Blar i Bergen Open Research Archive på forfatter "Østgaard, Nikolai"

Viser treff 41-60 av 68

    • The modular X- and gamma-ray sensor (MXGS) of the ASIM Payload on the International Space Station 

      Østgaard, Nikolai; Balling, Jan E.; Bjørnsen, Thomas Riis; Brauer, Peter; Budtz-Jørgensen, Carl; Bujwan, Waldemar; Carlson, Brant Edward; Christiansen, Freddy; Connell, Paul; Eyles, Chris; Fehlker, Dominik; Genov, Georgi; Grudzinski, Pawel; Kochkin, Pavlo; Kohfeldt, Anja; Kuvvetli, Irfan; Thomsen, Per Lundahl; Pedersen, Søren Møller; Navarro-Gonzalez, Javier; Neubert, Torsten; Njøten, Kåre; Orleanski, Piotr; Qureshi, Bilal Hasan; Cenkeramaddi, Linga Reddy; Reglero, Victor; Reina, Manuel; Rodrigo, Juan Manuel; Rostad, Maja Elise; Sabau, Maria D.; Kristensen, Steen Savstrup; Skogseide, Yngve; Solberg, Arne Olav; Stadsnes, Johan; Ullaland, Kjetil; Yang, Shiming (Peer reviewed; Journal article, 2019-02-18)
      The Modular X- and Gamma-ray Sensor (MXGS) is an imaging and spectral X- and Gamma-ray instrument mounted on the starboard side of the Columbus module on the International Space Station. Together with the Modular Multi-Spectral ...

    • Multi-Pulse Corona Discharges in Thunderclouds Observed in Optical and Radio Bands 

      Li, Dongshuai; Luque, Alejandro; Lehtinen, Nikolai Grigorievich; Gordillo-Vázquez, F.J.; Neubert, Torsten; Lu, Gaopeng; Chanrion, Olivier; Zhang, Hongbo; Østgaard, Nikolai; Reglero, Víctor (Journal article; Peer reviewed, 2022)
      How lightning initiates inside thunderclouds remains a major puzzle of atmospheric electricity. By monitoring optical emissions from thunderstorms, the Atmosphere-Space Interactions Monitor (ASIM) onboard the International ...

    • Multispectral Optical Diagnostics of Lightning from Space 

      Pérez-Invernón, Francisco J.; Gordillo-Vázquez, Francisco J.; Passas-Varo, María; Neubert, Torsten; Chanrion, Olivier; Reglero, Victor; Østgaard, Nikolai (Journal article; Peer reviewed, 2022)
      We present spectroscopic diagnostic methods that allow us to estimate the gas and the electron temperature in emerged lightning stroke channels (from thunderclouds) observed by the photometers and cameras of the Atmosphere ...

    • A new method reveals more TGFs in the RHESSI data 

      Gjesteland, Thomas; Østgaard, Nikolai; Collier, A. B.; Carlson, B. E.; Eyles, C.; Smith, D. M. (Peer reviewed; Journal article, 2012-03-07)

    • A new population of terrestrial gamma-ray flashes in the RHESSI data 

      Østgaard, Nikolai; Albrechtsen, Kjetil; Gjesteland, Thomas; Collier, Andrew B. (Peer reviewed; Journal article, 2015-12-23)
      Terrestrial gamma-ray flashes (TGFs) are the most energetic photon phenomenon occurring naturally on Earth. An outstanding question is as follows: Are these flashes just a rare exotic phenomenon or are they an intrinsic ...

    • North-south asymmetries in cold plasma density in the magnetotail lobes: Cluster observations 

      Haaland, Stein; Lybekk, Bjørn; Maes, Lukas; Laundal, Karl Magnus; Pedersen, Amund; Tenfjord, Paul; Ohma, Anders; Østgaard, Nikolai; Reistad, Jone Peter; Snekvik, Kristian (Peer reviewed; Journal article, 2017-01)
      In this paper, we present observations of cold (0–70 eV) plasma density in the magnetotail lobes. The observations and results are based on 16 years of Cluster observation of spacecraft potential measurements converted ...

