Seeing the Invisible Sun: Reconstructing Far-Side Magnetograms from Helioseismology

Understanding and monitoring solar active regions is essential for operational space-weather forecasting and better solar dynamo modeling. This requires comprehensive 360$^\circ$ observations of the Sun. The front-side active regions are observed across multiple wavelengths,however, a critical gap in our knowledge remains due to the lack of direct, continuous magnetic field measurements of far-side active regions, specifically, magnetic field, polarity configurations and other parameters. We present a methodology for inferring magnetic field distributions of active regions in helioseismic maps of the far hemisphere. The crux of the analysis is the ability to realistically surmise the signs of the magnetic polarities of opposing components of a helioseismic signature. We present a method for stable, continuous polarity assignment of large-scale magnetic structures, derived from substructures that helioseismic signatures reliably resolve in strong active regions — particularly those that become space-weather hazards as solar rotation brings them into Earth’s view. Polarity boundaries are identified by analyzing the bi-modal longitudinal variance profile of the seismic signal within each region, after which Hale’s polarity rule is applied to establish east–west ordering consistent with the solar cycle. The method yields full-Sun magnetograms vital for coronal and solar-wind modeling, driving progress in heliospheric simulations and operational forecasting.