source, as estimated from satellite ...
    • Analysis of Blue Corona Discharges at the Top of Tropical Thunderstorm Clouds in Different Phases of Convection 

      Dimitriadou, Krystallia; Chanrion, Olivier; Neubert, Torsten; Protat, Alain; Louf, Valentin; Heumesser, Matthias; Husbjerg, Lasse; Köhn, Christoph; Østgaard, Nikolai; Reglero, Victor (Journal article; Peer reviewed, 2022)
      We report on observations of corona discharges at the uppermost region of clouds characterized by emissions in a blue band of nitrogen molecules at 337 nm, with little activity in the red band of lightning leaders at 777.4 ...
    • The ASIM mission on the international space station 

      Neubert, Torsten; Østgaard, Nikolai; Reglero, Victor; Blanc, Elisabeth; Chanrion, Olivier; Oxborrow, Carol Anne; Orr, Astrid; Tacconi, Matteo; Hartnack, Ole; Bhanderi, Dan D.V. (Peer reviewed; Journal article, 2019-03-12)
      The Atmosphere-Space Interactions Monitor (ASIM) is an instrument suite on the International Space Station (ISS) for measurements of lightning, Transient Luminous Events (TLEs) and Terrestrial Gamma-ray Flashes (TGFs). ...
    • The asymmetric geospace as displayed during the geomagnetic storm on 17 August 2001 

      Østgaard, Nikolai; Reistad, Jone Peter; Tenfjord, Paul; Laundal, Karl Magnus; Rexer, Theresa; Haaland, Stein; Snekvik, Kristian; Hesse, Michael; Milan, Stephen Eric; Ohma, Anders (Peer reviewed; Journal article, 2018-11-29)
      Previous studies have shown that conjugate auroral features are displaced in the two hemispheres when the interplanetary magnetic field (IMF) has a transverse (Y) component. It has also been shown that a BY component is ...
    • Birkeland current effects on high-latitude ground magnetic field perturbations 

      Laundal, Karl Magnus; Haaland, Stein; Lehtinen, Nikolai; Gjerløv, Jesper; Østgaard, Nikolai; Tenfjord, Paul; Reistad, Jone Peter; Snekvik, Kristian; Milan, Steve; Ohtani, Shin-ichi; Anderson, Brian J. (Peer reviewed; Journal article, 2015-09-18)
      Magnetic perturbations on ground at high latitudes are directly associated only with the divergence-free component of the height-integrated horizontal ionospheric current, J⊥,df. Here we show how J⊥,df can be expressed as ...
    • Blue Flashes as Counterparts to Narrow Bipolar Events: The Optical Signal of Shallow In-Cloud Discharges 

      Li, Dongshuai; Luque, Alejandro; Gordillo-Vázquez, F.J.; Liu, Feifan; Lu, Gaopeng; Neubert, Torsten; Chanrion, Olivier; Zhu, Baoyou; Østgaard, Nikolai; Reglero, Víctor (Journal article; Peer reviewed, 2021)
      Narrow Bipolar Events (NBEs) are powerful radio emissions from thunderstorms, which have been recently associated with blue optical flashes on cloud tops and attributed to extensive streamer electrical discharges named ...
    • Can magnetotail reconnection produce the auroral intensities observed in the conjugate ionosphere? 

      Østgaard, Nikolai; Snekvik, Kristian; Borg, Anette Lauen; Åsnes, Arne; Pedersen, Arne; Øieroset, Marit; Phan, Tai D.; Haaland, Stein (Peer reviewed; Journal article, 2009-06)
      [1] In a recent case study, Borg et al. (2007) reported that an inverted V structure, caused by a field-aligned potential drop of 30 kV producing very strong X-ray aurora, was found in connection with tail reconnection. ...
    • Characterization of Thunderstorm Cells Producing Observable Terrestrial Gamma-Ray Flashes 

      Husbjerg, Lasse Skaaning; Neubert, Torsten; Chanrion, Olivier; Marisaldi, Martino; Stendel, Martin; Kaas, Eigil; Østgaard, Nikolai; Reglero, Victor (Journal article; Peer reviewed, 2023)
      The meteorological conditions required for the production of Terrestrial Gamma-ray Flashes (TGFs) are not well understood. Particularly, the link between TGF production, meteorology, and weather severity is poorly characterized ...
    • Cluster observations of a field aligned current at the dawn flank of a bursty bulk flow 

      Snekvik, Kristian; Haaland, Stein; Østgaard, Nikolai; Hasegawa, H.; Nakamura, R.; Takada, T.; Juusola, L.; Amm, O.; Pitout, F.; Rème, H.; Klecker, B.; Lucek, E. A. (Peer reviewed; Journal article, 2007-06-29)
      This article describes observations of a bursty bulk flow (BBF) in the outer central plasma sheet. The observations are made with the Cluster satellites, located approximately 19RE downtail, close to the midnight sector ...
    • Confining the angular distribution of terrestrial gamma ray flash emission 