    • Observation of intrinsically bright terrestrial gamma ray flashes from the Mediterranean basin 

      Gjesteland, Thomas; Østgaard, Nikolai; Laviola, Sante; Miglietta, M M; Arnone, Enrico; Marisaldi, Martino; Fuschino, F; Collier, Andrew B.; Fabro, F; Montanya, J (Peer reviewed; Journal article, 2015-12-14)
      We present three terrestrial gamma ray flashes (TGFs) observed over the Mediterranean basin by the Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) satellite. Since the occurrence of these events in the ...

    • Observations of Asymmetric Lobe Convection for Weak and Strong Tail Activity 

      Ohma, Anders; Østgaard, Nikolai; Reistad, Jone Peter; Tenfjord, Paul; Laundal, Karl Magnus; Moretto, Therese; Haaland, Stein; Krcelic, Patrik; Milan, Stephen Eric (Journal article; Peer reviewed, 2019)
      In this study we use high‐quality convection data from the Electron Drift Instrument on board Cluster to investigate how near‐Earth tail activity affects the average convection pattern in the magnetotail lobes when the ...

    • Observations of asymmetries in ionospheric return flow during different levels of geomagnetic activity 

      Reistad, Jone Peter; Østgaard, Nikolai; Laundal, Karl Magnus; Ohma, Anders; Snekvik, Kristian; Tenfjord, Paul; Grocott, Adrian; Oksavik, Kjellmar; Milan, Steve; Haaland, Stein (Peer reviewed; Journal article, 2018-06)
      It is known that the magnetic field of the Earth's closed magnetosphere can be highly displaced from the quiet‐day configuration when interacting with the interplanetary magnetic field (IMF), an asymmetry largely controlled ...

    • Observations of Blue Corona Discharges in Thunderclouds 

      Husbjerg, Lasse Skaaning; Neubert, Torsten; Chanrion, Olivier; Dimitriadou, Krystallia; Li, Dongshuai; Stendel, Martin; Kaas, Eigil; Østgaard, Nikolai; Reglero, Victor (Journal article; Peer reviewed, 2022)
      Blue electric streamer discharges in the upper reaches of thunderclouds are observed as flashes of 337.0 nm (blue) with faint or no emissions of 777.4 nm (red). Analyzing 3 years of measurements by the Atmosphere-Space ...

    • On the High‐Energy Spectral Component and Fine Time Structure of Terrestrial Gamma Ray Flashes 

      Marisaldi, Martino; Galli, M.; Labanti, C.; Østgaard, Nikolai; Sarria, David; Cummer, S. A.; Lyu, F.; Lindanger, Anders; Campana, R.; Ursi, A.; Tavana, M; Fuschino, F.; Argan, A.; Trois, A.; Pittori, C.; Verrecchia, F (Journal article; Peer reviewed, 2019)
      Terrestrial gamma ray flashes (TGFs) are very short bursts of gamma radiation associated to thunderstorm activity and are the manifestation of the highest‐energy natural particle acceleration phenomena occurring on Earth. ...

    • On the timing between terrestrial gamma ray flashes, radio atmospherics, and optical lightning emission 

      Gjesteland, Thomas; Østgaard, Nikolai; Bitzer, Phillip; Christian, Hugh J. (Peer reviewed; Journal article, 2017)
      On 25 October 2012 the Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) and the Tropical Rainfall Measuring Mission (TRMM) satellites passed over a thunderstorm on the coast of Sri Lanka. RHESSI observed a ...

    • Optical emissions associated with narrow bipolar events from thunderstorm clouds penetrating into the stratosphere 

      Liu, Feifan; Lu, Gaopeng; Neubert, Torsten; Lei, Jiuhou; Chanrion, Olivier; Østgaard, Nikolai; Li, Dongshuai; Luque, Alejandro; Gordillo-Vázquez, Francisco J.; Reglero, Victor; Lyu, Weitao; Zhu, Baoyou (Journal article; Peer reviewed, 2021)
      Narrow bipolar events (NBEs) are signatures in radio signals from thunderstorms observed by ground-based receivers. NBEs may occur at the onset of lightning, but the discharge process is not well understood. Here, we present ...

