Inferring Maps of the Sun’s Far-side Unsigned Magnetic Flux from Far-side Helioseismic Images Using Machine Learning Techniques

• Published in: The Astrophysical journal 2022-12, Vol.941 (2), p.197
• Main Authors: Chen, Ruizhu, Zhao, Junwei, Hess Webber, Shea, Liu, Yang, Hoeksema, J. Todd, DeRosa, Marc L.
• Format: Article
• Language: English
• Subjects: Astrophysics; Atmospheric models; Coronal magnetic fields; Fluctuations; Helioseismology; Machine learning; Magnetic fields; Magnetic flux; Modelling; Solar active regions; Solar activity; Solar corona; Solar magnetic field; Solar magnetic fields; Solar observatories; Solar wind; Solar wind structure; Space weather; Spatial resolution; Training
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aca333

Accurate modeling of the Sun’s coronal magnetic field and solar wind structures requires inputs of the solar global magnetic field, including both the near and far sides, but the Sun’s far-side magnetic field cannot be directly observed. However, the Sun’s far-side active regions are routinely monitored by helioseismic imaging methods, which only require continuous near-side observations. It is therefore both feasible and useful to estimate the far-side magnetic-flux maps using the far-side helioseismic images despite their relatively low spatial resolution and large uncertainties. In this work, we train two machine-learning models to achieve this goal. The first machine-learning training pairs simultaneous Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager-observed magnetic-flux maps and SDO/Atmospheric Imaging Assembly-observed extreme ultraviolet (EUV) 304 Å images, and the resulting model can convert 304 Å images into magnetic-flux maps. This model is then applied to the STEREO-observed far-side 304 Å images, available for about 4.3 yr, for the far-side magnetic-flux maps. These EUV-converted magnetic-flux maps are then paired with simultaneous far-side helioseismic images for a second machine-learning training, and the resulting model can convert far-side helioseismic images into magnetic-flux maps. These helioseismically derived far-side magnetic-flux maps, despite their limitations in spatial resolution and accuracy, can be routinely available on a daily basis, providing useful magnetic information on the Sun’s far side using only the near-side observations.