太阳磁场理论外推研究进展

Progress in Solar Magnetic Field Extrapolation

太阳磁场是研究太阳物理的关键。目前对太阳磁场的精确测量只限于光球层。对日冕磁场结构的了解,则多是以观测的光球磁场作为边界条件,在某种理论模型下进行外推。势场模型、线性无力场模型和非线性无力场模型是无力场假设下的三种理论外推模型。文章介绍了太阳磁场理论外推的基本方法和最新进展,和对三种模型中使用较多的外推方法,列举了它们在天文研究中的一些应用,同时也简略讨论了外推方法中存在的一些问题。

Solar magnetic field is the predominant factor of the solar activities. Precise measurements of solar magnetic fields so far are stiU confined to the thin layer of solar photosphere. In order to understand the nature of the coronal magnetic fields, it becomes necessary to extrapolate the coronal magnetic fields based on theoretical models using observed photospheric magnetograms as boundary conditions. Taking force-free assumptions, three kinds of models are currently being used： the potential field （or current-free field） model, the linear force-free field （or constant-α force-free field） model, and the non-linear force-free （NLFF） field （or non-constant-α force-free field） model. Methods of extrapolations based on these three models are introduced, with specific examples given and their astrophysical applications mentioned. Progress and problems in the extrapolation methods are also briefly addressed.