Effect of the IMF B-y component on the ionospheric flow overhead at EISCAT: observations and theory
We have analysed a database of ∼300 h of tristatic ionospheric velocity measurements obtained overhead at Tromsø (66.3° magnetic latitude) by the EISCAT UHF radar system, for the presence of flow effects associated with the y-component of the IMF. Since it is already known that the flow depends upon...
Published in: | Annales Geophysicae |
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Main Authors: | , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)
2012
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Subjects: | |
Online Access: | http://hdl.handle.net/2381/18529 http://www.ann-geophys.net/18/1503/2000/angeo-18-1503-2000.html https://doi.org/10.1007/s005850000311 |
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ftleicester:oai:lra.le.ac.uk:2381/18529 |
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record_format |
openpolar |
institution |
Open Polar |
collection |
University of Leicester: Leicester Research Archive (LRA) |
op_collection_id |
ftleicester |
language |
English |
topic |
Science & Technology Physical Sciences Astronomy & Astrophysics Geosciences Multidisciplinary Meteorology & Atmospheric Sciences Geology magnetospheric physics magnetosphere-ionosphere interactions ionosphere plasma convection auroral ionosphere INTERPLANETARY MAGNETIC-FIELD CONVECTION CURRENTS CUSP MAGNETOSPHERE DEPENDENCE PATTERNS MODELS ORBIT POLAR |
spellingShingle |
Science & Technology Physical Sciences Astronomy & Astrophysics Geosciences Multidisciplinary Meteorology & Atmospheric Sciences Geology magnetospheric physics magnetosphere-ionosphere interactions ionosphere plasma convection auroral ionosphere INTERPLANETARY MAGNETIC-FIELD CONVECTION CURRENTS CUSP MAGNETOSPHERE DEPENDENCE PATTERNS MODELS ORBIT POLAR Khan, H. Cowley, S. W. H. Effect of the IMF B-y component on the ionospheric flow overhead at EISCAT: observations and theory |
topic_facet |
Science & Technology Physical Sciences Astronomy & Astrophysics Geosciences Multidisciplinary Meteorology & Atmospheric Sciences Geology magnetospheric physics magnetosphere-ionosphere interactions ionosphere plasma convection auroral ionosphere INTERPLANETARY MAGNETIC-FIELD CONVECTION CURRENTS CUSP MAGNETOSPHERE DEPENDENCE PATTERNS MODELS ORBIT POLAR |
description |
We have analysed a database of ∼300 h of tristatic ionospheric velocity measurements obtained overhead at Tromsø (66.3° magnetic latitude) by the EISCAT UHF radar system, for the presence of flow effects associated with the y-component of the IMF. Since it is already known that the flow depends upon IMF Bz, a least-squares multivariate analysis has been used to determine the flow dependence on both IMF By and Bz simultaneously. It is found that significant flow variations with IMF By occur, predominantly in the midnight sector (∼2100–0300 MLT), but also pre-dusk (∼1600–1700 MLT), which are directed eastward for IMF By positive and westward for IMF By negative. The flows are of magnitude 20–30 m s–1 nT–1 in the midnight sector, and smaller, 10–20 m s–1 nT–1, pre-dusk, and are thus associated with significant changes of flow of order a few hundred m s–1 over the usual range of IMF By of about ±5 nT. At other local times the IMF By-related perturbation flows are much smaller, less than ∼5 m s–1 nT–1, and consistent with zero within the uncertainty estimates. We have investigated whether these IMF By-dependent flows can be accounted for quantitatively by a theoretical model in which the equatorial flow in the inner magnetosphere is independent of IMF By, but where distortions of the magnetospheric magnetic field associated with a "penetrating" component of the IMF By field changes the mapping of the field to the ionosphere, and hence the ionospheric flow. We find that the principal flow perturbation produced by this effect is an east-west flow whose sense is determined by the north-south component of the unperturbed flow. Perturbations in the north-south flow are typically smaller by more than an order of magnitude, and generally negligible in terms of observations. Using equatorial flows which are determined from EISCAT data for zero IMF By, to which the corotation flow has been added, the theory predicts the presence of zonal perturbation flows which are generally directed eastward in the Northern Hemisphere for IMF By positive and westward for IMF By negative at all local times. However, although the day and night effects are therefore similar in principle, the model perturbation flows are much larger on the nightside than on the dayside, as observed, due to the day-night asymmetry in the unperturbed magnetospheric magnetic field. Overall, the model results are found to account well for the observed IMF By-related flow perturbations in the midnight sector, in terms of the sense and direction of the flow, the local time of their occurrence, as well as the magnitude of the flows (provided the magnetic model employed is not too distorted from dipolar form). At other local times the model predicts much smaller IMF By-related flow perturbations, and thus does not account for the effects observed in the pre-dusk sector. 42434 |
format |
Article in Journal/Newspaper |
author |
Khan, H. Cowley, S. W. H. |
author_facet |
Khan, H. Cowley, S. W. H. |
author_sort |
Khan, H. |
title |
Effect of the IMF B-y component on the ionospheric flow overhead at EISCAT: observations and theory |
title_short |
Effect of the IMF B-y component on the ionospheric flow overhead at EISCAT: observations and theory |
title_full |
Effect of the IMF B-y component on the ionospheric flow overhead at EISCAT: observations and theory |
title_fullStr |
Effect of the IMF B-y component on the ionospheric flow overhead at EISCAT: observations and theory |
