Polarity-resolved far-side magnetograms based on helioseismic measurements

Abstract

Abstract 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. While space-weather forecasting has long relied successfully on high-quality observations of the Earth-facing hemisphere, a critical gap in global magnetic context remains due to the lack of direct, continuous magnetic field measurements of far-side active regions, specifically magnetic field strength, polarity configurations, and related 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 polarity-resolved far-side magnetograms that are suitable for integration with near-side observations, enabling the construction of full-Sun magnetic boundary conditions for coronal and solar-wind modeling, and providing a critical step toward improved heliospheric simulations and operational forecasting.