How Should One Optimize Nonlinear Force-Free Coronal Magnetic Field Extrapolations from SDO/HMI Vector Magnetograms?
How Should One Optimize Nonlinear Force-Free Coronal Magnetic Field Extrapolations from SDO/HMI Vector Magnetograms?
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DOI：
10.1007/s11207-012-9966-z
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发表时间：
2012-02
期刊：
影响因子：
2.8
通讯作者：
T. Wiegelmann;J. Thalmann;B. Inhester;T. Tadesse;Xudong Sun;J. Hoeksema
中科院分区：
文献类型：
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作者：
T. Wiegelmann;J. Thalmann;B. Inhester;T. Tadesse;Xudong Sun;J. Hoeksema
太阳动力学天文台（SDO）上的日震磁成像仪（HMI）提供了具有高空间和时间分辨率的光球矢量磁图。我们的目的是模拟日冕磁场以上的活动区域的非线性无力外推代码的帮助下。我们的代码是基于一个优化的原则，并已进行了广泛的测试，半解析和数值平衡，并适用于矢量磁图从日野和地面观测。最近，我们实施了一个新的版本，考虑到光球矢量磁图的测量误差。光球场的测量经常受到测量误差和有限的引力的影响，这些引力不适合作为日冕中无力场的边界。为了处理这些不确定性，我们开发了两个改进：i）表面测量的预处理，使它们与无力场兼容，和ii）新的代码，它保持了无力约束和光球场测量偏差之间的平衡。这两种方法都包含自由参数，必须对这些参数进行优化，以便与SDO/HMI数据一起使用。在这项工作中，我们描述了相应的分析方法，并评估如何以及力自由和螺线管条件的满足，由磁场和电流之间的角度，并通过比较投影的磁力线与冠状图像从大气成像组件（SDO/AIA）的无力平衡。我们还计算了可用的自由磁能，并讨论了控制参数的潜在影响。
TheHelioseismic and Magnetic Imager(HMI) on board theSolar Dynamics Observatory(SDO) provides photospheric vector magnetograms with a high spatial and temporal resolution. Our intention is to model the coronal magnetic field above active regions with the help of a nonlinear force-free extrapolation code. Our code is based on an optimization principle and has been tested extensively with semianalytic and numeric equilibria and applied to vector magnetograms fromHinodeand ground-based observations. Recently we implemented a new version which takes into account measurement errors in photospheric vector magnetograms. Photospheric field measurements are often affected by measurement errors and finite nonmagnetic forces inconsistent for use as a boundary for a force-free field in the corona. To deal with these uncertainties, we developed two improvements: i) preprocessing of the surface measurements to make them compatible with a force-free field, and ii) new code which keeps a balance between the force-free constraint and deviation from the photospheric field measurements. Both methods contain free parameters, which must be optimized for use with data from SDO/HMI. In this work we describe the corresponding analysis method and evaluate the force-free equilibria by how well force-freeness and solenoidal conditions are fulfilled, by the angle between magnetic field and electric current, and by comparing projections of magnetic field lines with coronal images from theAtmospheric Imaging Assembly(SDO/AIA). We also compute the available free magnetic energy and discuss the potential influence of control parameters.