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| Titel |
Statistical evidence for O+ energization and outflow caused by wave-particle interaction in the high altitude cusp and mantle |
| VerfasserIn |
M. Waara, R. Slapak, H. Nilsson, G. Stenberg, M. André, I. A. Barghouthi |
| 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 ; 29, no. 5 ; Nr. 29, no. 5 (2011-05-30), S.945-954 |
| Datensatznummer |
250017028
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| Publikation (Nr.) |
 copernicus.org/angeo-29-945-2011.pdf |
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| Zusammenfassung |
| We present a statistical study of the low (<1 Hz) frequency electric and
magnetic field spectral densities observed by Cluster spacecraft in the high
altitude cusp and mantle region. At the O+ gyrofrequency (0.02–0.5 Hz)
for this region the electric field spectral density is on average 0.2–2.2 (mV m−1)2 Hz−1,
implying that resonant heating at the gyrofrequency can be
intense enough to explain the observed O+ energies of 20–1400 eV. The
relation between the electric and magnetic field spectral densities results
in a large span of phase velocities, from a few hundred km s−1 up to a few
thousand km s−1. In spite of the large span of phase velocity, the ratio between
the calculated local Alfvén velocity and the estimated phase velocity is
close to unity. We provide average values of a coefficient describing
diffusion in ion velocity space at different altitudes, which can be used in
studies of ion energization and outflow. The observed average waves can
explain the average O+ energies measured in the high altitude (8–15 RE)
cusp/mantle region of the terrestrial magnetosphere according to our
test particle calculations. |
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