    • Overview of solar wind - magnetosphere - ionosphere - atmosphere coupling and the generation of magnetospheric currents 

      Milan, Stephen Eric; Clausen, Lasse Boy Novock; Coxon, John Charles; Carter, Jenny A.; Walach, Maria Theresia; Laundal, Karl Magnus; Østgaard, Nikolai; Tenfjord, Paul Arne Riksheim; Reistad, Jone Peter; Snekvik, Kristian; Korth, Haje; Anderson, Brian J. (Peer reviewed; Journal article, 2017-03)
      We review the morphology and dynamics of the electrical current systems of the terrestrial magnetosphere and ionosphere. Observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) ...

    • Production altitude and time delays of the terrestrial gamma flashes: Revisiting the Burst and Transient Source Experiment spectra 

      Østgaard, Nikolai; Gjesteland, Thomas; Stadsnes, J.; Connell, P. H.; Carlson, B. E. (Peer reviewed; Journal article, 2008-02-19)

    • Production of Terrestrial Gamma-Ray Flashes During the Early Stages of Lightning Flashes 

      Lindanger, Anders; Skeie, Chris Alexander Kallevik; Marisaldi, Martino; Bjørge-Engeland, Ingrid; Østgaard, Nikolai; Mezentsev, Andrey; Sarria, David Alexandre Stephan; Lehtinen, Nikolai Grigorievich; Reglero, Victor; Chanrion, Olivier; Neubert, Torsten (Journal article, 2022)
      Terrestrial Gamma-ray Flashes (TGFs) are short emissions of high energy photons associated with thunderstorms. It has been known since the discovery of TGFs that they are associated with lightning, and several case studies ...

    • Quantifying the Lobe Reconnection Rate During Dominant IMF By Periods and Different Dipole Tilt Orientations 

      Reistad, Jone Peter; Laundal, Karl Magnus; Østgaard, Nikolai; Ohma, Anders; Burrell, Angeline G.; Hatch, Spencer Mark; Håland, Stein Egil; Thomas, Evan G. (Journal article; Peer reviewed, 2021)
      Lobe reconnection is usually thought to play an important role in geospace dynamics only when the Interplanetary Magnetic Field (IMF) is mainly northward. This is because the most common and unambiguous signature of lobe ...

    • A Rapid Gamma-Ray Glow Flux Reduction Observed From 20 km Altitude 

      Kochkin, Pavlo; Sarria, David Alexandre Stephan; Lehtinen, Nikolai Grigorievich; Mezentsev, Andrey; Yang, Shiming; Genov, Georgi; Ullaland, Kjetil; Marisaldi, Martino; Østgaard, Nikolai; Christian, Hugh J.; Grove, J.E.; Quick, M.; Al-Nussirat, S.; Wulf, E (Journal article; Peer reviewed, 2021)
      Two gamma-ray glows were observed by a high-altitude NASA ER-2 aircraft flying at 20 km altitude over a thunderstorm in Colorado, USA. The flux of the first glow rapidly intensified and then abruptly decreased within a few ...

    • Separation and quantification of ionospheric convection sources: 1. A new technique 

      Reistad, Jone Peter; Laundal, Karl Magnus; Østgaard, Nikolai; Ohma, Anders; Haaland, Stein; Oksavik, Kjellmar; Milan, Stephen Eric (Peer reviewed; Journal article, 2019-07-04)
      This paper describes a novel technique that allows separation and quantification of different sources of convection in the high‐latitude ionosphere. To represent the ionospheric convection electric field, we use the Spherical ...

    • Separation and quantification of ionospheric convection sources: 2. The dipole tilt angle influence on reverse convection cells during northward IMF 

      Reistad, Jone Peter; Laundal, Karl Magnus; Østgaard, Nikolai; Ohma, Anders; Thomas, Evan G.; Haaland, Stein; Oksavik, Kjellmar; Milan, Stephen Eric (Peer reviewed; Journal article, 2019-07-04)
      This paper investigates the influence of Earth's dipole tilt angle on the reverse convection cells (sometimes referred to as lobe cells) in the Northern Hemisphere ionosphere during northward IMF, which we relate to ...