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| Titel |
Energy–latitude dispersion patterns near the isotropy boundaries of energetic protons |
| VerfasserIn |
V. A. Sergeev, S. A. Chernyaeva, S. V. Apatenkov, N. Y. Ganushkina, S. V. Dubyagin |
| 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 ; 33, no. 8 ; Nr. 33, no. 8 (2015-08-31), S.1059-1070 |
| Datensatznummer |
250121240
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| Publikation (Nr.) |
 copernicus.org/angeo-33-1059-2015.pdf |
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| Zusammenfassung |
Non-adiabatic motion of plasma sheet protons causes
pitch-angle scattering and isotropic precipitation to the
ionosphere, which forms the proton auroral oval. This mechanism
related to current sheet scattering (CSS) provides a specific
energy–latitude dispersion pattern near the equatorward boundary
of proton isotropic precipitation (isotropy boundary, IB), with
precipitation sharply decreasing at higher (lower) latitude for
protons with lower (higher) energy. However, this boundary maps to
the inner magnetosphere, where wave-induced scattering may
provide different dispersion patterns as recently demonstrated by
Liang et al. (2014). Motivated by the potential usage of the IBs
for the magnetotail monitoring as well as by the need to better
understand the mechanisms forming the proton IB, we investigate
statistically the details of particle flux patterns near the
proton IB using NOAA-POES polar spacecraft observations made
during September 2009. By comparing precipitated-to-trapped flux
ratio (J0/J90) at >30 and >80 keV proton energies, we
found a relatively small number of simple CSS-type dispersion events
(only 31 %). The clear reversed (wave-induced) dispersion patterns
were very rare (5 %). The most frequent pattern had nearly
coinciding IBs at two energies (63 %). The structured precipitation with multiple IBs was very frequent (60 %), that is, with two
or more significant J0/J90 dropouts. The average latitudinal
width of multiple IB structures was about 1°. Investigation
of dozens of paired auroral zone crossings of POES satellites showed
that the IB pattern is stable on a timescale of less than 2 min (a few
proton bounce periods) but can evolve on a longer (several
minutes) scale, suggesting temporal changes in some mesoscale
structures in the equatorial magnetosphere.
We discuss the possible role of CSS-related and wave-induced
mechanisms and their possible coupling to interpret the emerging
complicated patterns of proton isotropy boundaries. |
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