Ionic Charge States of Energetic Nuclei In Large Solar Particle Events

Data from SAMPEX and ACE acquired over solar cycle 23 have shown that in many large solar energetic particle (SEP) events associated with fast coronal mass ejections (typically referred to as gradual events), the mean ionic charge states of energetic nuclei from O to Fe increase with increasing kinetic energy. For example, in the November 6, 1997 event the mean charge state of Fe increased from +10 at 0.1 MeV/nucleon to +20 at energies >25 MeV/nucleon. The presence of highly ionized charge states appears to be correlated with the Fe/O ratio of the event. Several possibilities have been suggested for explaining the presence of highly ionized charge states, including: 1) the seed particle population includes remnant material from previous impulsive SEP events; 2) mixtures of flare and shock-accelerated ions from the same SEP event; and 3) electron stripping during the shock-acceleration process and subsequent transport to 1 AU. This talk will review the experimental data on ionic charge states in large SEP events and compare it with the predictions of these models.