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We investigate the restructuring of the magnetic field in sunspots associatedwith two flares: the X6.5 flare on 6 December 2006 and the X2.2 flare on 15February 2011. The observed changes were evaluated with respect to theso-called twist-removal model, in which helicity (twist) is removed from thecorona as the result of an eruption. Since no vector magnetograms wereavailable for the X6.5 flare, we applied the azimuthal symmetry approach toline-of-sight magnetograms to reconstruct the pseudo-vector magnetic field andinvestigate the changes in average twist and inclination of magnetic field inthe sunspot around the time of the flare. For the X2.2 flare, results from thefull vector magnetograms were compared with the pseudo-vector field data. Forboth flares, the data show changes consistent with the twist-removal scenario.We also evaluate the validity of the azimuthal symmetry approach on simpleisolated round sunspots. In general, the derivations based on the azimuthalsymmetry approach agree with true-vector field data though we find that evenfor symmetric sunspots the distribution of the magnetic field may deviate froman axially symmetric distribution.

Search for a Signature of Twist-Removal in the Magnetic Field of Sunspots in Relation with Major Flares