Abundances, spectra, and anisotropies in the 1998 Sep 30 and 2000 Apr 4 large Sep events

The 1998 Sep 30 and 2000 Apr 4 events are both large western solar energetic particle (SEP) events, in which ∼ 1 MeV proton intensities exceed 103 particles (cm2 s sr MeV)-1 . Yet they exhibit quite different time variations of elemental abundance ratios and energy spectra. Using a model of SEP transport through self-amplified interplanetary Alfv´en waves, we fit the simultaneous observations of protons and ions of helium, oxygen, and iron. We conclude that wave amplification by high energy protons largely account for the differences in the observed time histories.