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Published 1999 | Published
Book Section - Chapter Open

Time Variations of Solar Energetic Particle Abundances Observed by the ACE Spacecraft


The abundances of elements from Helium to Iron have been observed in nine different solar energetic particle (SEP) events using the Solar Isotope Spectrometer (SIS) on-board the Advanced Composition Explorer (ACE). SIS has a large geometry factor (~38 cm^2-sr), enabling us to observe abundances on a time scale of hours. In this paper we repo1t on substantial temporal variations of the observed abundances within events and from event to event. We wish to understand these results in terms of acceleration and transpo1t processes, taking into account factors such as first ionization potential, particle charge states, spectral shape, and event type (gradual and impulsive). It is essential that these variations be understood if we are to reliably estimate the composition of the sun from direct observations of SEP abundances.

Additional Information

© University of Utah. Provided by the NASA Astrophysics Data System. TvR thanks Donald Reames and Allan Tylka for instructive discussions on this topic. This work was supported by NASA at the California Institute of Technology (under grant NAG5-6912), the Jet Propulsion Laboratory, and the Goddard Space Flight Center.

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August 19, 2023
October 20, 2023