Yang Dan, Heinemann Stephan G, Cameron Robert H, Gizon Laurent
Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany.
Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland.
Sol Phys. 2024;299(11):161. doi: 10.1007/s11207-024-02405-9. Epub 2024 Nov 27.
Maps of the magnetic field at the Sun's surface are commonly used as boundary conditions in space-weather modeling. However, continuous observations are only available from the Earth-facing part of the Sun's surface. One commonly used approach to mitigate the lack of far-side information is to apply a surface flux transport (SFT) model to model the evolution of the magnetic field as the Sun rotates. Helioseismology can image active regions on the far side using acoustic oscillations and hence has the potential to improve the modeled surface magnetic field. In this study, we propose a novel approach for estimating magnetic fields of active regions on the Sun's far side based on seismic measurements and then include them into an SFT model. To calibrate the conversion from helioseismic signal to magnetic field, we apply our SFT model to line-of-sight magnetograms from Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to obtain reference maps of global magnetic fields (including the far side). The resulting magnetic maps are compared with helioseismic phase maps on the Sun's far side computed using helioseismic holography. The spatial structure of the magnetic field within an active region is reflected in the spatial structure of the helioseismic phase shifts. We assign polarities to the unipolar magnetic-field concentrations based upon Hale's law and require approximate flux balance between the two polarities. From 2010 to 2024, we modeled 859 active regions, with an average total unsigned flux of Mx and an average area of km. Approximately of the active regions were found to have an anti-Hale configuration, which we manually corrected. Including these far-side active regions resulted in an average increase of (up to ) in the total unsigned magnetogram flux. Comparisons between modeled open-field areas and EUV observations reveal a substantial improvement in agreement when far-side active regions are included. This proof of concept study demonstrates the potential of the "combined surface flux transport and helioseismic Far-side Active Region Model" (FARM) to improve space-weather modeling.
太阳表面磁场图通常被用作空间天气建模的边界条件。然而，连续观测仅可从太阳表面面向地球的部分获得。一种常用的方法来缓解远侧信息的缺乏，是应用表面通量传输（SFT）模型来模拟太阳旋转时磁场的演化。日震学可以利用声学振荡对远侧的活动区域成像，因此有潜力改善模拟的表面磁场。在本研究中，我们提出了一种基于地震测量估计太阳远侧活动区域磁场的新方法，然后将其纳入SFT模型。为了校准从日震信号到磁场的转换，我们将我们的SFT模型应用于太阳动力学观测台（SDO）上搭载的日震和磁成像仪（HMI）的视线磁图，以获得全球磁场（包括远侧）的参考图。将得到的磁图与使用日震全息术计算的太阳远侧日震相位图进行比较。活动区域内磁场的空间结构反映在日震相移的空间结构中。我们根据黑尔定律为单极磁场集中区域指定极性，并要求两个极性之间的通量大致平衡。从2010年到2024年，我们对859个活动区域进行了建模，平均总无符号通量为 麦克斯韦，平均面积为 平方千米。发现大约 的活动区域具有反黑尔构型，我们对其进行了人工校正。纳入这些远侧活动区域导致总无符号磁图通量平均增加了 （最高可达 ）。对模拟的开放场区域与极紫外观测之间的比较表明，当纳入远侧活动区域时，一致性有了显著改善。这项概念验证研究证明了“表面通量传输与日震远侧活动区域联合模型”（FARM）在改善空间天气建模方面的潜力。
