A Comparison of ACE Measurements of Galactic Cosmic-Ray Abundances and Energy Spectra for Two Successive Solar Minima

Abstract

Using current solar minimum measurements from the Cosmic Ray Isotope Spectrometer (CRIS) onboard the Advanced Composition Explorer (ACE), we report the observed elemental abundances and energy spectra for C, O, Si, and Fe in the energy range of ~50-500MeV/nucleon. These measurements are compared to prior CRIS observations for the 1997-98 solar minimum period, when the solar magnetic field was of the opposite polarity. By April 2009, the current solar minimum intensities for each of the four elements has surpassed the peak intensities observed during the previous solar minimum. We also examine the correlation of the galactic cosmic ray intensities with the tilt angle of the heliospheric current sheet. These studies will be important for understanding solar modulation processes, such as changes in drift effects during a solar cycle.