Relative drift between black aurora and the ionospheric plasma
Black auroras are recognized as spatially well-defined regions within uniform diffuse aurora where the optical emission is significantly reduced. Although a well studied phenomenon, there is no generally accepted theory for black auroras. One theory suggests that black regions are formed when energe...
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Copernicus Publications
2005
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Online Access: | https://doi.org/10.5194/angeo-23-1611-2005 https://doaj.org/article/3bfc5a0ab66e42e1b2d777d8a0859c4a |
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ftdoajarticles:oai:doaj.org/article:3bfc5a0ab66e42e1b2d777d8a0859c4a 2023-05-15T16:04:49+02:00 Relative drift between black aurora and the ionospheric plasma E. M. Blixt M. J. Kosch J. Semeter 2005-07-01T00:00:00Z https://doi.org/10.5194/angeo-23-1611-2005 https://doaj.org/article/3bfc5a0ab66e42e1b2d777d8a0859c4a EN eng Copernicus Publications https://www.ann-geophys.net/23/1611/2005/angeo-23-1611-2005.pdf https://doaj.org/toc/0992-7689 https://doaj.org/toc/1432-0576 doi:10.5194/angeo-23-1611-2005 0992-7689 1432-0576 https://doaj.org/article/3bfc5a0ab66e42e1b2d777d8a0859c4a Annales Geophysicae, Vol 23, Pp 1611-1621 (2005) Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 article 2005 ftdoajarticles https://doi.org/10.5194/angeo-23-1611-2005 2022-12-31T04:35:21Z Black auroras are recognized as spatially well-defined regions within uniform diffuse aurora where the optical emission is significantly reduced. Although a well studied phenomenon, there is no generally accepted theory for black auroras. One theory suggests that black regions are formed when energetic magnetospheric electrons no longer have access to the loss cone. If this blocking mechanism drifts with the source electron population in the magnetosphere, black auroras in the ionosphere should drift eastward with a velocity that increases with the energy of the precipitating electrons in the surrounding aurora, since the gradient- B curvature drift is energy dependent. It is the purpose of this paper to test this hypothesis. To do so we have used simultaneous measurements by the European Incoherent Scatter (EISCAT) radar and an auroral TV camera at Tromsø, Norway. We have analyzed 8 periods in which a black aurora occurred frequently to determine their relative drift with respect to the ionospheric plasma. The black aurora was found to drift eastward with a velocity of 1.5–4km/s, which is in accordance with earlier observations. However, one case was found where a black patch was moving westward, this being the first report of such behaviour in the literature. In general, the drift was parallel to the ionospheric flow but at a much higher velocity. This suggests that the generating mechanism is not of ionospheric origin. The characteristic energy of the precipitating electron population was estimated through inversion of E -region plasma density profiles. We show that the drift speed of the black patches increased with the energy of the precipitating electrons in a way consistent with the gradient- B curvature drift, suggesting a magnetospheric mechanism for the black aurora. As expected, a comparison of the drift speeds with a rudimentary dipole field model of the gradient- B curvature drift speed only yields order-of-magnitude agreement, which most likely is due to the nightside disturbed magnetosphere being ... Article in Journal/Newspaper EISCAT Tromsø Directory of Open Access Journals: DOAJ Articles Norway Tromsø Annales Geophysicae 23 5 1611 1621 |
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Directory of Open Access Journals: DOAJ Articles |
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English |
topic |
Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 |
spellingShingle |
Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 E. M. Blixt M. J. Kosch J. Semeter Relative drift between black aurora and the ionospheric plasma |
topic_facet |
Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 |
description |
Black auroras are recognized as spatially well-defined regions within uniform diffuse aurora where the optical emission is significantly reduced. Although a well studied phenomenon, there is no generally accepted theory for black auroras. One theory suggests that black regions are formed when energetic magnetospheric electrons no longer have access to the loss cone. If this blocking mechanism drifts with the source electron population in the magnetosphere, black auroras in the ionosphere should drift eastward with a velocity that increases with the energy of the precipitating electrons in the surrounding aurora, since the gradient- B curvature drift is energy dependent. It is the purpose of this paper to test this hypothesis. To do so we have used simultaneous measurements by the European Incoherent Scatter (EISCAT) radar and an auroral TV camera at Tromsø, Norway. We have analyzed 8 periods in which a black aurora occurred frequently to determine their relative drift with respect to the ionospheric plasma. The black aurora was found to drift eastward with a velocity of 1.5–4km/s, which is in accordance with earlier observations. However, one case was found where a black patch was moving westward, this being the first report of such behaviour in the literature. In general, the drift was parallel to the ionospheric flow but at a much higher velocity. This suggests that the generating mechanism is not of ionospheric origin. The characteristic energy of the precipitating electron population was estimated through inversion of E -region plasma density profiles. We show that the drift speed of the black patches increased with the energy of the precipitating electrons in a way consistent with the gradient- B curvature drift, suggesting a magnetospheric mechanism for the black aurora. As expected, a comparison of the drift speeds with a rudimentary dipole field model of the gradient- B curvature drift speed only yields order-of-magnitude agreement, which most likely is due to the nightside disturbed magnetosphere being ... |
format |
Article in Journal/Newspaper |
author |
E. M. Blixt M. J. Kosch J. Semeter |
author_facet |
E. M. Blixt M. J. Kosch J. Semeter |
author_sort |
E. M. Blixt |
title |
Relative drift between black aurora and the ionospheric plasma |
title_short |
Relative drift between black aurora and the ionospheric plasma |
title_full |
Relative drift between black aurora and the ionospheric plasma |
title_fullStr |
Relative drift between black aurora and the ionospheric plasma |
title_full_unstemmed |
Relative drift between black aurora and the ionospheric plasma |
title_sort |
relative drift between black aurora and the ionospheric plasma |
publisher |
Copernicus Publications |
publishDate |
2005 |
url |
https://doi.org/10.5194/angeo-23-1611-2005 https://doaj.org/article/3bfc5a0ab66e42e1b2d777d8a0859c4a |
geographic |
Norway Tromsø |
geographic_facet |
Norway Tromsø |
genre |
EISCAT Tromsø |
genre_facet |
EISCAT Tromsø |
op_source |
Annales Geophysicae, Vol 23, Pp 1611-1621 (2005) |
op_relation |
https://www.ann-geophys.net/23/1611/2005/angeo-23-1611-2005.pdf https://doaj.org/toc/0992-7689 https://doaj.org/toc/1432-0576 doi:10.5194/angeo-23-1611-2005 0992-7689 1432-0576 https://doaj.org/article/3bfc5a0ab66e42e1b2d777d8a0859c4a |
op_doi |
https://doi.org/10.5194/angeo-23-1611-2005 |
container_title |
Annales Geophysicae |
container_volume |
23 |
container_issue |
5 |
container_start_page |
1611 |
op_container_end_page |
1621 |
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1766400444998877184 |