Evidence for non-Maxwellian electron energy distributions in the solar transition region: SiIII line ratios from SUMER

Recent calculations of Si III emission-line strengths are compared with SUM ER observations from a quiet solar region a coronal hole, and an active reg ion. Diagnostic line ratios are used to derive T-e and N-e for the emitting plasma in each region, and good agreement between theory and observations is found. A major enhancement in the intensity of the 1313 Angstrom emissio n line is observed, as well as some evidence of a small decrease in the tem perature of maximum ionization fraction, as one moves from the coronal hole to the active region. Possible explanations for these effects are discusse d, and it is concluded that they may be caused by the presence of nontherma l electrons in the transition region.