ELEMENTAL ABUNDANCES OF FLARING SOLAR PLASMA - ENHANCED NEON AND SULFUR

Elemental abundances of two flares observed with the Solar Maximum Mis sion Flat Crystal Spectrometer are compared and contrasted. The first (a GOES Ml.5 flare) had a gradual rise and a slow decay, while the sec ond (a GOES M5 flare) was much more impulsive. Simultaneous spectra of seven bright soft X-ray resonance lines provide information over a br oad temperature range (2-35 x 10(6) K) and are available throughout bo th flares, making these events unique in the Solar Maximum Mission dat a base. Elemental abundances are investigated by means of a differenti al emission measure analysis. For the first flare, the plasma seemed t o be characterized by coronal abundances but, for the second, the plas ma composition could not be coronal, photospheric, or a linear combina tion of both. A good differential emission measure fit required enhanc ed neon such that Ne/O = 0.32 +/- 0.02, a value which is inconsistent with the current models of coronal abundances based on the elemental f irst-ionization potential, Similar values of enhanced neon are found f or flaring plasma observed by the Solar Maximum Mission gamma-ray spec trometer, in He-3-rich solar energetic particle events, and in the dec ay phase of several long duration soft X-ray events. Sulfur is also en hanced in the impulsive flare, but not as dramatically as neon. These events are compared with two models which attempt to explain the enhan ced values of neon and sulfur.