A Nonlinear Force-Free Magnetic Field Approximation Suitable for Fast Forward-Fitting to Coronal Loops. I. Theory
A Nonlinear Force-Free Magnetic Field Approximation Suitable for Fast Forward-Fitting to Coronal Loops. I. Theory
复制标题
DOI：
10.1007/s11207-012-0069-7
复制
发表时间：
2012-07
期刊：
影响因子：
2.8
通讯作者：
M. Aschwanden
中科院分区：
文献类型：
--
作者：
M. Aschwanden
基于二阶近似的非线性无力磁场解的均匀扭曲的磁力线在纸我，我们在这里开发了一个数值代码，能够向前拟合这样的解析解任意磁图（或矢量磁图）数据结合（立体三角形）冠环三维坐标。我们测试代码在这里通过前向拟合到六个势场和六个非势场的情况下模拟与我们的分析模型，以及通过前向拟合到一个完全无力的解决方案的低和娄（Astrophys. J.352，343，1990）模型。前向拟合测试表明：i）令人满意的收敛行为（典型的失准角为μ π ι 1 π ι- 10 π ι），ii）相对快速的计算时间（从几秒到几分钟），iii）检索到的无力α参数的高保真度（模拟的α拟合/α模型为0.9 - 1.0，Low和Lou模型的α拟合/α模型为0.7±0.3）。这个数字代码的显着特点是一个准无力磁场的计算相对较快，它密切匹配的几何形状的日冕环在活跃的地区，并补充现有的非线性无力场（NLFFF）代码的基础上光球磁没有日冕的限制。
Based on a second-order approximation of nonlinear force-free magnetic field solutions in terms of uniformly twisted field lines derived in Paper I, we develop here a numeric code that is capable to forward-fit such analytical solutions to arbitrary magnetogram (or vector magnetograph) data combined with (stereoscopically triangulated) coronal loop 3D coordinates. We test the code here by forward-fitting to six potential field and six nonpotential field cases simulated with our analytical model, as well as by forward-fitting to an exactly force-free solution of the Low and Lou (Astrophys. J.352, 343, 1990) model. The forward-fitting tests demonstrate: i) a satisfactory convergence behavior (with typical misalignment angles ofμ≈1∘– 10∘), ii) relatively fast computation times (from seconds to a few minutes), and iii) the high fidelity of retrieved force-freeα-parameters (αfit/αmodel≈0.9 – 1.0 for simulations andαfit/αmodel≈0.7±0.3 for the Low and Lou model). The salient feature of this numeric code is the relatively fast computation of a quasi-force-free magnetic field, which closely matches the geometry of coronal loops in active regions, and complements the existing nonlinear force-free field (NLFFF) codes based on photospheric magnetograms without coronal constraints.