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Characteristics of fragmented aurora-like emissions (FAEs) observed on Svalbard

Characteristics of fragmented aurora-like emissions (FAEs) observed on Svalbard
Characteristics of fragmented aurora-like emissions (FAEs) observed on Svalbard
This study analyses the observations of a new type of small-scale aurora-like feature, which is further referred to as fragmented aurora-like emission(s) (FAEs). An all-sky camera captured these FAEs on three separate occasions in 2015 and 2017 at the Kjell Henriksen Observatory near the arctic town of Longyearbyen, Svalbard, Norway. A total of 305 FAE candidates were identified. They seem to appear in two categories – randomly occurring individual FAEs and wave-like structures with regular spacing between FAEs alongside auroral arcs. FAEs show horizontal sizes typically below 20 km, a lack of field-aligned emission extent, and short lifetimes of less than a minute. Emissions were observed at the 557.7 nm line of atomic oxygen and at 673.0 nm (N2; first positive band system) but not at the 427.8 nm emission of
N
+
2

or the 777.4 nm line of atomic oxygen. This suggests an upper limit to the energy that can be produced by the generating mechanism. Their lack of field-aligned extent indicates a different generation mechanism than for aurorae, which are caused by particle precipitation. Instead, these FAEs could be the result of excitation by thermal ionospheric electrons. FAE observations are seemingly accompanied by elevated electron temperatures between 110–120 km and increased ion temperatures at F-region altitudes. One possible explanation for this is Farley–Buneman instabilities of strong local currents. In the present study, we provide an overview of the observations and discuss their characteristics and potential generation mechanisms.
0992-7689
Dreyer, Joshua
1ad724c1-0066-4bf7-82c6-6a98172e0e79
Partamies, Noora
7219021b-a268-41eb-8e75-80550b7cf78f
Whiter, Daniel
9a30d7b6-ea41-44fb-bd52-3ff1964eca5c
Ellingsen, Pål
9623c5c0-7d56-495f-a320-88e3bfc3ae39
Baddeley, Lisa
4017b1a4-983b-4b1c-b6e0-af97ff0d8996
Buchert, Stephan
51579bb9-313e-476f-b64c-d008cb03d521
Dreyer, Joshua
1ad724c1-0066-4bf7-82c6-6a98172e0e79
Partamies, Noora
7219021b-a268-41eb-8e75-80550b7cf78f
Whiter, Daniel
9a30d7b6-ea41-44fb-bd52-3ff1964eca5c
Ellingsen, Pål
9623c5c0-7d56-495f-a320-88e3bfc3ae39
Baddeley, Lisa
4017b1a4-983b-4b1c-b6e0-af97ff0d8996
Buchert, Stephan
51579bb9-313e-476f-b64c-d008cb03d521

Dreyer, Joshua, Partamies, Noora, Whiter, Daniel, Ellingsen, Pål, Baddeley, Lisa and Buchert, Stephan (2021) Characteristics of fragmented aurora-like emissions (FAEs) observed on Svalbard. Annales Geophysicae, 39 (2). (doi:10.5194/angeo-39-277-2021).

Record type: Article

Abstract

This study analyses the observations of a new type of small-scale aurora-like feature, which is further referred to as fragmented aurora-like emission(s) (FAEs). An all-sky camera captured these FAEs on three separate occasions in 2015 and 2017 at the Kjell Henriksen Observatory near the arctic town of Longyearbyen, Svalbard, Norway. A total of 305 FAE candidates were identified. They seem to appear in two categories – randomly occurring individual FAEs and wave-like structures with regular spacing between FAEs alongside auroral arcs. FAEs show horizontal sizes typically below 20 km, a lack of field-aligned emission extent, and short lifetimes of less than a minute. Emissions were observed at the 557.7 nm line of atomic oxygen and at 673.0 nm (N2; first positive band system) but not at the 427.8 nm emission of
N
+
2

or the 777.4 nm line of atomic oxygen. This suggests an upper limit to the energy that can be produced by the generating mechanism. Their lack of field-aligned extent indicates a different generation mechanism than for aurorae, which are caused by particle precipitation. Instead, these FAEs could be the result of excitation by thermal ionospheric electrons. FAE observations are seemingly accompanied by elevated electron temperatures between 110–120 km and increased ion temperatures at F-region altitudes. One possible explanation for this is Farley–Buneman instabilities of strong local currents. In the present study, we provide an overview of the observations and discuss their characteristics and potential generation mechanisms.

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Accepted/In Press date: 20 January 2021
Published date: 4 March 2021

Identifiers

Local EPrints ID: 447557
URI: http://eprints.soton.ac.uk/id/eprint/447557
ISSN: 0992-7689
PURE UUID: a309628a-4c14-45a6-858c-32f977a4498c
ORCID for Daniel Whiter: ORCID iD orcid.org/0000-0001-7130-232X

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Date deposited: 16 Mar 2021 17:31
Last modified: 17 Mar 2021 02:41

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Contributors

Author: Joshua Dreyer
Author: Noora Partamies
Author: Daniel Whiter ORCID iD
Author: Pål Ellingsen
Author: Lisa Baddeley
Author: Stephan Buchert

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