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We studied the developing conditions of sigmoid structure under the influenceof magnetic non-potential characteristics of a rotating sunspot in the activeregion (AR) 12158. Vector magnetic field measurements from HelioseismicMagnetic Imager and coronal EUV observations from Atmospheric Imaging Assemblyreveal that the erupting inverse-S sigmoid had roots in the location of therotating sunspot. Sunspot rotates at a rate of 0-5deg/h with increasing trendin the first half followed by a decrease. Time evolution of many non-potentialparameters had a well correspondence with the sunspot rotation. The evolutionof the AR magnetic structure is approximated by a time series of force freeequilibria. The NLFFF magnetic structure around the sunspot manifests theobserved sigmoid structure. Field lines from the sunspot periphery constitutethe body of the sigmoid and those from interior overly the sigmoid similar to afluxrope structure. While the sunspot is being rotating, two major CMEeruptions occurred in the AR. During the first (second) event, the coronalcurrent concentrations enhanced (degraded) consistent with the photospheric netvertical current, however the magnetic energy is released during both thecases. The analysis results suggest that the magnetic connections of thesigmoid are driven by slow motion of sunspot rotation, which transforms to ahighly twisted flux rope structure in a dynamical scenario. An exceedingcritical twist in the flux rope probably leads to the loss of equilibrium andthus triggering the onset of two eruptions.

Sunspot Rotation as a Driver of Major Solar Eruptions in NOAA Active Region 12158