Coronal magnetic field evolution over cycle 24
Coronal magnetic field evolution over cycle 24
复制标题
第 24 周期的日冕磁场演化
DOI：
10.1051/0004-6361/202038001
复制
发表时间：
2022
影响因子：
6.5
通讯作者：
Wiegelmann
中科院分区：
文献类型：
--
作者：
Inhester;Wiegelmann
背景光球磁场矢量是从测量中连续得到的，而三维(3D)日冕磁场的重建需要以光球测量为边界条件进行建模。几十年来，人们一直在研究光球层中磁场的周期变化。到目前为止，还没有关于日冕磁通量演化和太阳周期磁自由能演化的研究。目的分析24周日冕磁场和自由磁能的时间变化以及两个半球的磁场行为。为了模拟24周的磁场，我们将非线性无力场(NLFFF)优化方法应用于利用太阳动力学观测站(SDO)上的日球层和磁成像仪(HMI)观测得到的整套天气矢量磁图。结果根据我们的结果，我们发现在太阳24周期间，太阳动力学的最大值不同于太阳黑子数(SSN)的最大峰值。无符号通量的主要贡献来自−30°和+30°纬度内的磁场结构，而不是太阳黑子(MSO)。24周期间的磁通量变化在日冕和光球层表现出不同的演化。我们发现，从我们的模型得到的磁能与从观测得到的耀斑能量指数之间的关联值为0.8。平均而言，第24周在北半球(NH)有更多的太阳黑子，但在南半球(SH)有更强的通量，可以更有效地到达大气层的高层。两个半球之间的耦合随着高度的增加而增加。无符号磁通中最强的不对称性位于两个SSN峰之间。
ContextThe photospheric magnetic field vector is continuously derived from measurements, while reconstruction of the three-dimensional (3D) coronal magnetic field requires modelling with photospheric measurements as a boundary condition. For decades, the cycle variation of the magnetic field in the photosphere has been investigated. Until now, there has been no study of the evolution of the coronal magnetic flux in the corona or of the evolution of solar cycle magnetic free energy.AimsThe aim of this paper is to analyze the temporal variation of the magnetic field and free magnetic energy in the solar corona for solar cycle 24 and the behavior of the magnetic field in the two hemispheres. We want to investigate whether or not we can obtain better estimates of the magnetic field at Earth using the nonlinear force-free field extrapolation method.MethodsTo model the magnetic field over cycle 24 we apply the nonlinear force-free field (NLFFF) optimization method to the entire set of the synoptic vector magnetic maps derived from observations made using the Heliospheric and Magnetic Imager (HMI) on board Solar Dynamic Observatory (SDO).ResultsFrom our results, we find that during solar cycle 24, the maximum of the Sun’s dynamics is different than the sunspot number (SSN) maximum peak. The major contribution to the total unsigned flux is provided by the flux coming from the magnetic field structures other than sunspots (MSOS) within latitudes of −30° and +30°. The magnetic flux variation during solar cycle 24 shows a different evolution in the corona than in the photosphere. We find a correlation value of 0.8 between the derived magnetic energy from our model and the flare energy index derived from observations. On average, cycle 24 had a higher number of sunspots in the northern hemisphere (NH) but stronger flux in the southern hemisphere (SH) which could more effectively reach the higher layers of the atmosphere. The coupling between the hemispheres increases with height. The strongest asymmetries in the unsigned magnetic flux are between the two SSN peaks.