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The Energy Spectra of Anomalous Cosmic Rays in the Outer Heliosphere During 1991-1994

Stone, E. C. and Cummings, A. C. (1995) The Energy Spectra of Anomalous Cosmic Rays in the Outer Heliosphere During 1991-1994. Advances in Space Research, 16 (9). p. 363. ISSN 0273-1177. doi:10.1016/0273-1177(95)00370-T.

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Since the launch of the Voyager spacecraft in 1977, we have monitored the energy spectra of anomalous cosmic rays (ACRs) as a function of radial and latitudinal position over the course of the solar cycle, including two reversals of the Sun's magnetic field. The energy spectrum for ACR helium observed during the last solar minimum period in 1987 at approximately 23 AU showed a rather narrow peak at approximately 22 MeV/nuc. In 1978 at approximately 2 AU, this spectrum was much broader with a peak at lower energies, in agreement with theories of the acceleration and propagation of these particles which include curvature and gradient drift in the interplanetary magnetic field. Currently, in the outer heliosphere at the position of Voyager 1 (approximately 55 AU and 32 deg N), the energy spectrum of ACR helium has a peak energy at approximately 8 MeV/nuc, considerably lower than previously observed. At Voyager 2 (42 AU and 11 deg S), the energy spectrum is quite different, having a peak energy near 20 MeV/nuc. We will report on the evolution of the spectra of ACRs as observed by the instruments on the Voyager spacecraft as the fluxes again approach solar minimum levels, expected in 1994, and relate the observations to models of their propagation.

Item Type:Article
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URLURL TypeDescription
Stone, E. C.0000-0002-2010-5462
Cummings, A. C.0000-0002-3840-7696
Additional Information:Copyright © 1995 COSPAR. Published by Elsevier.
Group:Space Radiation Laboratory
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Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory1995-41
Issue or Number:9
Record Number:CaltechAUTHORS:20140620-162104120
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46409
Deposited By: Deborah Miles
Deposited On:23 Jun 2014 21:47
Last Modified:10 Nov 2021 17:25

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