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Polar Spacecraft Observations of Helium Ion Angular Anisotropy in the Earth's Radiation Belts : Volume 17, Issue 6 (30/11/-0001)

By Spjeldvik, W. N.

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Book Id: WPLBN0004000595
Format Type: PDF Article :
File Size: Pages 11
Reproduction Date: 2015

Title: Polar Spacecraft Observations of Helium Ion Angular Anisotropy in the Earth's Radiation Belts : Volume 17, Issue 6 (30/11/-0001)  
Author: Spjeldvik, W. N.
Volume: Vol. 17, Issue 6
Language: English
Subject: Science, Annales, Geophysicae
Collections: Periodicals: Journal and Magazine Collection (Contemporary), Copernicus GmbH
Publication Date:
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications


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Sheldon, R. B., Chen, J., Spjeldvik, W. N., & Fritz, T. A. (-0001). Polar Spacecraft Observations of Helium Ion Angular Anisotropy in the Earth's Radiation Belts : Volume 17, Issue 6 (30/11/-0001). Retrieved from

Description: Physics Department, Weber State University, 2508 University Circle, Ogden, Utah 84408-2508, USA. 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)

POLAR spacecraft observations of helium ion angular anisotropy in the Earth's radiation belts


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