R. A. Leske, C. M. S. Cohen, A. C. Cummings, R. A. Mewaldt, and E. C. Stone California Institute of Technology, Pasadena, CA 91125 USA P. L. Slocum and M. E. Wiedenbeck Jet Propulsion Laboratory, Pasadena, CA 91109 USA E. R. Christian and T. T. von Rosenvinge NASA/Goddard Space Flight Center, Greenbelt, MD 20771 USA
Anomalous cosmic rays (ACRs) provide a sensitive probe of the access of cosmic rays to the inner heliosphere, varying in intensity by more than two orders of magnitude during the course of the solar cycle. New data which are becoming available from ACE can provide a detailed record of ACR intensity and spectral changes on short (~ 1 day) time scales during the approach to solar maximum, which will help address issues of ACR modulation and transport. The elemental and isotopic composition of ACRs provides important information on the source or sources of these particles, while their ionic charge state composition and its energy dependence serves as a diagnostic of their acceleration time scale. We review measurements of the ACR elemental, isotopic, and charge state composition and spectra as determined at 1 AU by SAMPEX, ACE, Wind, and other spacecraft, and compare these measurements to models of the acceleration, modulation, and transport of ACRs.