Sigmoidal Active Regions on the Sun: Statistical and Detailed Studies

We have compiled a catalog of sigmoidal active regions occurring in Aug 2010 - May 2012. The catalog data will enable us to identify variations and unifying characteristics of the sigmoids. In the long run, analyzing the typical behavior of these regions will improve space weather forecasting capabilities because sigmoidal regions have been shown to be a good predictor of eruptions. Additionally, we modeled the magnetic field of one of the cataloged sigmoids (NOAA active region 11474 at 2012.05.08/05:38:00) four hours prior to an eruption. The models consisted of a flux rope in a potential arcade, with the path of the rope following the H-α filament. The best fit model yields a current distribution which, viewed in cross section, exhibits a characteristic teardrop-shaped topology. Field lines passing through specific zones in the cross section define unique shapes in the sigmoid: the single S, the two Js, the overlying potential arcade, and the underlying small loops. The static model is slightly unstable; therefore, further relaxation of the model mimics the time evolution of the active region leading up to its eruption at 09:26. Future work will examine the relationship between Quasi-Separatrix Layer (QSL) maps and flare ribbons seen in 304Å images from the eruption.; Current and magnetic field lines from a model of a marginally stable flux rope. ; Cross section of the current. Note the x-line at the base of the flux rope.