E-region echo characteristics governed by auroral arc electrodynamics

Observations of a pair of auroral arc features by two imagers, one ground- and one space-based, allows the associated field-aligned current (FAC) and electric field structure to be inferred. Simultaneous observations of HF radar echoes provide an insight into the irregularity-generating mech...

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Main Authors: S. E. Milan, N. Sato, M. Lester, Y. Murata, Y. Shinkai, H. Doi, H. U. Frey, T. Saemundsson
Format: Article
Language:English
Published: Copernicus Publications 2003-07-01
Series:Annales Geophysicae
Online Access:https://www.ann-geophys.net/21/1567/2003/angeo-21-1567-2003.pdf
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spelling doaj-4731a63ea313452fbaf767206f7073c32020-11-24T22:24:37ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762003-07-01211567157510.5194/angeo-21-1567-2003E-region echo characteristics governed by auroral arc electrodynamicsS. E. Milan0N. Sato1M. Lester2Y. Murata3Y. Shinkai4H. Doi5H. U. Frey6T. Saemundsson7Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKNational Institute of Polar Research, Tokyo 173-8515, JapanDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKGraduate University for Advanced Studies, Tokyo 173-8515, JapanGraduate University for Advanced Studies, Tokyo 173-8515, JapanTokai University, Kanagawa 259-1292, JapanSpace Sciences Laboratory, University of California at Berkeley, California, USAScience Institute, University of Iceland, Reykjavik IS-107, IcelandObservations of a pair of auroral arc features by two imagers, one ground- and one space-based, allows the associated field-aligned current (FAC) and electric field structure to be inferred. Simultaneous observations of HF radar echoes provide an insight into the irregularity-generating mechanisms. This is especially interesting for the E-region echoes observed, which form the focus of our analysis, and from which several conclusions can be drawn, summarized as follows. Latitudinal variations in echo characteristics are governed by the FAC and electric field background. Particularly sharp boundaries are found at the edges of auroral arcs. Within regions of auroral luminosity, echoes have Doppler shifts below the ion-acoustic speed and are proportional to the electric field, suggesting scatter from gradient drift waves. Regions of downward FAC are associated with mixed high and low Doppler shift echoes. The high Doppler shift component is greatly in excess of the ion-acoustic speed, but seems to be commensurate with the driving electric field. The low Doppler shift component appears to be much depressed below expectations.<br><br><b>Key words. </b>Ionosphere (ionospheric irregularities; electric fields and currents)https://www.ann-geophys.net/21/1567/2003/angeo-21-1567-2003.pdf
collection DOAJ
language English
format Article
sources DOAJ
author S. E. Milan
N. Sato
M. Lester
Y. Murata
Y. Shinkai
H. Doi
H. U. Frey
T. Saemundsson
spellingShingle S. E. Milan
N. Sato
M. Lester
Y. Murata
Y. Shinkai
H. Doi
H. U. Frey
T. Saemundsson
E-region echo characteristics governed by auroral arc electrodynamics
Annales Geophysicae
author_facet S. E. Milan
N. Sato
M. Lester
Y. Murata
Y. Shinkai
H. Doi
H. U. Frey
T. Saemundsson
author_sort S. E. Milan
title E-region echo characteristics governed by auroral arc electrodynamics
title_short E-region echo characteristics governed by auroral arc electrodynamics
title_full E-region echo characteristics governed by auroral arc electrodynamics
title_fullStr E-region echo characteristics governed by auroral arc electrodynamics
title_full_unstemmed E-region echo characteristics governed by auroral arc electrodynamics
title_sort e-region echo characteristics governed by auroral arc electrodynamics
publisher Copernicus Publications
series Annales Geophysicae
issn 0992-7689
1432-0576
publishDate 2003-07-01
description Observations of a pair of auroral arc features by two imagers, one ground- and one space-based, allows the associated field-aligned current (FAC) and electric field structure to be inferred. Simultaneous observations of HF radar echoes provide an insight into the irregularity-generating mechanisms. This is especially interesting for the E-region echoes observed, which form the focus of our analysis, and from which several conclusions can be drawn, summarized as follows. Latitudinal variations in echo characteristics are governed by the FAC and electric field background. Particularly sharp boundaries are found at the edges of auroral arcs. Within regions of auroral luminosity, echoes have Doppler shifts below the ion-acoustic speed and are proportional to the electric field, suggesting scatter from gradient drift waves. Regions of downward FAC are associated with mixed high and low Doppler shift echoes. The high Doppler shift component is greatly in excess of the ion-acoustic speed, but seems to be commensurate with the driving electric field. The low Doppler shift component appears to be much depressed below expectations.<br><br><b>Key words. </b>Ionosphere (ionospheric irregularities; electric fields and currents)
url https://www.ann-geophys.net/21/1567/2003/angeo-21-1567-2003.pdf
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