太阳磁结构中实际自由磁能和相对磁螺旋度预算计算的验证和基准
Validation and Benchmarking of a Practical Free Magnetic Energy and Relative Magnetic Helicity Budget Calculation in Solar Magnetic Structures
摘要：
在早期的工作中，我们介绍和测试了非线性无力（NLFF）的方法，旨在自洽地计算观测到的太阳磁结构的日冕的自由磁能和相对磁螺旋度预算。该方法需要，在原则上，只有一个单一的，光球或低色球，矢量磁图的一个安静的太阳补丁或一个活跃的地区，并进行计算的三维磁场和速度场信息的情况下。在这项工作中，我们严格验证这种方法使用三维冠状磁场。基准采用合成，三维磁流体动力学模拟和非线性无力场外推的活动区日冕。我们发现，我们的时间效率的NLFF方法提供的预算，不同于那些更苛刻的半分析方法的一个因素~3，最多。这种差异是从物理概念和方法的构建中预期的。时间相关性显示出更多的差异，然而，更复杂的，大规模的活动区域，达到相关系数的顺序，或超过0.9，是健全的改善。总之，我们认为，我们的NLFF方法可以可靠地用于常规和快速计算的自由磁能和相对磁螺旋预算在太阳磁化日冕的目标部分。正如在这里和以前的作品中所解释的那样，这是一种资产，可以导致对物理学和太阳爆发触发的宝贵见解。
英文摘要：
In earlier works we introduced and tested a nonlinear force-free (NLFF) method designed to self-consistently calculate the free magnetic energy and the relative magnetic helicity budgets of the corona of observed solar magnetic structures. The method requires, in principle, only a single, photospheric or low-chromospheric, vector magnetogram of a quiet-Sun patch or an active region and performs calculations in the absence of three-dimensional magnetic and velocity-field information. In this work we strictly validate this method using three-dimensional coronal magnetic fields. Benchmarking employs both synthetic, three-dimensional magnetohydrodynamic simulations and nonlinear force-free field extrapolations of the active-region solar corona. We find that our time-efficient NLFF method provides budgets that differ from those of more demanding semi-analytical methods by a factor of ~3, at most. This difference is expected from the physical concept and the construction of the method. Temporal correlations show more discrepancies that, however, are soundly improved for more complex, massive active regions, reaching correlation coefficients of the order of, or exceeding, 0.9. In conclusion, we argue that our NLFF method can be reliably used for a routine and fast calculation of free magnetic energy and relative magnetic helicity budgets in targeted parts of the solar magnetized corona. As explained here and in previous works, this is an asset that can lead to valuable insight into the physics and the triggering of solar eruptions.
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