On compositional variations of heavy ions during solar particle events

Intensity-time profiles of protons, alpha particles, and heavy ions (C, O, Fe) in the MeV/nucleon energy range have been analyzed for one solar particle event following the solar flare on September 23, 1978. The data have been obtained with the wide angle double dE/dx-E sensor of the Max-Planck-Institut/University of Maryland experiment onboard ISEE-3. We found time variations in the iron to helium ratio of up to 2 orders of magnitude and a significant variation of the O/He ratio during this event, whereas the C/O-ratio at the same energy/nucleon appears to be time independent. We investigated the influence of a rigidity dependent mean free path in interplanetary space and of rigidity dependent coronal propagation on heavy ion ratios during solar particle events. We found that both the magnitude and time scale of the ratio changes during the September 23 event cannot be explained by rigidity dependent interplanetary or coronal propagation alone. These ratio changes are probably caused by multiple injection at the sun.