EISCAT observations of unusual flows in the morning sector associated with weak substorm activity
A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geost...
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1994
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ftdoajarticles:oai:doaj.org/article:a427d2277ba24b44b7916c0e517e9a61 2023-05-15T16:04:26+02:00 EISCAT observations of unusual flows in the morning sector associated with weak substorm activity N. J. Fox M. Lockwood S. W. H. Cowley M. P. Freeman E. Friis-Christensen D. K. Milling M. Pinnock G. D. Reeves 1994-05-01T00:00:00Z https://doi.org/10.1007/s00585-994-0541-2 https://doaj.org/article/a427d2277ba24b44b7916c0e517e9a61 EN eng Copernicus Publications https://www.ann-geophys.net/12/541/1994/angeo-12-541-1994.pdf https://doaj.org/toc/0992-7689 https://doaj.org/toc/1432-0576 doi:10.1007/s00585-994-0541-2 0992-7689 1432-0576 https://doaj.org/article/a427d2277ba24b44b7916c0e517e9a61 Annales Geophysicae, Vol 12, Pp 541-553 (1994) Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 article 1994 ftdoajarticles https://doi.org/10.1007/s00585-994-0541-2 2022-12-31T16:11:29Z A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at ~0415 MLT) contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (~0515 MLT) with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is "pinched off", and present two alternative explanations in terms of (1) viscous and lobe circulation cells and (2) polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked "viscous-like" momentum transfer across the magnetopause. Article in Journal/Newspaper EISCAT Greenland Directory of Open Access Journals: DOAJ Articles Greenland Annales Geophysicae 12 6 541 553 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 |
spellingShingle |
Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 N. J. Fox M. Lockwood S. W. H. Cowley M. P. Freeman E. Friis-Christensen D. K. Milling M. Pinnock G. D. Reeves EISCAT observations of unusual flows in the morning sector associated with weak substorm activity |
topic_facet |
Science Q Physics QC1-999 Geophysics. Cosmic physics QC801-809 |
description |
A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at ~0415 MLT) contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (~0515 MLT) with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is "pinched off", and present two alternative explanations in terms of (1) viscous and lobe circulation cells and (2) polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked "viscous-like" momentum transfer across the magnetopause. |
format |
Article in Journal/Newspaper |
author |
N. J. Fox M. Lockwood S. W. H. Cowley M. P. Freeman E. Friis-Christensen D. K. Milling M. Pinnock G. D. Reeves |
author_facet |
N. J. Fox M. Lockwood S. W. H. Cowley M. P. Freeman E. Friis-Christensen D. K. Milling M. Pinnock G. D. Reeves |
author_sort |
N. J. Fox |
title |
EISCAT observations of unusual flows in the morning sector associated with weak substorm activity |
title_short |
EISCAT observations of unusual flows in the morning sector associated with weak substorm activity |
title_full |
EISCAT observations of unusual flows in the morning sector associated with weak substorm activity |
title_fullStr |
EISCAT observations of unusual flows in the morning sector associated with weak substorm activity |
title_full_unstemmed |
EISCAT observations of unusual flows in the morning sector associated with weak substorm activity |
title_sort |
eiscat observations of unusual flows in the morning sector associated with weak substorm activity |
publisher |
Copernicus Publications |
publishDate |
1994 |
url |
https://doi.org/10.1007/s00585-994-0541-2 https://doaj.org/article/a427d2277ba24b44b7916c0e517e9a61 |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
EISCAT Greenland |
genre_facet |
EISCAT Greenland |
op_source |
Annales Geophysicae, Vol 12, Pp 541-553 (1994) |
op_relation |
https://www.ann-geophys.net/12/541/1994/angeo-12-541-1994.pdf https://doaj.org/toc/0992-7689 https://doaj.org/toc/1432-0576 doi:10.1007/s00585-994-0541-2 0992-7689 1432-0576 https://doaj.org/article/a427d2277ba24b44b7916c0e517e9a61 |
op_doi |
https://doi.org/10.1007/s00585-994-0541-2 |
container_title |
Annales Geophysicae |
container_volume |
12 |
container_issue |
6 |
container_start_page |
541 |
op_container_end_page |
553 |
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1766400044391464960 |