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| Titel |
A case study of electron precipitation in the late substorm growth phase on and nearby a preonset arc |
| VerfasserIn |
A. Olsson, P. Janhunen  |
| 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 ; 16, no. 12 ; Nr. 16, no. 12, S.1567-1572 |
| Datensatznummer |
250013594
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| Publikation (Nr.) |
 copernicus.org/angeo-16-1567-1998.pdf |
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| Zusammenfassung |
We follow the electron precipitation
characteristics on and nearby a preonset arc using the high resolution Freja
TESP instrument. Our data coverage extends from about 10 min before onset up to
1 min before onset. The arc is the most equatorward one (around MLAT 62°)
of a system of growth phase arcs, and it was close to the radiation belt
precipitation. Within the preonset arc, inverted-V type precipitation dominates.
Poleward of the arc we also find some precipitation regions, and here there is
systematically a cold electron population superposed with a warm population.
Using single and double Maxwellian fits to the measured electron spectra we find
the ionosphere-magnetosphere coupling parameters (field-aligned conductance K
and the parallel potential drop V) as well as the effective source plasma
properties (density and temperature) during the event. Compared to typical
expansion phase features, the preonset parallel potential drop is smaller by a
factor of ten, the electron temperature is smaller by a factor of at least five,
and the field-aligned conductance is about the same or larger. The fact that
there are two isotropic superposed electron populations on the poleward side of
the preonset arc suggests that the distance between warm trapped electrons on
dipolar field lines and colder electrons on open field lines has become so small
near the onset that mixing e.g. due to finite electron Larmor radius effects can
take place.
Key words. Ionosphere · (ionosophere-magnetosphere
interactions) · Magnetospheric physics (auroral phenomena; storms and
substorms). |
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