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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 110,
A12219,
doi:10.1029/2004JA010718,
2005
Comparison of energetic ions in cusp and outer radiation belt
Jiasheng Chen
Center for Space Physics, Boston University, Boston, Massachusetts, USA
Theodore A. Fritz
Center for Space Physics, Boston University, Boston, Massachusetts, USA
Robert B. Sheldon
NASA Marshall Space Flight Center, Huntsville, Alabama, USA
Abstract
Recently, large diamagnetic cavities with a size of as large as 6 Re have been observed in the dayside high-altitude cusp
regions. Associated with these cavities are charged particles with energies from 20 keV up to 10 MeV. Their seed population
is a mixture of ionospheric and solar wind particles. The energetic ion intensity, charge composition, energy spectrum, and
phase space density observed in the high-altitude dayside cusp have been compared with that measured in the outer radiation
belt over an energy range of 1–200 keV/e for protons and He++ ions and of 41–200 keV/e for O+ ions. It is found that (1) the shape of ion energy spectra in the cusp is different from that in the outer radiation belt,
(2) the ion phase space densities in the outer radiation belt are organized by magnetic moment, and (3) the ion phase space
density of both He++ and O+ in the cusp are higher than that in the outer radiation belt at a given magnetic moment. These results suggest that (1) the
measured cusp energetic ions cannot be explained by simple transport from an outer radiation belt (or ring current) source;
rather, (2) a nonadiabatic energization process would be required to relate the cusp energetic ion population to the belt
ion population, and (3) cusp energetic particles are potentially an additional independent source of the charged particles
in the outer radiation belt.
Received 3
August
2004;
accepted 27
September
2005;
published 20
December
2005.
Keywords: cusp;
radiation belts;
energetic particles;
magnetospheric configuration and dynamics;
solar wind/magnetosphere interactions.
Index Terms: 2706 Magnetospheric Physics: Cusp; 2720 Magnetospheric Physics: Energetic particles: trapped; 2731 Magnetospheric Physics: Magnetosphere: outer; 2774 Magnetospheric Physics: Radiation belts; 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics.
Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 1766354 bytes)
Citation: Chen, J., T. A. Fritz, and R. B. Sheldon
(2005),
Comparison of energetic ions in cusp and outer radiation belt,
J. Geophys. Res.,
110,
A12219,
doi:10.1029/2004JA010718.
Copyright 2005 by the American Geophysical Union.
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