Optimization of Magnetic Flux Ropes Modeled with the Regularized Biot–Savart Law Method
Optimization of Magnetic Flux Ropes Modeled with the Regularized Biot–Savart Law Method
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DOI：
10.3847/1538-4365/abfe0f
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发表时间：
2021-06
期刊：
影响因子：
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通讯作者：
V. S. Titov;C. Downs;T. Török;J. Linker;R. Caplan;R. Lionello
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作者：
V. S. Titov;C. Downs;T. Török;J. Linker;R. Caplan;R. Lionello
正则化的毕奥-萨伐尔定律（RBSL）为模拟日冕物质抛射（CME）爆发前的磁位形提供了一种有效而灵活的方法，其特征受观测图像和磁场数据的约束。这种方法允许一个计算磁场的磁通绳（MFRs）与小圆形截面和任意轴形状。整个位形的场被构造为（1）这样的磁通绳场和（2）例如从观测到的磁图导出的环境势场的叠加。RBSL核是根据直圆柱体的MFR场必须完全无力的要求确定的。然而，对于弯曲的MFR，磁力在MFR的整个路径上通常是不平衡的。为了最大限度地减少这些力量，我们应用修改后的高斯-牛顿法找到最佳的MFR参数。这是通过迭代地调整MFR轴路径和轴向电流来完成的。然后，我们试图放松所得到的优化配置，在随后的线绑零β磁流体动力学模拟向无力平衡。通过考虑2009年2月13日CME的S形喷发前配置的两个模型，我们演示了这种方法是如何工作的，它是什么能力。我们表明，特别是，这些模型所描述的核心磁结构的构建块匹配通常在这种类型的配置中观察到的形态特征。我们的方法将是有用的建模特定的喷发事件和理论研究的理想化的喷发前MFR配置。
The so-called regularized Biot–Savart laws (RBSLs) provide an efficient and flexible method for modeling pre-eruptive magnetic configurations of coronal mass ejections (CMEs) whose characteristics are constrained by observational images and magnetic field data. This method allows one to calculate the field of magnetic flux ropes (MFRs) with small circular cross sections and an arbitrary axis shape. The field of the whole configuration is constructed as a superposition of (1) such a flux-rope field and (2) an ambient potential field derived, for example, from an observed magnetogram. The RBSL kernels are determined from the requirement that the MFR field for a straight cylinder must be exactly force free. For a curved MFR, however, the magnetic forces are generally unbalanced over the whole path of the MFR. To minimize these forces, we apply a modified Gauss–Newton method to find optimal MFR parameters. This is done by iteratively adjusting the MFR axis path and axial current. We then try to relax the resulting optimized configuration in a subsequent line-tied zero-beta magnetohydrodynamic simulation toward a force-free equilibrium. By considering two models of the sigmoidal pre-eruption configuration for the 2009 February 13 CME, we demonstrate how this approach works and what it is capable of. We show, in particular, that the building blocks of the core magnetic structure described by these models match morphological features typically observed in such types of configurations. Our method will be useful for both the modeling of particular eruptive events and theoretical studies of idealized pre-eruptive MFR configurations.