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| Titel |
A very bright SAR arc: implications for extreme magnetosphere-ionosphere coupling |
| VerfasserIn |
J. Baumgardner, J. Wroten, J. Semeter, J. Kozyra, M. Buonsanto, P. Erickson, M. Mendillo |
| 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 ; 25, no. 12 ; Nr. 25, no. 12 (2008-01-02), S.2593-2608 |
| Datensatznummer |
250015965
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| Publikation (Nr.) |
 copernicus.org/angeo-25-2593-2007.pdf |
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| Zusammenfassung |
| In contrast to the polar aurora visible during geomagnetic storms, stable
auroral red (SAR) arcs offer a sub-visual manifestation of direct
magnetosphere-ionosphere (M-I) coupling at midlatitudes. The SAR arc emission
at 6300 Å is driven by field-aligned magnetospheric energy transport from
ring current/plasmapause locations into the ionosphere-thermosphere system.
The first SAR arc was observed at the dawn of the space age (1956), and the
typical brightness levels and occurrence patterns obtained from subsequent
decades of observations appear to be consistent with the downward heat
conduction theory, i.e., heated ambient F-layer electrons excite oxygen atoms
to produce a spectrally pure emission. On very rare occasions, a SAR arc has
been reported to be at brightness levels visible to the naked eye. Here we
report on the first case of a very bright SAR arc (~13 kilo-Rayleighs)
observed by four diagnostic systems that sampled various aspects of the
sub-auroral domain near Millstone Hill, MA, on the night of 29 October 1991:
an imaging spectrograph, an all-sky camera, an incoherent scatter radar
(ISR), and a DMSP satellite. Simulations of emission using the ISR and DMSP
data with the MSIS neutral atmosphere succeed in reproducing the brightness
levels observed. This provides a robust confirmation of M-I coupling theory
in its most extreme aeronomic form within the innermost magnetosphere
(L~2) during a rare superstorm event. The unusually high brightness
value appears to be due to the rare occurrence of the heating of dense
ionospheric plasma just equatorward of the trough/plasmapause location, in
contrast to the more typical heating of the less dense F-layer within the
trough. |
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