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| Titel |
POLAR spacecraft observations of helium ion angular anisotropy in the Earth's radiation belts |
| VerfasserIn |
W. N. Spjeldvik, T. A. Fritz, J. Chen, R. B. Sheldon |
| 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 ; 17, no. 6 ; Nr. 17, no. 6, S.723-733 |
| Datensatznummer |
250013770
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| Publikation (Nr.) |
 copernicus.org/angeo-17-723-1999.pdf |
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| Zusammenfassung |
New observations of energetic helium ion
fluxes in the Earth's radiation belts have been obtained with the CAMMICE/HIT
instrument on the ISTP/GGS POLAR spacecraft during the extended geomagnetically
low activity period April through October 1996. POLAR executes a high
inclination trajectory that crosses over both polar cap regions and passes over
the geomagnetic equator in the heart of the radiation belts. The latter
attribute makes possible direct observations of nearly the full equatorial
helium ion pitch angle distributions in the heart of the Earth's radiation belt
region. Additionally, the spacecraft often re-encounters the same geomagnetic
flux tube at a substantially off-equatorial location within a few tens of
minutes prior to or after the equatorial crossing. This makes both the
equatorial pitch angle distribution and an expanded view of the local
off-equatorial pitch angle distribution observable. The orbit of POLAR also
permitted observations to be made in conjugate magnetic local time sectors over
the course of the same day, and this afforded direct comparison of observations
on diametrically opposite locations in the Earth's radiation belt region at
closely spaced times. Results from four helium ion data channels covering ion
kinetic energies from 520 to 8200 KeV show that the distributions display
trapped particle characteristics with angular flux peaks for equatorially
mirroring particles as one might reasonably expect. However, the helium ion
pitch angle distributions generally flattened out for equatorial pitch angles
below about 45°. Significant and systematic helium ion anisotropy difference at
conjugate magnetic local time were also observed, and we report quiet time
azimuthal variations of the anisotropy index.
Key words. Magnetospheric physics (energetic particles
· trapped; magnetospheric configuration and dynamics; plasmasphere) |
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