• A-CHAIM: Near-Real-Time Data Assimilation of the High Latitude Ionosphere With a Particle Filter 

      Reid, Ben; Themens, David R.; McCaffrey, A; Jayachandran, P.T.; Johnsen, Magnar Gullikstad; Ulich, Thomas (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-02-28)
      The Assimilative Canadian High Arctic Ionospheric Model (A-CHAIM) is an operational ionospheric data assimilation model that provides a 3D representation of the high latitude ionosphere in Near-Real-Time (NRT). A-CHAIM uses low-latency observations of slant Total Electron Content (sTEC) from ground-based Global Navigation Satellite System (GNSS) receivers, ionosondes, and vertical TEC from ...
    • At the source of the polarisation of auroral emissions: experiments and modeling 

      Bosse, Léo; Lilensten, Jean; Gillet, Nicolas; Brogniez, Colette; Pujol, Olivier; Rochat, Sylvain; Delboulbé, Alain; Curaba, Stephane; Johnsen, Magnar Gullikstad (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-04-01)
      A polarised radiative transfer model (POMEROL) has been developed to compute the polarisation measured by a virtual instrument in a given nocturnal environment. This single-scattering model recreates real-world conditions (among them atmospheric and aerosol profiles, light sources with complex geometries at the ground and in the sky, terrain obstructions). It has been successfully tested at mid-latitudes ...
    • The auroral red line polarisation: modelling and measurements 

      Lilensten, J.; Bommier, V.; Barthelemy, M; Lamy, Herve; Bernard, D; Moen, Jøran Idar; Johnsen, Magnar Gullikstad; Løvhaug, Unni Pia; Pitout, Frederic (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-12)
      In this work, we model the polarisation of the auroral red line using the electron impact theory developed by Bommier et al. (2011). This theory enables the computation of the distribution of the Degree of Linear Polarisation (DoLP) as a function of height if the flux of precipitated electrons is provided as input. An electron transport code is used to infer the stationary electron flux at each ...
    • An automated auroral detection system using deep learning: real-time operation in Tromsø, Norway 

      Nanjo, Sota; Nozawa, Satonori; Yamamoto, Masaki; Kawabata, Tetsuya; Johnsen, Magnar Gullikstad; Tsuda, Takuo T.; Hosokawa, Keisuke (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-31)
      The activity of citizen scientists who capture images of aurora borealis using digital cameras has recently been contributing to research regarding space physics by professional scientists. Auroral images captured using digital cameras not only fascinate us, but may also provide information about the energy of precipitating auroral electrons from space; this ability makes the use of digital cameras ...
    • Challenges and Strategic Research Plans for Earth and Heliosphere: Research Infrastructures, Projects and Initiatives 

      Mann, Ingrid; Kauristie, Kirsti; Bamford, Ruth; McCrea, Ian; Moen, Jøran Idar; Oksavik, Kjellmar; Yamauchi, Masanori; Johnsen, Magnar Gullikstad; Turunen, Esa (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-24)
      We describe existing research infrastructures relevant for space weather and open issues of space weather research including the need for sustainable observation networks and for high-quality data products as basis for model development. The local relevance in Europe for studies of the ionosphere at high latitude is described. We propose as possible a way forward to sustain space weather research ...
    • The Dayside Open/Closed Field line Boundary -Ground-based optical determination and examination 

      Johnsen, Magnar Gullikstad (Doctoral thesis; Doktorgradsavhandling, 2011-12-20)
      The Open/Closed eld line Boundary (OCB) is the most important boundary in the magnetospheric system. On the dayside, the equatorward edge of the 6300 Å[OI] cusp aurora can be used as a proxy for the OCB. This work, which is a dissertation for the degree of philosophiæ Doctor consists of three scienti c papers focusing on the latitude of the optical cusp OCB and one paper focusing on polar cap patch ...
    • Determining the boundaries of the auroral oval from CHAMP field-aligned current signatures - Part 1 

      Xiong, Chao; Lühr, Hermann; Wang, Hui; Johnsen, Magnar Gullikstad (Journal article; Tidsskriftartikkel; Peer reviewed, 2014)
    • Effects of substorm electrojet on declination along concurrent geomagnetic latitudes in the northern auroral zone 

