arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1807.06334astro-ph.SR
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太阳作为恒星的磁场矢量。II。通过活动周期24大尺度矢量场的演变

The magnetic field vector of the Sun-as-a-star. II. Evolution of the large-scale vector field through activity cycle 24

A. A. Vidotto, L. Lehmann, M. Jardine, A. Pevtsov

摘要:

在目前的工作中,我们调查如何大规模的太阳磁场,在其三个矢量分量,在大部分的周期24,从2010年1月到2018年4月的演变。为了过滤掉小规模的太阳场,目前在高分辨率的天气图,我们使用球谐分解方法,它分解的太阳场在多极与不同的l度。通过总结在一起的低-l多极,我们重建的大尺度场的分辨率类似于观察到的恒星磁场,这使得太阳和恒星的磁图之间的直接比较。在第24周期间,“太阳作为恒星”的磁场在径向和纬向分量中显示出极性反转,但在方位分量中没有。大尺度太阳场仍然主要是极向的,其能量的70%以上包含在极向分量中。在其演化过程中,当太阳黑子数接近极小值时,大尺度场更具有轴对称性和极向性,而在接近极大值时,大尺度场的强度更大。太阳的环向能量和黑子数之间存在着相关性,这表明黑子场是太阳环向大尺度能量的主要贡献者。太阳的大尺度磁性质与See等人报道的恒星磁性观测趋势相吻合,环向(Etor)和极向(Epol)能量的关系为Etor ~Epol^{1.38 \pm 0.04}。与恒星样品相似,太阳的大尺度场表现出缺乏环形非轴对称场。

英文摘要:

In the present work, we investigate how the large-scale magnetic field of the Sun, in its three vector components, has evolved during most of cycle 24, from 2010 Jan to 2018 Apr. To filter out the small-scale field of the Sun, present in high-resolution synoptic maps, we use a spherical harmonic decomposition method, which decomposes the solar field in multipoles with different l degrees. By summing together the low-l multipoles, we reconstruct the large-scale field at a resolution similar to observed stellar magnetic fields, which allows the direct comparison between solar and stellar magnetic maps. During cycle 24, the `Sun-as-a-star' magnetic field shows a polarity reversal in the radial and meridional components, but not in the azimuthal component. The large-scale solar field remains mainly poloidal with > 70% of its energy contained in the poloidal component. During its evolution, the large-scale field is more axisymmetric and more poloidal when near minima in sunspot numbers, and with a larger intensity near maximum. There is a correlation between toroidal energy and sunspot number, which indicates that spot fields are major contributors to the toroidal large-scale energy of the Sun. The solar large-scale magnetic properties fit smoothly with observational trends of stellar magnetism reported in See et al. The toroidal (Etor) and poloidal (Epol) energies are related as Etor ~Epol^{1.38 \pm 0.04}. Similar to the stellar sample, the large-scale field of the Sun shows a lack of toroidal non-axisymmetric field.

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