Fine-scale dynamics of fragmented aurora-like emissions

<p>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 <span class="inline-formula"><sup>∘</sup&g...

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Autores principales:	D. K. Whiter, H. Sundberg, B. S. Lanchester, J. Dreyer, N. Partamies, N. Ivchenko, M. Z. Di Fraia, R. Oliver, A. Serpell-Stevens, T. Shaw-Diaz, T. Braunersreuther
Formato:	article
Lenguaje:	EN
Publicado:	Copernicus Publications 2021
Materias:	Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809
Acceso en línea:	https://doaj.org/article/98d6df1010964ae1985c3d009f994286
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spelling	oai:doaj.org-article:98d6df1010964ae1985c3d009f9942862021-11-25T10:49:31ZFine-scale dynamics of fragmented aurora-like emissions10.5194/angeo-39-975-20210992-76891432-0576https://doaj.org/article/98d6df1010964ae1985c3d009f9942862021-11-01T00:00:00Zhttps://angeo.copernicus.org/articles/39/975/2021/angeo-39-975-2021.pdfhttps://doaj.org/toc/0992-7689https://doaj.org/toc/1432-0576<p>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 <span class="inline-formula"><sup>∘</sup></span>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.</p> <p>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<span class="inline-formula"><sup>−1</sup></span>, and the speed of their internal dynamics (phase speed) is found to be 2200–2500 m s<span class="inline-formula"><sup>−1</sup></span>, 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<span class="inline-formula"><sup>−1</sup></span> is required to produce the observed speeds of the FAEs; such a strong electric field may be a requirement for FAEs to occur.</p>D. K. WhiterH. SundbergB. S. LanchesterJ. DreyerJ. DreyerN. PartamiesN. PartamiesN. IvchenkoM. Z. Di FraiaR. OliverA. Serpell-StevensT. Shaw-DiazT. BraunersreutherCopernicus PublicationsarticleScienceQPhysicsQC1-999Geophysics. Cosmic physicsQC801-809ENAnnales Geophysicae, Vol 39, Pp 975-989 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809
spellingShingle	Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 D. K. Whiter H. Sundberg B. S. Lanchester J. Dreyer J. Dreyer N. Partamies N. Partamies N. Ivchenko M. Z. Di Fraia R. Oliver A. Serpell-Stevens T. Shaw-Diaz T. Braunersreuther Fine-scale dynamics of fragmented aurora-like emissions
description	<p>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 <span class="inline-formula"><sup>∘</sup></span>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.</p> <p>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<span class="inline-formula"><sup>−1</sup></span>, and the speed of their internal dynamics (phase speed) is found to be 2200–2500 m s<span class="inline-formula"><sup>−1</sup></span>, 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<span class="inline-formula"><sup>−1</sup></span> is required to produce the observed speeds of the FAEs; such a strong electric field may be a requirement for FAEs to occur.</p>
format	article
author	D. K. Whiter H. Sundberg B. S. Lanchester J. Dreyer J. Dreyer N. Partamies N. Partamies N. Ivchenko M. Z. Di Fraia R. Oliver A. Serpell-Stevens T. Shaw-Diaz T. Braunersreuther
author_facet	D. K. Whiter H. Sundberg B. S. Lanchester J. Dreyer J. Dreyer N. Partamies N. Partamies N. Ivchenko M. Z. Di Fraia R. Oliver A. Serpell-Stevens T. Shaw-Diaz T. Braunersreuther
author_sort	D. K. Whiter
title	Fine-scale dynamics of fragmented aurora-like emissions
title_short	Fine-scale dynamics of fragmented aurora-like emissions
title_full	Fine-scale dynamics of fragmented aurora-like emissions
title_fullStr	Fine-scale dynamics of fragmented aurora-like emissions
title_full_unstemmed	Fine-scale dynamics of fragmented aurora-like emissions
title_sort	fine-scale dynamics of fragmented aurora-like emissions
publisher	Copernicus Publications
publishDate	2021
url	https://doaj.org/article/98d6df1010964ae1985c3d009f994286
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Fine-scale dynamics of fragmented aurora-like emissions

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