Sigmoidal morphology and eruptive solar activity

Soft X-ray images of solar active regions frequently show S- or inverse-S ( sigmoidal) morphology. We have studied the Yohkoh Soft S-Ray Telescope vide o movie for 1993 and 1997. We have classified active regions according to m orphology (sigmoidal or non-sigmoidal) and nature of activity (eruptive or non-eruptive). As well, we have used NOAA sunspot areas for each region as a measure of size. We find that regions are significantly more likely to Le eruptive if they are either sigmoidal or large.