      Edvardsen, Inge; Johnsen, Magnar Gullikstad; Løvhaug, Unni Pia (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-09-02)
      The geomagnetic field often experiences large fluctuations, especially at high latitudes in the auroral zones. We have found, using simulations, that there are significant differences in the substorm signature, in certain coordinate systems, as a function of longitude. This is confirmed by the analysis of real, measured data from comparable locations. Large geomagnetic fluctuations pose ...
    • EISCAT Observation of Wave‐Like Fluctuations in Vertical Velocity of Polar Mesospheric Summer Echoes Associated With a Geomagnetic Disturbance 

      Lee, Young-Sook; Kim, Young Ha; Kim, Kyung-Chan; Kwak, Young-Sil; Sergiengko, Timothy; Kirkwood, Sheila; Johnsen, Magnar Gullikstad (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06-04)
      By analyzing a data set from the European Incoherent SCATter (EISCAT) Very High Frequency (VHF) radar at Tromsø, we find that both radar reflectivity and upward ion velocity in a polar mesospheric summer echo (PMSE) layer simultaneously increased at the commencement of a local geomagnetic disturbance, which occurred at midnight on 9 July 2013. The onset of the upward velocity was followed by periodic ...
    • Electric and magnetic senses in marine animals, and potential behavioral effects of electromagnetic surveys 

      Nyqvist, Daniel; Durif, Caroline; Johnsen, Magnar Gullikstad; de Jong, Karen; Forland, Tonje Nesse; Sivle, Lise Doksæter (Journal article; Tidsskriftartikkel, 2020-01-24)
      Electromagnetic surveys generate electromagnetic fields to map petroleum deposits under the seabed with unknown consequences for marine animals. The electric and magnetic fields induced by electromagnetic surveys can be detected by many marine animals, and the generated fields may potentially affect the behavior of perceptive animals. Animals using magnetic cues for migration or local orientation, ...
    • Geomagnetic induced currents in long subsea power cables 

      Solheim, Kristian Thinn; Johnsen, Magnar Gullikstad (Research report; Forskningsrapport, 2022-09-16)
      This report focuses on geomagnetically induced currents (GIC) that can be induced in long subsea power cables. Literature indicates that the water depth itself, in which the cable will be laid, will not contribute to an attenuation of the geoelectric field for those water depths relevant for the Krafla power cable. However, the presence of a coast will introduce a strong enhancement. Even minor ...
    • Geomagnetically induced currents in a Norwegian transformer station 

      Solheim, Kristian Thinn; Mo, Olve; Johnsen, Magnar Gullikstad (Research report; Forskningsrapport, 2022-05-11)
      This report considers measurements of geomagnetically induced current (GIC) and comparison to recorded variations in the geomagnetic field (dB/dt). The GIC-sensors were installed in the neutral point of a 420 kV transformer located in Mid-Norway in 2019. The magnetometers (for dB/dt) are also located in Mid-Norway, but at another location. Recordings up to December 2021 are presented in this report. ...
    • GMAG: An open-source python package for ground-based magnetometers 

      Murphy, Kyle R.; Rae, I. Jonathan; Halford, Alexa J.; Engebretson, Mark; Russell, Christopher T.; Matzka, Jürgen; Johnsen, Magnar Gullikstad; Milling, David K.; Mann, Ian R.; Kale, Andy; Xu, Zhonghua; Connors, Martin; Angelopoulos, Vassilis; Chi, Peter; Tanskanen, Eija Irene (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-04)
      Magnetometers are a key component of heliophysics research providing valuable insight into the dynamics of electromagnetic field regimes and their coupling throughout the solar system. On satellites, magnetometers provide detailed observations of the extension of the solar magnetic field into interplanetary space and of planetary environments. At Earth, magnetometers are deployed on the ground in ...
    • High-latitude crochet: Solar-flare-induced magnetic disturbance independent from low-latitude crochet 

      Yamauchi, Masatoshi; Johnsen, Magnar Gullikstad; Enell, Carl-Fredrik; Tjulin, Anders; Willer, Anna; Sormakov, Dmitry A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-11-03)
      A solar-flare-induced, high-latitude (peak at 70–75<sup>∘</sup> geographic latitude – GGlat) ionospheric current system was studied. Right after the X9.3 flare on 6 September 2017, magnetic stations at 68–77<sup>∘</sup> GGlat near local noon detected northward geomagnetic deviations (ΔB) for more than 3 h, with peak amplitudes of >200 nT without any accompanying substorm activities. From its location, ...
    • How Often Do Thermally Excited 630.0 nm Emissions Occur in the Polar Ionosphere? 

