Precision Measurements of Solar Energetic Particle Elemental Composition

Using data from the Cosmic Ray Subsystem aboard the Voyager 1 and 2 spacecraft (Stone et al., 1977), the authors have determined solar energetic particle abundances or upper limits for all elements with 3 ≤ Z ≤ 30 from a combined set of 10 solar flares during the 1977 - 1982 time period. Statistically meaningful abundances have been determined for the first time for several rare elements including P, Cl, K, Ti and Mn, while the precision of the mean abundances for the more abundant elements has been improved by typically a factor of ~3 over previously reported values. When compared to solar photospheric spectroscopic abundances, these new SEP abundances more clearly exhibit the step-function dependence on first ionization potential previously reported by Cook et al. (1979, 1984) and Meyer (1981, 1985).