The onset and association of CMEs with sigmoidal active regions

Previous studies of active regions characterised by Soft X-ray S or inverse-S morphology [Canfield et al., 1999], have found these regions to possess a higher probability of eruption. In such cases, CME launch has been inferred using X-ray proxies to indicate eruption. Active regions observed during 1997, previously categorised as both sigmoidal and eruptive [Canfield, 1999], have been selected for further study, incorporating SoHO-LASCO, SoHO-EIT and ground based H-alpha data. Our results allow re-classification into three main categories; sigmoidal, non-sigmoidal and active regions appearing sigmoidal due to the projection of many loops. Although the reduced dataset size prevents a statistical measure of significance, we note that regions comprising a single S (or inverse-S) shaped structure are more frequently associated with a CME than those classed as non-sigmoidal. This motivates the study of a larger dataset and highlights the need for a quantitative observational definition of the term "sigmoid".