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 X‐Ray Telescope video movie for 1993 and 1997. We have classified active regions according to morphology (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 be eruptive if they are either sigmoidal or large.