title_full_unstemmed |
Effect of the IMF B-y component on the ionospheric flow overhead at EISCAT: observations and theory |
title_sort |
effect of the imf b-y component on the ionospheric flow overhead at eiscat: observations and theory |
publisher |
European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany) |
publishDate |
2012 |
url |
http://hdl.handle.net/2381/18529 http://www.ann-geophys.net/18/1503/2000/angeo-18-1503-2000.html https://doi.org/10.1007/s005850000311 |
long_lat |
ENVELOPE(-112.453,-112.453,57.591,57.591) |
geographic |
Tromsø The ''Y'' |
geographic_facet |
Tromsø The ''Y'' |
genre |
EISCAT Tromsø |
genre_facet |
EISCAT Tromsø |
op_source |
Web of Science http://webofknowledge.com |
op_relation |
ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES, 2001, 18 (12), pp. 1503-1522 0992-7689 http://hdl.handle.net/2381/18529 http://www.ann-geophys.net/18/1503/2000/angeo-18-1503-2000.html doi:10.1007/s005850000311 1432-0576 |
op_rights |
Archived with reference to SHERPA/RoMEO and publisher website. © European Geosciences Union 2001. Version of record:http://www.ann-geophys.net/18/1503/2000/angeo-18-1503-2000.html |
op_doi |
https://doi.org/10.1007/s005850000311 |
container_title |
Annales Geophysicae |
container_volume |
18 |
container_issue |
12 |
container_start_page |
1503 |
op_container_end_page |
1522 |
_version_ |
1766400296313946112 |
spelling |
ftleicester:oai:lra.le.ac.uk:2381/18529 2023-05-15T16:04:41+02:00 Effect of the IMF B-y component on the ionospheric flow overhead at EISCAT: observations and theory Khan, H. Cowley, S. W. H. 2012-10-24T09:05:42Z http://hdl.handle.net/2381/18529 http://www.ann-geophys.net/18/1503/2000/angeo-18-1503-2000.html https://doi.org/10.1007/s005850000311 English eng European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany) ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES, 2001, 18 (12), pp. 1503-1522 0992-7689 http://hdl.handle.net/2381/18529 http://www.ann-geophys.net/18/1503/2000/angeo-18-1503-2000.html doi:10.1007/s005850000311 1432-0576 Archived with reference to SHERPA/RoMEO and publisher website. © European Geosciences Union 2001. Version of record:http://www.ann-geophys.net/18/1503/2000/angeo-18-1503-2000.html Web of Science http://webofknowledge.com Science & Technology Physical Sciences Astronomy & Astrophysics Geosciences Multidisciplinary Meteorology & Atmospheric Sciences Geology magnetospheric physics magnetosphere-ionosphere interactions ionosphere plasma convection auroral ionosphere INTERPLANETARY MAGNETIC-FIELD CONVECTION CURRENTS CUSP MAGNETOSPHERE DEPENDENCE PATTERNS MODELS ORBIT POLAR Journal Article 2012 ftleicester https://doi.org/10.1007/s005850000311 2019-03-22T20:16:43Z We have analysed a database of ∼300 h of tristatic ionospheric velocity measurements obtained overhead at Tromsø (66.3° magnetic latitude) by the EISCAT UHF radar system, for the presence of flow effects associated with the y-component of the IMF. Since it is already known that the flow depends upon IMF Bz, a least-squares multivariate analysis has been used to determine the flow dependence on both IMF By and Bz simultaneously. It is found that significant flow variations with IMF By occur, predominantly in the midnight sector (∼2100–0300 MLT), but also pre-dusk (∼1600–1700 MLT), which are directed eastward for IMF By positive and westward for IMF By negative. The flows are of magnitude 20–30 m s–1 nT–1 in the midnight sector, and smaller, 10–20 m s–1 nT–1, pre-dusk, and are thus associated with significant changes of flow of order a few hundred m s–1 over the usual range of IMF By of about ±5 nT. At other local times the IMF By-related perturbation flows are much smaller, less than ∼5 m s–1 nT–1, and consistent with zero within the uncertainty estimates. We have investigated whether these IMF By-dependent flows can be accounted for quantitatively by a theoretical model in which the equatorial flow in the inner magnetosphere is independent of IMF By, but where distortions of the magnetospheric magnetic field associated with a "penetrating" component of the IMF By field changes the mapping of the field to the ionosphere, and hence the ionospheric flow. We find that the principal flow perturbation produced by this effect is an east-west flow whose sense is determined by the north-south component of the unperturbed flow. Perturbations in the north-south flow are typically smaller by more than an order of magnitude, and generally negligible in terms of observations. Using equatorial flows which are determined from EISCAT data for zero IMF By, to which the corotation flow has been added, the theory predicts the presence of zonal perturbation flows which are generally directed eastward in the Northern Hemisphere for IMF By positive and westward for IMF By negative at all local times. However, although the day and night effects are therefore similar in principle, the model perturbation flows are much larger on the nightside than on the dayside, as observed, due to the day-night asymmetry in the unperturbed magnetospheric magnetic field. Overall, the model results are found to account well for the observed IMF By-related flow perturbations in the midnight sector, in terms of the sense and direction of the flow, the local time of their occurrence, as well as the magnitude of the flows (provided the magnetic model employed is not too distorted from dipolar form). At other local times the model predicts much smaller IMF By-related flow perturbations, and thus does not account for the effects observed in the pre-dusk sector. 42434 Article in Journal/Newspaper EISCAT Tromsø University of Leicester: Leicester Research Archive (LRA) Tromsø The ''Y'' ENVELOPE(-112.453,-112.453,57.591,57.591) Annales Geophysicae 18 12 1503 1522 |