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| Titel |
Magnetospheric conditions near the equatorial footpoints of proton isotropy boundaries |
| VerfasserIn |
V. A. Sergeev, I. A. Chernyaev, V. Angelopoulos, N. Y. Ganushkina |
| 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. 12 ; Nr. 33, no. 12 (2015-12-09), S.1485-1493 |
| Datensatznummer |
250121276
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| Publikation (Nr.) |
 copernicus.org/angeo-33-1485-2015.pdf |
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| Zusammenfassung |
| Data from a cluster of three THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft during
February–March 2009 frequently provide an opportunity to
construct local data-adaptive magnetospheric models, which are
suitable for the accurate mapping along the magnetic field lines
at distances of 6–9 Re in the nightside magnetosphere. This
allows us to map the isotropy boundaries (IBs) of 30 and 80 keV
protons observed by low-altitude NOAA POES (Polar Orbiting Environmental Satellites) to the
equatorial magnetosphere (to find the projected isotropy boundary,
PIB) and study the magnetospheric conditions, particularly to
evaluate the ratio KIB (Rc/rc; the magnetic field curvature radius to
the particle gyroradius) in the neutral sheet at that point.
Special care is taken to control the factors which influence the
accuracy of the adaptive models and mapping. Data indicate that
better accuracy of an adaptive model is achieved when the PIB
distance from the closest spacecraft is as small as 1–2 Re. For
this group of most accurate predictions, the spread of KIB
values is still large (from 4 to 32), with the median value
KIB ~13 being larger than the critical value Kcr ~ 8
expected at the inner boundary of nonadiabatic angular scattering
in the current sheet. It appears that two different mechanisms
may contribute to form the isotropy boundary. The group with
K ~ [4,12] is most likely formed by current sheet scattering,
whereas the group having KIB ~ [12,32] could be formed by
the resonant scattering of low-energy protons by the electromagnetic ion-cyclotron (EMIC) waves.
The energy dependence of the upper K limit and close proximity of
the latter event to the plasmapause locations support this
conclusion. We also discuss other reasons why the K ~ 8
criterion for isotropization may fail to work, as well as a
possible relationship between the two scattering mechanisms. |
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