Wind/EPACT Observations of Temporal Evolution in Elemental Composition during Large Solar Energetic Particle Events
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON DC
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With a collecting power of 51 cm2-sr, the Low-Energy Matrix Telescope LEMT in the Wind satellites Energetic Particle Acceleration, Composition, and Transport EPACT experiment von Rosenvinge et al. 1995 Reames et al. 1997 provides unprecedented high-precision studies of the temporal evolution in elemental abundances during solar energetic particle SEP events at approximately 2-10 MeVnuc. We briefly review recently published studies of the 20 April 1998 SEP event Tylka, Reames, Ng 1999, which showed dramatic systematic compositional variation that can be largely understood in terms of transport through a time-dependent Alfven wavefield generated by the streaming energetic protons Ng, Reames, Tylka 1999. We compare those results to the 24 April 1999 SEP event, which was caused by a similar fast western coronal mass ejection CME but had a much softer proton spectrum, thereby leading to much weaker compositional variation. We also briefly comment on other events with different patterns of compositional evolution, which may also be significantly influenced by proton-generated waves.