Preprints
https://doi.org/10.5194/angeo-2020-95
https://doi.org/10.5194/angeo-2020-95

  07 Jan 2021

07 Jan 2021

Review status: a revised version of this preprint is currently under review for the journal ANGEO.

Fine Scale Dynamics of Fragmented Aurora-Like Emission

Daniel K. Whiter1, Hanna Dahlgren2, Betty S. Lanchester1, Joshua Dreyer3,4, Noora Partamies5,6, Nickolay Ivchenko7, Marco Zaccaria Di Fraia8, Rosie Oliver8, Amanda Serpell-Stevens8, Tiffany Shaw-Diaz8, and Thomas Braunersreuther8 Daniel K. Whiter et al.
  • 1Physics & Astronomy, University of Southampton, United Kingdom
  • 2Swedish Defence Research Agency (FOI), Stockholm, Sweden
  • 3Swedish Institute of Space Physics (IRF), Uppsala, Sweden
  • 4Department of Physics & Astronomy, Uppsala University, Sweden
  • 5University Centre in Svalbard (UNIS), Longyearbyen, Norway
  • 6Birkeland Centre for Space Science, Norway
  • 7Royal Institute of Technology (KTH), Stockholm, Sweden
  • 8Citizen scientist

Abstract. Fragmented Aurora-like Emissions (FAEs) are small (few km) optical structures which have been observed close to the poleward boundary of the aurora from the high-latitude location of Svalbard (magnetic latitude 75.3 ° N). The FAEs are only visible in certain emissions and their shape has no magnetic-field aligned component, suggesting that they are not caused by energetic particle precipitation and are therefore not aurora in the normal sense of the word. The FAEs sometimes form wave-like structures parallel to an auroral arc, with regular spacing between each FAE. They drift at a constant speed and exhibit internal dynamics moving at a faster speed than the envelope structure. The formation mechanism of FAEs is currently unknown.

We present an analysis of high-resolution optical observations of FAEs made during two separate events. Based on their appearance and dynamics we make the assumption that the FAEs are a signature of a dispersive wave in the lower E-region ionosphere, co-located with enhanced electron and ion temperatures detected by incoherent scatter radar. Their drift speed (group speed) is found to be 580–700 m s−1 and the speed of their internal dynamics (phase speed) is found to be 2200–2500 m s−1, both for an assumed altitude of 100 km. The speeds are similar for both events which are observed during different auroral conditions. We consider two possible waves which could produce the FAEs, electrostatic ion cyclotron waves and Farley-Buneman waves, and find that the observations could be consistent with either wave under certain assumptions. In the case of EIC waves the FAEs must be located at an altitude above about 140 km, and our measured speeds scaled accordingly. In the case of Farley-Buneman waves a very strong electric field of about 365 mV m−1 is required to produce the observed speeds of the FAEs; such a strong electric field may be a requirement for FAEs to occur.

Daniel K. Whiter et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on angeo-2020-95', Michael Kosch, 29 Apr 2021
    • AC1: 'Reply on RC1', Daniel Whiter, 19 Aug 2021
  • RC2: 'Comment on angeo-2020-95', Anonymous Referee #2, 08 Jun 2021
    • AC2: 'Reply on RC2', Daniel Whiter, 19 Aug 2021

Daniel K. Whiter et al.

Daniel K. Whiter et al.

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Short summary
This paper presents analysis of high-resolution optical and radar observations of a phenomenon called Fragments of Aurora-like Emission (FAEs), observed close to aurora in the high Arctic. The observations suggest that FAEs are not caused by high energy electrons or protons entering the atmosphere along Earth's magnetic field, and are therefore not aurora. The speeds of the FAEs and their internal dynamics were measured and used to evaluate theories for how the FAEs are produced.