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| Titel |
Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles |
| VerfasserIn |
A. G. Yahnin, V. A. Sergeev, B. B. Gvozdevsky, S. Vennerstrøm |
| 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 ; 15, no. 8 ; Nr. 15, no. 8, S.943-958 |
| Datensatznummer |
250012903
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| Publikation (Nr.) |
 copernicus.org/angeo-15-943-1997.pdf |
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| Zusammenfassung |
| According to observations, the discrete
auroral arcs can sometimes be found, either deep inside the auroral oval or at
the poleward border of the wide (so-called double) auroral oval, which map to
very different regions of the magnetotail. To find common physical conditions
for the auroral-arc generation in these magnetotail regions, we study the
spatial relationship between the diffuse and discrete auroras and the isotropic
boundaries (IBs) of the precipitating energetic particles which can be used to
characterise locally the equatorial magnetic field in the tail. From comparison
of ground observation of auroral forms with meridional profiles of particle flux
measured simultaneously by the low-altitude NOAA satellites above the ground
observation region, we found that (1) discrete auroral arcs are always situated
polewards from (or very close to) the IB of >30-keV electrons, whereas (2)
the IB of the >30-keV protons is often seen inside the diffuse aurora. These
relationships hold true for both quiet and active (substorm) conditions in the
premidnight-nightside (18-01-h) MLT sector considered. In some events the
auroral arcs occupy a wide latitudinal range. The most equatorial of these arcs
was found at the poleward edge of the diffuse auroras (but anyway in the
vicinity of the electron IB), the most poleward arcs were simultaneously
observed on the closed field lines near the polar-cap boundary. These
observations disagree with the notion that the discrete aurora originate
exclusively in the near-Earth portion of plasma sheet or exclusively on the PSBL
field lines. Result (1) may imply a fundamental feature of auroral-arc
formation: they originate in the current-sheet regions having very curved and
tailward-stretched magnetic field lines. |
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