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| Titel |
Mesoscale structure of a morning sector ionospheric shear flow region determined by conjugate Cluster II and MIRACLE ground-based observations |
| VerfasserIn |
O. Amm, A. Aikio, J.-M. Bosqued, M. Dunlop, A. Fazakerley, P. Janhunen  , K. Kauristie, Mark Lester, I. Sillanpää, M. G. G. T. Taylor, A. Vontrat-Reberac, K. Mursula, M. André |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 21, no. 8 ; Nr. 21, no. 8, S.1737-1751 |
| Datensatznummer |
250014675
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| Publikation (Nr.) |
 copernicus.org/angeo-21-1737-2003.pdf |
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| Zusammenfassung |
We analyse a conjunction
event of the Cluster II spacecraft with the MIRACLE ground-based instrument
net-work in northern Fennoscandia on 6 February 2001, between 23:00 and 00:00
UT. Shortly after the spacecraft were located at perigee, the Cluster II
satellites’ magnetic footpoints move northwards over Scandinavia and Svalbard,
almost perfectly aligned with the central chain of the IMAGE magnetometer
network, and cross a morning sector ionospheric shear zone during this passage.
In this study we focus on the mesoscale structure of the ionosphere.
Ionospheric conductances, true horizontal currents, and field-aligned currents
(FAC) are calculated from the ground-based measurements of the IMAGE
magnetometers and the STARE coherent scatter radar, using the 1-D method of
characteristics. An excellent agreement between these results and the FAC
observed by Cluster II is reached after averaging the Cluster measurements to
mesoscales, as well as between the location of the convection reversal boundary
(CRB), as observed by STARE and by the Cluster II EFW instrument. A sheet of
downward FAC is observed in the vicinity of the CRB, which is mainly caused by
the positive divergence of the electric field there. This FAC sheet is detached
by 0.5°–2° of latitude from a more equatorward downward FAC sheet at the
poleward flank of the westward electrojet. This latter FAC sheet, as well as
the upward FAC at the equatorward flank of the jet, are mainly caused by
meridional gradients in the ionospheric conductances, which reach up to 25 S in
the electrojet region, but only ~ 5 S poleward of it, with a minimum at the CRB.
Particle measurements show that the major part of the downward FAC is carried
by upward flowing electrons, and only a small part by downward flowing ions.
The open-closed field line boundary is found to be located 3°–4° poleward
of the CRB, implying significant errors if the latter is used as a proxy of the
former.
Key words. Ionosphere (electric
fields and currents) – Magnetosphere physics (current systems; plasma
convection) |
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