Composition of Solar Energetic Particle Events as  Measured by ACE/ULEIS

Joseph R. Dwyer

Abstract

Since its August 1997 launch, the Ultra-Low-Energy-Isotope (ULEIS) spectrometer onboard the ACE spacecraft has observed a large number of both gradual and impulsive solar energetic particle (SEP) events.  At 1 MeV/nucleon these events show remarkable variability of both the elemental and isotopic compositions.  We present new measurements of the 22Ne/20Ne ratio for these SEP events.  We have selected two subsets of the data according to whether 3He/4He > 0.01.  For the 3He-"poor" subset, we find that 22Ne/20Ne depends only weakly upon Fe/Mg and is marginally consistent with the solar wind value of 0.073.  The 22Ne/20Ne ratio for the 3He-"rich" subset, on the other hand, shows a significant correlation with Fe/Mg.  However, when compared with the elemental abundances, these variations in the 22Ne/20Ne ratio are much larger than expected from a simple charge to mass dependence, as was derived by Breneman & Stone (1985).

   Authors: J. R. Dwyer, G. M. Mason, J. E. Mazur, R. E. Gold and S.  M. Krimigis

  Organization: University of Maryland
     Telephone: 301-405-6208
           Fax: 301-314-9547
        e-mail: dwyer@uleis.umd.edu
       Address: Space Physics Group
   Department of Physics
   University of Maryland
   College Park, MD 20742