EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary
The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromsø (66.6° cgmLat) and Longyearbyen (75.2° cgmLat) on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar,...
Published in: | Annales Geophysicae |
---|---|
Main Authors: | , , , , , , , |
Format: | Text |
Language: | English |
Published: |
2018
|
Subjects: | |
Online Access: | https://doi.org/10.5194/angeo-26-87-2008 https://angeo.copernicus.org/articles/26/87/2008/ |
id |
ftcopernicus:oai:publications.copernicus.org:angeo36305 |
---|---|
record_format |
openpolar |
spelling |
ftcopernicus:oai:publications.copernicus.org:angeo36305 2023-05-15T16:04:35+02:00 EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary Aikio, A. T. Pitkänen, T. Fontaine, D. Dandouras, I. Amm, O. Kozlovsky, A. Vaivdas, A. Fazakerley, A. 2018-09-27 application/pdf https://doi.org/10.5194/angeo-26-87-2008 https://angeo.copernicus.org/articles/26/87/2008/ eng eng doi:10.5194/angeo-26-87-2008 https://angeo.copernicus.org/articles/26/87/2008/ eISSN: 1432-0576 Text 2018 ftcopernicus https://doi.org/10.5194/angeo-26-87-2008 2020-07-20T16:26:58Z The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromsø (66.6° cgmLat) and Longyearbyen (75.2° cgmLat) on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB) made zig-zag-type motion with amplitude of 2.5° cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL). The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992). The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm. During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4 R E mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H + and O + ions took place within the plasma sheet boundary layer (PSBL) as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be further energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency) fluctuations. The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2° during ~5 min. The beginning of the poleward motion of the PCB was associated with an intensification of the downward FAC at the boundary. We suggest that the downward FAC sheet at the PCB is the high-altitude counterpart of the Earthward flowing FAC produced in the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979) during a short-lived reconnection pulse. Text EISCAT Longyearbyen Tromsø Copernicus Publications: E-Journals Cowley ENVELOPE(-134.909,-134.909,60.518,60.518) Lockwood ENVELOPE(167.400,167.400,-84.150,-84.150) Longyearbyen Tromsø Annales Geophysicae 26 1 87 105 |
institution |
Open Polar |
collection |
Copernicus Publications: E-Journals |
op_collection_id |
ftcopernicus |
language |
English |
description |
The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromsø (66.6° cgmLat) and Longyearbyen (75.2° cgmLat) on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB) made zig-zag-type motion with amplitude of 2.5° cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL). The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992). The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm. During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4 R E mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H + and O + ions took place within the plasma sheet boundary layer (PSBL) as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be further energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency) fluctuations. The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2° during ~5 min. The beginning of the poleward motion of the PCB was associated with an intensification of the downward FAC at the boundary. We suggest that the downward FAC sheet at the PCB is the high-altitude counterpart of the Earthward flowing FAC produced in the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979) during a short-lived reconnection pulse. |
format |
Text |
author |
Aikio, A. T. Pitkänen, T. Fontaine, D. Dandouras, I. Amm, O. Kozlovsky, A. Vaivdas, A. Fazakerley, A. |
spellingShingle |
Aikio, A. T. Pitkänen, T. Fontaine, D. Dandouras, I. Amm, O. Kozlovsky, A. Vaivdas, A. Fazakerley, A. EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary |
author_facet |
Aikio, A. T. Pitkänen, T. Fontaine, D. Dandouras, I. Amm, O. Kozlovsky, A. Vaivdas, A. Fazakerley, A. |
author_sort |
Aikio, A. T. |
title |
EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary |
title_short |
EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary |
title_full |
EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary |
title_fullStr |
EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary |
title_full_unstemmed |
EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary |
title_sort |
eiscat and cluster observations in the vicinity of the dynamical polar cap boundary |
publishDate |
2018 |
url |
https://doi.org/10.5194/angeo-26-87-2008 https://angeo.copernicus.org/articles/26/87/2008/ |
long_lat |
ENVELOPE(-134.909,-134.909,60.518,60.518) ENVELOPE(167.400,167.400,-84.150,-84.150) |
geographic |
Cowley Lockwood Longyearbyen Tromsø |
geographic_facet |
Cowley Lockwood Longyearbyen Tromsø |
genre |
EISCAT Longyearbyen Tromsø |
genre_facet |
EISCAT Longyearbyen Tromsø |
op_source |
eISSN: 1432-0576 |
op_relation |
doi:10.5194/angeo-26-87-2008 https://angeo.copernicus.org/articles/26/87/2008/ |
op_doi |
https://doi.org/10.5194/angeo-26-87-2008 |
container_title |
Annales Geophysicae |
container_volume |
26 |
container_issue |
1 |
container_start_page |
87 |
op_container_end_page |
105 |
_version_ |
1766400182715416576 |