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Galactic cosmic ray H and He nuclei energy spectra measured by Voyagers 1 and 2 near the heliospheric termination shock in positive and negative solar magnetic polarity cycles

Webber, W. R. and Cummings, A. C. and McDonald, F. B. and Stone, E. C. and Heikkila, B. and Lal, N. (2008) Galactic cosmic ray H and He nuclei energy spectra measured by Voyagers 1 and 2 near the heliospheric termination shock in positive and negative solar magnetic polarity cycles. Journal of Geophysical Research A, 113 (A10). A10108. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:WEBjgra08

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Abstract

Using data from the Voyager 1 and 2 spacecraft, we have followed the intensity variations of H, He and C + O nuclei between 1998 and 2008 and determined the spectra for H and He at the time of minimum modulation in 1998, when the solar magnetic polarity was positive and again in 2008 when the solar magnetic polarity was negative. At these times these data are representative of conditions near a heliospheric termination shock assumed to be located at ∼90 AU. Above ∼400 MeV/nuc for He nuclei the 11-year solar modulation cycle observed at the Earth is not seen; instead there is a 22-year variation. The negative polarity cycle intensities above ∼150 MeV/nuc are higher than those in the positive polarity cycle by a factor of 1.4–1.7 times for both H and He nuclei. Below ∼100 MeV/nuc the C nuclei intensities are similar in the two cycles to within ±10%. These observations are compared with theoretical calculations which also show a negative to positive polarity cycle intensity difference at higher energies, most likely associated with energy changes due to drifts near the termination shock, but the comparison suggests that improved estimates of the local interstellar spectra are required.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1029/2008JA013395DOIArticle
Additional Information:Copyright 2008 by the American Geophysical Union. Received 15 May 2008; revised 24 July 2008; accepted 4 August 2008; published 28 October 2008. Zuyin Pu thanks Lennard A. Fisk and another reviewer for their assistance in evaluating this paper.
Group:Space Radiation Laboratory
Subject Keywords:cosmic rays, termination shock, solar magnetic polarity
Record Number:CaltechAUTHORS:WEBjgra08
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:WEBjgra08
Official Citation:Webber, W. R., A. C. Cummings, F. B. McDonald, E. C. Stone, B. Heikkila, and N. Lal (2008), Galactic cosmic ray H and He nuclei energy spectra measured by Voyagers 1 and 2 near the heliospheric termination shock in positive and negative solar magnetic polarity cycles, J. Geophys. Res., 113, A10108, doi:10.1029/2008JA013395.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12881
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:08 Jan 2009 22:54
Last Modified:29 Jun 2015 14:55

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