Statistical study of auroral fragmentation into patches
The study of auroral dynamics is important when considering disturbances of the magnetosphere. Shiokawa et al. (2010, 2014) reported observations of finger-like auroral structures that cause auroral fragmentation. Those structures are probably produced by macroscopic instabilities in the magnetosphe...
Published in: | Journal of Geophysical Research: Space Physics |
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ftleicester:oai:lra.le.ac.uk:2381/33002 2023-05-15T18:34:50+02:00 Statistical study of auroral fragmentation into patches Hashimoto, A. Shiokawa, K. Otsuka, Y. Oyama, S-I. Nozawa, S. Hori, T. Lester, Mark Johnsen, M. G. 2015-09-03T08:26:15Z http://onlinelibrary.wiley.com/doi/10.1002/2015JA021000/full http://hdl.handle.net/2381/33002 https://doi.org/10.1002/2015JA021000 en eng American Geophysical Union (AGU) Journal of Geophysical Research A: Space Physics, 2015 (Published ahead of print) 2169-9380 http://onlinelibrary.wiley.com/doi/10.1002/2015JA021000/full http://hdl.handle.net/2381/33002 doi:10.1002/2015JA021000 2169-9402 Copyright © 2015 American Geophysical Union. All Rights Reserved. An edited version of this paper was published by AGU. Copyright 2015 American Geophysical Union. Deposited with reference to the publisher’s open access archiving policy, available at http://publications.agu.org/author-resource-center/usage-permissions/#repository Aurora Auroral fragmentation Auroral patch Finger-like structures MHD instabilities Pressure-driven instability Journal Article Article in Press 2015 ftleicester https://doi.org/10.1002/2015JA021000 2019-03-22T20:20:27Z The study of auroral dynamics is important when considering disturbances of the magnetosphere. Shiokawa et al. (2010, 2014) reported observations of finger-like auroral structures that cause auroral fragmentation. Those structures are probably produced by macroscopic instabilities in the magnetosphere, mainly of the Rayleigh-Taylor type. However, the statistical characteristics of these structures have not yet been investigated. Here based on observations by an all-sky imager at Tromsø (magnetic latitude = 67.1°N), Norway, over three winter seasons, we statistically analyzed the occurrence conditions of 14 large-scale finger-like structures that developed from large-scale auroral regions including arcs and 6 small-scale finger-like structures that developed in auroral patches. The large-scale structures were seen from midnight to dawn local time and usually appeared at the beginning of the substorm recovery phase, near the low-latitude boundary of the auroral region. The small-scale structures were primarily seen at dawn and mainly occurred in the late recovery phase of substorms. The sizes of these large- and small-scale structures mapped in the magnetospheric equatorial plane are usually larger than the gyroradius of 10 keV protons, indicating that the finger-like structures could be caused by magnetohydrodynamic instabilities. However, the scale of small structures is only twice the gyroradius of 10 keV protons, suggesting that finite Larmor radius effects may contribute to the formation of small-scale structures. The eastward propagation velocities of the structures are -40 to +200 m/s and are comparable with those of plasma drift velocities measured by the colocating Super Dual Auroral Radar Network radar. Peer-reviewed Publisher Version Article in Journal/Newspaper Tromsø University of Leicester: Leicester Research Archive (LRA) Norway Tromsø Journal of Geophysical Research: Space Physics 120 8 6207 6217 |
institution |
Open Polar |
collection |
University of Leicester: Leicester Research Archive (LRA) |
op_collection_id |
ftleicester |
language |
English |
topic |
Aurora Auroral fragmentation Auroral patch Finger-like structures MHD instabilities Pressure-driven instability |
spellingShingle |
Aurora Auroral fragmentation Auroral patch Finger-like structures MHD instabilities Pressure-driven instability Hashimoto, A. Shiokawa, K. Otsuka, Y. Oyama, S-I. Nozawa, S. Hori, T. Lester, Mark Johnsen, M. G. Statistical study of auroral fragmentation into patches |
topic_facet |
Aurora Auroral fragmentation Auroral patch Finger-like structures MHD instabilities Pressure-driven instability |
description |
The study of auroral dynamics is important when considering disturbances of the magnetosphere. Shiokawa et al. (2010, 2014) reported observations of finger-like auroral structures that cause auroral fragmentation. Those structures are probably produced by macroscopic instabilities in the magnetosphere, mainly of the Rayleigh-Taylor type. However, the statistical characteristics of these structures have not yet been investigated. Here based on observations by an all-sky imager at Tromsø (magnetic latitude = 67.1°N), Norway, over three winter seasons, we statistically analyzed the occurrence conditions of 14 large-scale finger-like structures that developed from large-scale auroral regions including arcs and 6 small-scale finger-like structures that developed in auroral patches. The large-scale structures were seen from midnight to dawn local time and usually appeared at the beginning of the substorm recovery phase, near the low-latitude boundary of the auroral region. The small-scale structures were primarily seen at dawn and mainly occurred in the late recovery phase of substorms. The sizes of these large- and small-scale structures mapped in the magnetospheric equatorial plane are usually larger than the gyroradius of 10 keV protons, indicating that the finger-like structures could be caused by magnetohydrodynamic instabilities. However, the scale of small structures is only twice the gyroradius of 10 keV protons, suggesting that finite Larmor radius effects may contribute to the formation of small-scale structures. The eastward propagation velocities of the structures are -40 to +200 m/s and are comparable with those of plasma drift velocities measured by the colocating Super Dual Auroral Radar Network radar. Peer-reviewed Publisher Version |
format |
Article in Journal/Newspaper |
author |
Hashimoto, A. Shiokawa, K. Otsuka, Y. Oyama, S-I. Nozawa, S. Hori, T. Lester, Mark Johnsen, M. G. |
author_facet |
Hashimoto, A. Shiokawa, K. Otsuka, Y. Oyama, S-I. Nozawa, S. Hori, T. Lester, Mark Johnsen, M. G. |
author_sort |
Hashimoto, A. |
title |
Statistical study of auroral fragmentation into patches |
title_short |
Statistical study of auroral fragmentation into patches |
title_full |
Statistical study of auroral fragmentation into patches |
title_fullStr |
Statistical study of auroral fragmentation into patches |
title_full_unstemmed |
Statistical study of auroral fragmentation into patches |
title_sort |
statistical study of auroral fragmentation into patches |
publisher |
American Geophysical Union (AGU) |
publishDate |
2015 |
url |
http://onlinelibrary.wiley.com/doi/10.1002/2015JA021000/full http://hdl.handle.net/2381/33002 https://doi.org/10.1002/2015JA021000 |
geographic |
Norway Tromsø |
geographic_facet |
Norway Tromsø |
genre |
Tromsø |
genre_facet |
Tromsø |
op_relation |
Journal of Geophysical Research A: Space Physics, 2015 (Published ahead of print) 2169-9380 http://onlinelibrary.wiley.com/doi/10.1002/2015JA021000/full http://hdl.handle.net/2381/33002 doi:10.1002/2015JA021000 2169-9402 |
op_rights |
Copyright © 2015 American Geophysical Union. All Rights Reserved. An edited version of this paper was published by AGU. Copyright 2015 American Geophysical Union. Deposited with reference to the publisher’s open access archiving policy, available at http://publications.agu.org/author-resource-center/usage-permissions/#repository |
op_doi |
https://doi.org/10.1002/2015JA021000 |
container_title |
Journal of Geophysical Research: Space Physics |
container_volume |
120 |
container_issue |
8 |
container_start_page |
6207 |
op_container_end_page |
6217 |
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1766219803665629184 |