Gamma-Ray Measurements of Flare-to-Flare Variations in Ambient Solar Abundances

We have measured uxes of ten narrow-ray lines in 19 X-class solar ares observed by the Solar Maximum Mission spectrometer from 1980 to 1989. These lines originate from interaction of energetic protons and-particles with ambient solar material. Flare-to-are variations in line uxes reveal that the abundances of elements in the are plasma are grouped with respect to their rst ionization potentials (FIP). Line uxes from elements with similar FIP's correlate well with one another; in contrast, the low-FIP (< 10 eV; Mg, Si, Fe) to high-FIP (>11 eV; C, N, O) line ratios vary by as much as about a factor of four from are to are. This factor of four is consistent with the enhancement of low-FIP elements found in the solar corona relative to photospheric abundances. We also nd that the Ne/O line ratio increases as the accelerated particle spectrum becomes softer. This can be explained by excitation cross sections <10 MeV, but the magnitude of the eeect is dependent on the accelerated-particle/proton ratio. After correcting for this spectral dependence, we nd that the Ne/(C + N + O) line ratio is constant from are-to-are, indicating that Ne behaves like these other high-FIP elements in the ambient are plasma. Based on these observations, we discuss a possible explanation for the factor of 3 enhancement in the abundance of Ne, relative to other high-FIP elements, in the 1981 April 27 are found by Murphy et al. (1991).