      Gjesteland, Thomas; Østgaard, Nikolai; Collier, A. B.; Carlson, B. E.; Cohen, M. B.; Lehtinen, N. G. (Peer reviewed; Journal article, 2011-11-11)
    • Constraining Spectral Models of a Terrestrial GammaRay Flash From a Terrestrial Electron Beam Observation by the Atmosphere-Space Interactions Monitor 

      Sarria, David Alexandre Stephan; Østgaard, Nikolai; Kochkin, Pavlo; Lehtinen, Nikolai Grigorievich; Mezentsev, Andrey; Marisaldi, Martino; Lindanger, Anders; Maiorana, Carolina; Carlson, Brant Edward; Neubert, Torsten; Reglero, Victor; Ullaland, Kjetil; Yang, Shiming; Genov, Georgi; Qureshi, Bilal Hasan; Budtz-Jørgensen, Carl; Kuvvetli, Irfan; Christiansen, Freddy; Chanrion, Olivier; Navarro-Gonzalez, Javier; Connel, P.; Eyles, Chris (Journal article; Peer reviewed, 2021)
      Terrestrial Gamma ray Flashes (TGFs) are short flashes of high energy photons, produced by thunderstorms. When interacting with the atmosphere, they produce relativistic electrons and positrons, and a part gets bounded to ...
    • Constraints on Recoil Leader Properties Estimated from X-ray Emissions in Aircraft-Triggered Discharges 

      Skeie, Chris Alexander Kallevik; Østgaard, Nikolai; Lehtinen, Nikolai; Sarria, David; Kochkin, Pavlo; de Boer, Boer; Bardet, M.; Allasia, C.; Flourens, F. (Journal article; Peer reviewed, 2020)
      During Airbus aircraft campaigns flying into thunderstorms in 2014–2016, X-rays were observed during two stages of aircraft-triggered lightning: nanosecond pulses of X-rays associated with negative leader steps and bursts ...
    • Constraints to do realistic modeling of the electric field ahead of the tip of a lightning leader 

      Skeltved, Alexander Broberg; Østgaard, Nikolai; Mezentsev, Andrey; Lehtinen, Nikolai; Carlson, Brant Edward (Peer reviewed; Journal article, 2017-08)
      Several computer models exist to explain the observation of terrestrial gamma‐ray flashes (TGFs). Some of these models estimate the electric field ahead of lightning leaders and its effects on electron acceleration and ...
    • Dayside and nightside magnetic field responses at 780 km altitude to dayside reconnection 

      Snekvik, Kristian; Østgaard, Nikolai; Tenfjord, Paul; Reistad, Jone Peter; Laundal, Karl Magnus; Milan, Stephen Eric; Haaland, Stein (Peer reviewed; Journal article, 2017-02)
      During southward interplanetary magnetic field, dayside reconnection will drive the Dungey cycle in the magnetosphere, which is manifested as a two‐cell convection pattern in the ionosphere. We address the response of the ...
    • Dynamic effects of restoring footpoint symmetry on closed magnetic field lines 

      Reistad, Jone Peter; Østgaard, Nikolai; Tenfjord, Paul; Laundal, Karl Magnus; Snekvik, Kristian; Haaland, Stein; Milan, Steve; Oksavik, Kjellmar; Frey, H. U.; Grokott, A. (Peer reviewed; Journal article, 2016-05-05)
      Here we present an event where simultaneous global imaging of the aurora from both hemispheres reveals a large longitudinal shift of the nightside aurora of about 3 h, being the largest relative shift reported on from ...
    • Effects of dead time losses on terrestrial gamma ray flash measurements with the Burst and Transient Source Experiment 

      Gjesteland, Thomas; Østgaard, Nikolai; Connell, P. H.; Stadsnes, J.; Fishman, G. J. (Peer reviewed; Journal article, 2010-05-05)
    • Enhanced detection of terrestrial gamma-ray flashes by AGILE 

      Marisaldi, Martino; Argan, A; Ursi, Alessandro; Gjesteland, Thomas; Fuschino, F; Labanti, C; Galli, M; Tavani, M; Pittori, C; Verrecchia, F; D´Amico, F.; Østgaard, Nikolai; Mereghetti, S; Campana, R; Cattaneo, PW; Bulgarelli, S; Colafrancesco, S; Dietrich, S; Longo, F; Gianotti, F.; Giommi, P; Rappoldi, A; Trifoglio, M; Trois, A (Peer reviewed; Journal article, 2015-11-06)
      At the end of March 2015 the onboard software configuration of the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite was modified in order to disable the veto signal of the anticoincidence shield for the minicalorimeter ...
    • Evolution of IMF By induced asymmetries during substorms: Superposed epoch analysis at geosynchronous orbit 

      Ohma, Anders; Laundal, Karl Magnus; Reistad, Jone Peter; Østgaard, Nikolai (Journal article; Peer reviewed, 2022)
      The By component of the magnetic field inside the magnetosphere is positively correlated with the By component of the Interplanetary Magnetic Field (IMF). This leads to asymmetries in aurora, plasma convection and electric ...