The response of ionospheric convection in the polar cap to substorm activity
We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°λ-78°λ. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substo...
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ftdoajarticles:oai:doaj.org/article:91ffd9ab02384bce8d6a38201c4f0722 2023-05-15T16:04:34+02:00 The response of ionospheric convection in the polar cap to substorm activity M. Lester M. Lockwood T. K. Yeoman S. W. H. Cowley H. Lühr R. Bunting C. J. Farrugia 1995-02-01T00:00:00Z https://doi.org/10.1007/s00585-995-0147-3 https://doaj.org/article/91ffd9ab02384bce8d6a38201c4f0722 EN eng Copernicus Publications https://www.ann-geophys.net/13/147/1995/angeo-13-147-1995.pdf https://doaj.org/toc/0992-7689 https://doaj.org/toc/1432-0576 doi:10.1007/s00585-995-0147-3 0992-7689 1432-0576 https://doaj.org/article/91ffd9ab02384bce8d6a38201c4f0722 Annales Geophysicae, Vol 13, Pp 147-158 (1995) Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 article 1995 ftdoajarticles https://doi.org/10.1007/s00585-995-0147-3 2022-12-30T21:58:20Z We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°λ-78°λ. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71°λ by the time of the expansion phase onset. A westward electrojet, centred at 65.4°λ, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1°λ at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the "distant" neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap boundary. Article in Journal/Newspaper EISCAT Directory of Open Access Journals: DOAJ Articles Annales Geophysicae 13 2 147 158 |
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Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
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ftdoajarticles |
language |
English |
topic |
Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 |
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Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 M. Lester M. Lockwood T. K. Yeoman S. W. H. Cowley H. Lühr R. Bunting C. J. Farrugia The response of ionospheric convection in the polar cap to substorm activity |
topic_facet |
Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 |
description |
We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°λ-78°λ. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71°λ by the time of the expansion phase onset. A westward electrojet, centred at 65.4°λ, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1°λ at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the "distant" neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap boundary. |
format |
Article in Journal/Newspaper |
author |
M. Lester M. Lockwood T. K. Yeoman S. W. H. Cowley H. Lühr R. Bunting C. J. Farrugia |
author_facet |
M. Lester M. Lockwood T. K. Yeoman S. W. H. Cowley H. Lühr R. Bunting C. J. Farrugia |
author_sort |
M. Lester |
title |
The response of ionospheric convection in the polar cap to substorm activity |
title_short |
The response of ionospheric convection in the polar cap to substorm activity |
title_full |
The response of ionospheric convection in the polar cap to substorm activity |
title_fullStr |
The response of ionospheric convection in the polar cap to substorm activity |
title_full_unstemmed |
The response of ionospheric convection in the polar cap to substorm activity |
title_sort |
response of ionospheric convection in the polar cap to substorm activity |
publisher |
Copernicus Publications |
publishDate |
1995 |
url |
https://doi.org/10.1007/s00585-995-0147-3 https://doaj.org/article/91ffd9ab02384bce8d6a38201c4f0722 |
genre |
EISCAT |
genre_facet |
EISCAT |
op_source |
Annales Geophysicae, Vol 13, Pp 147-158 (1995) |
op_relation |
https://www.ann-geophys.net/13/147/1995/angeo-13-147-1995.pdf https://doaj.org/toc/0992-7689 https://doaj.org/toc/1432-0576 doi:10.1007/s00585-995-0147-3 0992-7689 1432-0576 https://doaj.org/article/91ffd9ab02384bce8d6a38201c4f0722 |
op_doi |
https://doi.org/10.1007/s00585-995-0147-3 |
container_title |
Annales Geophysicae |
container_volume |
13 |
container_issue |
2 |
container_start_page |
147 |
op_container_end_page |
158 |
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1766400166371262464 |