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Eastward-expanding auroral surges observed in the post-midnight sector during a multiple-onset substorm

Eastward-expanding auroral surges observed in the post-midnight sector during a multiple-onset substorm
Eastward-expanding auroral surges observed in the post-midnight sector during a multiple-onset substorm
We present three eastward-expanding auroral surge (EEAS) events that were observed intermittently at intervals of about 15 min in the post-midnight sector (01:55–02:40 MLT) by all-sky imagers and magnetometers in northern Europe. It was deduced that each surge occurred just after each onset of a multiple-onset substorm, which was small-scale and did not clearly expand westward, because they were observed almost simultaneously with Pi 2 pulsations at the magnetic equator and magnetic bay variations at middle-to-high latitudes associated with the DP-1 current system. The EEASs showed similar properties to omega bands or torches reported in previous studies, such as recurrence intervals of about 15 min, concurrence with magnetic pulsations with amplitudes of several tens of nanotesla, horizontal scales of 300–400 km, and occurrence of a pulsating aurora in a diffuse aurora after the passage of the EEASs. Furthermore, the EEASs showed similar temporal evolution to the omega bands, during which eastward-propagating auroral streamers occurred simultaneously in the poleward region, followed by the formation of north-south-aligned auroras, which eventually connected with the EEASs. Thus, we speculate that EEASs may be related to the generation process of omega bands. On the other hand, the EEASs we observed had several properties that were different from those of omega bands, such as greater eastward propagation speed (3–4 km/s), shorter associated magnetic pulsation periods (4–6 min), and a different ionospheric equivalent current direction. The fast eastward propagation speed of the EEASs is consistent with the speed of eastward expansion fronts of the substorm current wedge reported in previous studies. The difference in the ionospheric current between the EEASs and omega bands may be caused by a large temporal variation of the surge structure, compared with the more stable wavy structure of omega bands.
eastward-expanding auroral surges, auroral streamers, post-midnight sector, substorm expansion phase, omega bands, magnetic pulsations, ionospheric equivalent current
1343-8832
1-10
Tanaka, Yoshimasa
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Ogawa, Yasunobu
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Kadokura, Akira
98c3ba7e-656b-4c08-8f41-08134a490234
Partamies, Noora
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Whiter, Daniel
9a30d7b6-ea41-44fb-bd52-3ff1964eca5c
Enell, Carl-Fredrik
8e7aac1d-3b44-4b7b-8aa8-a943716ede26
Brändström, Urban
d7c6c76d-e905-4948-acad-76783aebcd85
Sergienko, Tima
3ec9fa04-af59-4f04-88de-f9b5c6c625bd
Gustavsson, Björn
d88050c7-3139-4b1f-a0c1-a70d7288a3b6
Kozlovsky, Alexander
d09eef82-72ab-4df9-83f7-5d5838307ca9
Miyaoka, Hiroshi
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Yoshikawa, Akimasa
d959adff-f7e6-4421-a49e-ded159677e00
Tanaka, Yoshimasa
84f4fa8e-e753-46b9-b869-adc0adf0ad4f
Ogawa, Yasunobu
85325b9b-6c1e-49a2-9b56-2cec15e5c852
Kadokura, Akira
98c3ba7e-656b-4c08-8f41-08134a490234
Partamies, Noora
7219021b-a268-41eb-8e75-80550b7cf78f
Whiter, Daniel
9a30d7b6-ea41-44fb-bd52-3ff1964eca5c
Enell, Carl-Fredrik
8e7aac1d-3b44-4b7b-8aa8-a943716ede26
Brändström, Urban
d7c6c76d-e905-4948-acad-76783aebcd85
Sergienko, Tima
3ec9fa04-af59-4f04-88de-f9b5c6c625bd
Gustavsson, Björn
d88050c7-3139-4b1f-a0c1-a70d7288a3b6
Kozlovsky, Alexander
d09eef82-72ab-4df9-83f7-5d5838307ca9
Miyaoka, Hiroshi
dfefc1da-4214-4454-bf3a-8a898d703eaf
Yoshikawa, Akimasa
d959adff-f7e6-4421-a49e-ded159677e00

Tanaka, Yoshimasa, Ogawa, Yasunobu, Kadokura, Akira, Partamies, Noora, Whiter, Daniel, Enell, Carl-Fredrik, Brändström, Urban, Sergienko, Tima, Gustavsson, Björn, Kozlovsky, Alexander, Miyaoka, Hiroshi and Yoshikawa, Akimasa (2015) Eastward-expanding auroral surges observed in the post-midnight sector during a multiple-onset substorm Earth Planets and Space, 67, (182), pp. 1-10. (doi:10.1186/s40623-015-0350-8).

Record type: Article

Abstract

We present three eastward-expanding auroral surge (EEAS) events that were observed intermittently at intervals of about 15 min in the post-midnight sector (01:55–02:40 MLT) by all-sky imagers and magnetometers in northern Europe. It was deduced that each surge occurred just after each onset of a multiple-onset substorm, which was small-scale and did not clearly expand westward, because they were observed almost simultaneously with Pi 2 pulsations at the magnetic equator and magnetic bay variations at middle-to-high latitudes associated with the DP-1 current system. The EEASs showed similar properties to omega bands or torches reported in previous studies, such as recurrence intervals of about 15 min, concurrence with magnetic pulsations with amplitudes of several tens of nanotesla, horizontal scales of 300–400 km, and occurrence of a pulsating aurora in a diffuse aurora after the passage of the EEASs. Furthermore, the EEASs showed similar temporal evolution to the omega bands, during which eastward-propagating auroral streamers occurred simultaneously in the poleward region, followed by the formation of north-south-aligned auroras, which eventually connected with the EEASs. Thus, we speculate that EEASs may be related to the generation process of omega bands. On the other hand, the EEASs we observed had several properties that were different from those of omega bands, such as greater eastward propagation speed (3–4 km/s), shorter associated magnetic pulsation periods (4–6 min), and a different ionospheric equivalent current direction. The fast eastward propagation speed of the EEASs is consistent with the speed of eastward expansion fronts of the substorm current wedge reported in previous studies. The difference in the ionospheric current between the EEASs and omega bands may be caused by a large temporal variation of the surge structure, compared with the more stable wavy structure of omega bands.

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Accepted/In Press date: 28 October 2015
Published date: 9 November 2015
Keywords: eastward-expanding auroral surges, auroral streamers, post-midnight sector, substorm expansion phase, omega bands, magnetic pulsations, ionospheric equivalent current
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 397222
URI: http://eprints.soton.ac.uk/id/eprint/397222
ISSN: 1343-8832
PURE UUID: 970737a8-0e83-4045-9996-5ecf2ee1c598
ORCID for Daniel Whiter: ORCID iD orcid.org/0000-0001-7130-232X

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Date deposited: 22 Jun 2016 13:27
Last modified: 17 Jul 2017 18:42

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Contributors

Author: Yoshimasa Tanaka
Author: Yasunobu Ogawa
Author: Akira Kadokura
Author: Noora Partamies
Author: Daniel Whiter ORCID iD
Author: Carl-Fredrik Enell
Author: Urban Brändström
Author: Tima Sergienko
Author: Björn Gustavsson
Author: Alexander Kozlovsky
Author: Hiroshi Miyaoka
Author: Akimasa Yoshikawa

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