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| Titel |
Mechanisms of the electron density depletion in the SAR arc region |
| VerfasserIn |
A. V. Pavlov |
| 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 ; 14, no. 2 ; Nr. 14, no. 2, S.211-221 |
| Datensatznummer |
250012170
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| Publikation (Nr.) |
 copernicus.org/angeo-14-211-1996.pdf |
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| Zusammenfassung |
| This study compares the measurements of
electron density and temperature and the integral airglow intensity at 630 nm in
the SAR arc region and slightly south of this (obtained by the Isis 2 spacecraft
during the 18 December 1971 magnetic storm), with the model results obtained
using the time dependent one-dimensional mathematical model of the Earth\'s
ionosphere and plasmasphere. The explicit expression in the third Enskog
approximation for the electron thermal conductivity coefficient in the
multicomponent mixture of ionized gases and a simplified calculation method for
this coefficient presents an opportunity to calculate more exactly the electron
temperature and density and 630 nm emission within SAR arc region are used in
the model. Collisions between N2 and hot thermal electrons in the SAR
arc region produce vibrationally excited nitrogen molecules. It appears that the
loss rate of O+(4S) due to reactions with the
vibrationally excited nitrogen is enough to explain electron density depression
by a factor of two at F-region heights and the topside ionosphere density
variations within the SAR arc if the erosion of plasma within geomagnetic field
tubes, during the main phase of the geomagnetic storm and subsequent filling of
geomagnetic tubes during the recovery phase, are considered. To explain the
disagreement by a factor 1.5 between the observed and modeled SAR arc electron
densities an additional plasma drift velocity ~–30 m s–1 in the ion
continuity equations is needed during the recovery phase. This additional plasma
drift velocity is likely caused by the transition from convecting to corotating
flux tubes on the equatorward wall of the trough. The electron densities and
temperatures and 630 nm integral intensity at the SAR arc and slightly south of
this region as measured for the 18 December 1971 magnetic storm were correctly
described by the model without perpendicular electric fields. Within this model
framework the effect of the perpendicular electric field ~100 mv m–1
with a duration ~1 h on the SAR arc electron density profiles was found to be
large. However, this effect is small if ~1–2 h have passed after the electric
field was set equal to zero. |
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