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Evolution of the Energy Spectra of Anomalous Cosmic Rays in the Outer Heliosphere

Stone, E. C. and Cummings, A. C. and Webber, W. R. (1997) Evolution of the Energy Spectra of Anomalous Cosmic Rays in the Outer Heliosphere. In: Proceedings of the 25th International Cosmic Ray Conference. Vol.2. Potchefstroom University, Space Research Unit , Transvaal, South Africa, pp. 253-256.

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We present energy spectra of anomalous cosmic ray hydrogen, helium, and oxygen derived from data collected from experiments on the Voyager and Pioneer spacecraft from 1993 through 1996. The sequence of energy spectra show the effects of decreasing modulation as the solar cycle approaches and reaches solar minimum conditions. We suggest a number of factors that may be responsible for the spectral evolution, including the approach of the spacecraft to the source region of the particles (the solar wind termination shock), possible changes in the source strength, decreasing tilt of the neutral current sheet, and changes in the diffusion mean free path. We find that the data are inconsistent with source strength changes, but changes due to the other factors are possible and will require more complete 2 and 3-dimensional propagation models to make quantitative assessments. We find evidence for anomalous cosmic ray hydrogen up to energies as high as 400 MeV/nuc.

Item Type:Book Section
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Stone, E. C.0000-0002-2010-5462
Cummings, A. C.0000-0002-3840-7696
Additional Information:© Space Research Unit. Provided by the NASA Astrophysics Data System. This work was supported by NASA under contract NAS7-918.
Group:Space Radiation Laboratory
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Space Radiation Laboratory1997-07
Record Number:CaltechAUTHORS:20140703-225253772
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46857
Deposited By: Deborah Miles
Deposited On:15 Jul 2014 16:04
Last Modified:20 Feb 2020 14:33

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