Cylindrical Symmetry of Sunspots as a Proxy for Flare-Related Changes in Pseudo-Vector Magnetic Field Derived from Line-of-Sight Magnetograms

Large-scale changes in the magnetic field twist and inclination in flaring regions are often observed in vector magnetograms. When vector data are not available, such changes can be investigated using proxies for vector magnetic fields derived from line-of-sight magnetograms. Longitudinal field is a projection of full vector field to the line-of-sight direction. Thus, it is possible to derive some information about the vector field from line-of-sight data in round sunspots, assuming that average properties of vector magnetic field in these sunspots depend mostly on distance from center of sunspot. Under this assumption, one can reconstruct vertical, radial, and tangential components of vector magnetic field using azimuthal averaging. We study changes in (pseudo-vector) magnetic fields, including twist and inclination of the magnetic fields, in sunspots associated with flare events using SDO/HMI longitudinal magnetograms. We compare the pseudo-vector results with SDO/HMI vector data.