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.
Data availability
The GONG helioseismic phase-shift maps used in this study are publicly available through the National Solar Observatory (https://gong.nso.edu ). The SO/PHI line-of-sight magnetograms were obtained from the Solar Orbiter archive and are available upon request through the ESA Solar Orbiter data portal (https://soar.esac.esa.int ). The far-side active region masks, remapped magnetic maps, and derived analysis products generated in this study are available from the corresponding author upon reasonable request.
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Acknowledgements
AH and KJ were partially supported by the NSF Windows of the Universe - Multi-Messenger Astrophysics (WoU-MMA) grant to the National Solar Observatory. KJ also acknowledges partial support from NASA-DRIVE Center award 80NSSC20K0602 to Stanford. This work utilizes GONG data obtained by the NSO Integrated Synoptic Program, managed by the National Solar Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under a cooperative agreement with the National Science Foundation and with a contribution from the National Oceanic and Atmospheric Administration. The GONG network of instruments is hosted by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrofísica de Canarias, and Cerro Tololo Inter-American Observatory. Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. We are grateful to the ESA SOC and MOC teams for their support. The German contribution to SO/PHI is funded by the BMWi through DLR and by MPG central funds. The Spanish contribution is funded by AEI/MCIN/10.13039/501100011033/ (RTI2018-096886-C5, PID2021-125325OB-C5) and ERDF “A way of making Europe”; “Center of Excellence Severo Ochoa” awarded to IAA-CSIC (SEV-2017-0709, CEX2021-001131-S). The French contribution is funded by CNES.
Funding
KJ was partially supported by the NASA DRIVE Center award 80NSSC20K0602 to Stanford University. The German contribution to SO/PHI is funded by the BMWi through DLR and by MPG central funds. The Spanish contribution is funded by AEI/MCIN/10.13039/501100011033/ (RTI2018-096886-C5, PID2021-125325OB-C5) and ERDF “A way of making Europe”; “Center of Excellence Severo Ochoa” awarded to IAA-CSIC (SEV-2017-0709, CEX2021-001131-S). The French contribution is funded by CNES.
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K.J. designed the project and generated far-side helioseismic maps. H.S. and D.O.S calibrated SO/PHI data, selected the far side SO/PHI LoS magnetograms and remapped them to Carrington coordinates. A.H. developed the methodology, conducted the analysis and drafted the manuscript. A.H., K.J., and C.L. discussed the results and contributed to the manuscript. All authors reviewed and approved the final manuscript.
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Hamada, A., Jain, K., Strecker, H. et al. Polarity-resolved far-side magnetograms based on helioseismic measurements. Sci Rep (2026). https://doi.org/10.1038/s41598-026-42917-x
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DOI: https://doi.org/10.1038/s41598-026-42917-x
