Fine-scale dynamics of fragmented aurora-like emissions
Fine-scale dynamics of fragmented aurora-like emissions
Fragmented aurora-like emissions (FAEs) are small (few kilometres) 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, i.e. electrostatic ion cyclotron waves (EIC) 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.
975-989
Whiter, Daniel
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Sundberg, Hanna
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Lanchester, Betty
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Dreyer, Joshua
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Partamies, Noora
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Ivchenko, Nickolay
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Zaccaria Di Fraia, Marco
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Oliver, Rosie
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Serpell-Stevens, Amanda
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Shaw-Diaz, Tiffany
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Braunersreuther, Thomas
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25 November 2021
Whiter, Daniel
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Sundberg, Hanna
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Lanchester, Betty
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Dreyer, Joshua
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Partamies, Noora
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Ivchenko, Nickolay
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Zaccaria Di Fraia, Marco
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Oliver, Rosie
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Serpell-Stevens, Amanda
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Shaw-Diaz, Tiffany
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Braunersreuther, Thomas
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Whiter, Daniel, Sundberg, Hanna, Lanchester, Betty, Dreyer, Joshua, Partamies, Noora, Ivchenko, Nickolay, Zaccaria Di Fraia, Marco, Oliver, Rosie, Serpell-Stevens, Amanda, Shaw-Diaz, Tiffany and Braunersreuther, Thomas
(2021)
Fine-scale dynamics of fragmented aurora-like emissions.
Annales Geophysicae, 39 (6), .
(doi:10.5194/angeo-39-975-2021).
Abstract
Fragmented aurora-like emissions (FAEs) are small (few kilometres) 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, i.e. electrostatic ion cyclotron waves (EIC) 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.
Text
angeo-2020-95-manuscript-version4
- Accepted Manuscript
More information
Accepted/In Press date: 20 October 2021
Published date: 25 November 2021
Additional Information:
Funding Information:
Independent Research Fellowship (grant no. NE/S015167/1). Noora Partamies has partially been supported by the Norwegian Research Council (NRC; CoE grant no. 223252 and NRC grant no. 287427). ASK has been funded by STFC and NERC of the United Kingdom (grant nos. PP/C502614/1, NE/H024433/1, NE/N004051/1, and NE/S015167/1) and Vetenskapsrådet of Sweden. EISCAT is supported by the research councils of Norway, Sweden, Finland, Japan, China, and the United Kingdom. The development of Aurora Zoo was funded by NERC (grant no. NE/N004051/1).
Funding Information:
Acknowledgements. This publication uses data generated via the Zooniverse.org platform, development of which is funded by generous support, including a Global Impact Award from Google, and by a grant from the Alfred P. Sloan Foundation. We thank the Zooni-verse team, for enabling and supporting the Aurora Zoo project, and the Aurora Zoo team, for developing, operating, and maintaining Aurora Zoo. We thank the members of the campaign team that set up and ran the ASK instrument during the winters of 2013–2014 (Sam Tuttle, Olli-Pekka Jokiaho, and Henry Pindeo) and 2014– 2015 (Sam Tuttle and Nicola Schlatter).
Publisher Copyright:
© 2021 Daniel K. Whiter et al.
Identifiers
Local EPrints ID: 452171
URI: http://eprints.soton.ac.uk/id/eprint/452171
ISSN: 0992-7689
PURE UUID: 8d3fb621-6f8a-4450-9bf1-73dfffe1f7ba
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Date deposited: 26 Nov 2021 17:34
Last modified: 17 Mar 2024 03:14
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Author:
Hanna Sundberg
Author:
Betty Lanchester
Author:
Joshua Dreyer
Author:
Noora Partamies
Author:
Nickolay Ivchenko
Author:
Marco Zaccaria Di Fraia
Author:
Rosie Oliver
Author:
Amanda Serpell-Stevens
Author:
Tiffany Shaw-Diaz
Author:
Thomas Braunersreuther
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