Nonlinear force-free modelling: influence of inaccuracies in the measured magnetic vector
Nonlinear force-free modelling: influence of inaccuracies in the measured magnetic vector
复制标题
非线性无力建模：测量的磁矢量误差的影响
DOI：
10.1051/0004-6361/200912812
复制
发表时间：
2009
影响因子：
6.5
通讯作者：
A. Lagg
中科院分区：
文献类型：
--
作者：
T. Wiegelmann;L. Y. Chaouche;S. Solanki;A. Lagg
上下文。太阳磁场经常外推到日冕中，从光球层的磁测量开始，这可能会受到重大不确定性的影响。目标。我们研究了由理想斯托克斯参数和噪声斯托克斯参数的反演在光球磁矢量图中引入的误差如何影响非线性无力磁场的外推。方法：研究方法。我们基于模拟的矢量磁图，通过对由三维辐射MHD模拟快照计算的斯托克斯剖面的反演，计算了非线性无力磁场。这些外推与在MHD模拟中直接起源于场的外推进行了比较，这是我们的参考。我们研究了谱线的形成和仪器效应，如噪声、有限的空间分辨率，以及使用滤波仪器的效果如何影响所产生的磁场结构。通过直观地检查磁场分布来定性地执行比较，并通过不同的度量来定量地进行比较。结果。如果对理想的斯托克斯数据进行反演，重建的场是最准确的，如果包括仪器效应和噪声，重建的场就变得不那么准确了。结果表明，在与现有仪器一致的水平上，本文所测试的非线性无力场外推方法对测量的偏振光谱中的噪声影响相对不敏感。结论。我们的结果表明，至少在没有太阳黑子的情况下，我们可以从实际的光球测量中将日冕磁场重建为非线性无力场，精度为几个百分点。
Context. Solar magnetic fields are regularly extrapolated into the corona starting from photospheric magnetic measurements that can be affected by significant uncertainty. Aims. We study how inaccuracies introduced into the maps of the photospheric magnetic vector by the inversion of ideal and noisy Stokes parameters influence the extrapolation of nonlinear force-free magnetic fields. Methods. We compute nonlinear force-free magnetic fields based on simulated vector magnetograms, by the inversion of Stokes profiles that were computed by a 3-D radiation MHD simulation snapshot. These extrapolations are compared with extrapolations that originate directly in the field in the MHD simulations, which is our reference. We investigate how line formation and instrumental effects such as noise, limited spatial resolution, and the effect of employing a filter instrument influence the resulting magnetic field structure. The comparison is performed qualitatively by visually inspecting the magnetic field distribution and quantitatively by different metrics. Results. The reconstructed field is most accurate if ideal Stokes data are inverted and becomes less accurate if instrumental effects and noise are included. The results demonstrate that the nonlinear force-free field extrapolation method tested here is relatively insensitive to the effects of noise in measured polarization spectra at levels consistent with present-day instruments. Conclusions. Our results show that we can reconstruct the coronal magnetic field as a nonlinear force-free field from realistic photospheric measurements with an accuracy of a few percent, at least in the absence of sunspots.