Ionic Charge States of High Energy Solar Energetic Particles in Large Events

We present a novel technique to infer average ionic charge states of high energy (≥ 10 MeV/nuc) solar energetic particles (SEPs) in large solar events. In some large SEP events, it is observed that higher energy SEPs decay in intensity more rapidly than at lower energies. Furthermore, this energy dependence varies with particle species, as would be expected if the decay timescale depended on a rigidity-dependent diffusive mean free path. By comparing the decay timescales of nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron to a reference element, such as carbon, charge states are inferred for these elements in several SEP events between 1997 and 2002. There is considerable variation in the inferred charge state of iron from event to event. For the November 6, 1997 event, charge states are also inferred for sodium, calcium, and nickel.