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Published June 20, 2013 | Published
Journal Article Open

Galactic Cosmic-Ray Energy Spectra and Composition during the 2009-2010 Solar Minimum Period


We report new measurements of the elemental energy spectra and composition of galactic cosmic rays during the 2009-2010 solar minimum period using observations from the Cosmic Ray Isotope Spectrometer (CRIS) onboard the Advanced Composition Explorer. This period of time exhibited record-setting cosmic-ray intensities and very low levels of solar activity. Results are given for particles with nuclear charge 5 ≤ Z ≤ 28 in the energy range ~50-550 MeV nucleon^(–1). Several recent improvements have been made to the earlier CRIS data analysis, and therefore updates of our previous observations for the 1997-1998 solar minimum and 2001-2003 solar maximum are also given here. For most species, the reported intensities changed by less than ~7%, and the relative abundances changed by less than ~4%. Compared with the 1997-1998 solar minimum relative abundances, the 2009-2010 abundances differ by less than 2σ, with a trend of fewer secondary species observed in the more recent time period. The new 2009-2010 data are also compared with results of a simple "leaky-box" galactic transport model combined with a spherically symmetric solar modulation model. We demonstrate that this model is able to give reasonable fits to the energy spectra and the secondary-to-primary ratios B/C and (Sc+Ti+V)/Fe. These results are also shown to be comparable to a GALPROP numerical model that includes the effects of diffusive reacceleration in the interstellar medium.

Additional Information

© 2013 American Astronomical Society. Received 2013 February 14; accepted 2013 May 11; published 2013 June 3. This work was supported by NASA at the California Institute of Technology (under grants NNX08AI11G and NNX10AE45G), the Goddard Space Flight Center, the Jet Propulsion Laboratory, and Washington University in Saint Louis. We also acknowledge Dr. Nasser Barghouty for his vital help in updating the semi-empirical nuclear production cross sections used in our interstellar transport code.

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