      Kwagala, Norah Kaggwa; Oksavik, Kjellmar; Lorentzen, Dag Arne; Johnsen, Magnar Gullikstad (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-17)
      This paper studies thermally excited emissions in the polar ionosphere derived from European Incoherent Scatter Svalbard radar measurements from the years 2000–2015. The peak occurrence is found around magnetic noon, where the radar observations show cusp-like characteristics. The ionospheric, interplanetary magnetic field and solar wind conditions favor dayside magnetic reconnection as the dominant ...
    • Ionospheric Response Observed by EISCAT During the 6–8 September 2017 Space Weather Event: Overview 

      Yamauchi, M; Sergiengko, Timothy; Enell, Carl-Fredrik; Schillings, A.; Slapak, R.; Johnsen, Magnar Gullikstad; Tjulin, A.; Nilsson, H. (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-03)
      We present ionospheric plasma conditions observed by the EISCAT radars in Tromsø and on Svalbard, covering 68°–81° geomagnetic latitude, during 6–8 September 2017. This is a period when X2.2 and X9.3 X‐ray flares occurred, two interplanetary coronal mass ejections (ICMEs) arrived at the Earth accompanied by enhancements of MeV‐range energetic particle flux in both the solar wind (SEP event) and inner ...
    • Measurement of the polarisation in the auroral N2+ 427.8 nm band 

      Barthélemy, Mathieu; Lamy, Hervé; Vialatte, Anne; Johnsen, Magnar Gullikstad; Cessateur, G; Zaourar, N (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-16)
      In this paper, we provide for the first time polarisation measurements of the <i>N</i><sup>+</sup><sub>2</sub> band at 427.8 nm performed with Premier Cru, a dedicated spectropolarimeter to investigate the polarisation of auroral emission lines between 400 and 700 nm. Details about the instrument, the observing conditions and the data analysis procedure are provided. Results obtained during three ...
    • Multiple E-Region Radar Propagation Modes Measured by the VHF SIMONe Norway System During Active Ionospheric Conditions 

      Huyghebaert, Devin Ray; Clahsen, Matthias; Chau, Jorge L.; Renkwitz, Toralf; Latteck, Ralph; Johnsen, Magnar Gullikstad; Vierinen, Juha (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-10)
      Multiple propagation modes between different bistatic radar links were measured during the operations of a very high frequency (VHF) 32.55 MHz radar system in northern Norway. The Spread Spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) Norway system detected meteor trails, direct transmitter to receiver signal propagation, over-the-horizon signal propagation from the ...
    • Neurosensory and vascular symptoms and clinical findings in the hands of Arctic open-pit miners in Sweden and Norway–a descriptive study 

      Stjernbrandt, Albin; Johnsen, Magnar Gullikstad; Liljelind, Ingrid; Aminoff, Anna Louise; Wahlström, Jens; Höper, Anje Christina; Pettersson, Hans; Nilsson, Tohr (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-05)
      This cross-sectional study aimed to describe exposure to cold climate and hand-arm vibration (HAV) as well as neurosensory and vascular symptoms and clinical findings among open-pit Arctic miners. It was based on data from questionnaires and physical examinations, including 177 men and 75 women from two open-pit mines in Sweden and Norway (response rate 54%). Working outdoors or in an unheated ...
    • On the contribution of thermal excitation to the total 630.0 nm emissions in the northern cusp ionosphere 

      Kwagala, Norah Kaggwa; Oksavik, Kjellmar; Lorentzen, Dag Arne; Johnsen, Magnar Gullikstad (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-01-25)
      Direct impact excitation by precipitating electrons is believed to be the main source of 630.0 nm emissions in the cusp ionosphere. However, this paper investigates a different source, 630.0 emissions caused by thermally excited atomic oxygen O(1D) when high electron temperature prevail in the cusp. On 22 January 2012 and 14 January 2013, the European Incoherent Scatter Scientific Association (EISCAT) ...