Automatic Active-Region Identification and Azimuth Disambiguation of the SOLIS/VSM Full-Disk Vector Magnetograms

Abstract

The Vector Spectromagnetograph (VSM) of the NSO's Synoptic Optical Long-Term Investigations of the Sun (SOLIS) facility is now operational and obtains the first-ever vector magnetic field measurements of the entire visible solar hemisphere. To fully exploit the unprecedented SOLIS/VSM data, however, one must first address two critical problems: first, the study of solar active regions requires an automatic, physically intuitive, technique for active-region identification in the solar disk. Second, use of active-region vector magnetograms requires removal of the azimuthal $180^o$-ambiguity in the orientation of the transverse magnetic field component. Here we report on an effort to address both problems simultaneously and efficiently. To identify solar active regions we apply an algorithm designed to locate complex, flux-balanced, magnetic structures with a dominant E-W orientation on the disk. Each of the disk portions corresponding to active regions is thereafter extracted and subjected to the Nonpotential Magnetic Field Calculation (NPFC) method that provides a physically-intuitive solution of the 180-degree ambiguity. Both algorithms have been integrated into the VSM data pipeline and operate in real time, without human intervention. We conclude that this combined approach can contribute meaningfully to our emerging capability for full-disk vector magnetography as pioneered by SOLIS today and will be carried out by ground-based and space-borne magnetographs in the future.