Deducing the reliability of relative helicities from nonlinear force-free coronal models
Deducing the reliability of relative helicities from nonlinear force-free coronal models
复制标题
从非线性无力日冕模型推导相对螺旋度的可靠性
DOI：
10.1051/0004-6361/202038921
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发表时间：
2020-09
影响因子：
6.5
通讯作者：
J. Thalmann;Xudong Sun;K. Moraitis;M. Gupta
中科院分区：
文献类型：
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作者：
J. Thalmann;Xudong Sun;K. Moraitis;M. Gupta
目标。我们研究了活跃区 (AR) NOAA 12673 在十小时时间间隔内的相对螺旋度，该时间间隔以先前的 X2.2 耀斑 (SOL2017-09-06T08:57) 为中心，还包括三小时后发生的爆发性 X9.3 耀斑 (SOL2017-09-06T11:53)。特别是，我们的目标是对载流磁场的归一化自螺旋性进行可靠估计，即所谓的螺旋率|HJ|/|H𝒱|，它是量化太阳AR喷发潜力的一个有希望的候选者。方法。使用太阳动力学观测站日震和磁成像仪矢量磁场数据作为输入，我们采用优化方法采用非线性无力（NLFF）日冕磁场模型。使用有限体积方法计算相应的相对螺旋度和相关量。从基于不同自由模型参数选择的 NLFF 模型的多个时间序列中，我们能够评估 |HJ|/|H𝒱| 的分布，并估计其不确定性。结果。早期的工作将非螺线管对总磁能的贡献 Ediv/E 作为随后相对螺旋度分析所需的磁场模型螺线管质量的选择标准，与此相比，我们建议另外使用非螺线管对自由磁能的贡献 |Emix|/EJ, s。作为可靠估计相对磁螺旋度（和相关量）的方法，我们建议采用基于不同自由模型参数组合的多个 NLFF 模型，仅保留在某个时刻显示 Ediv/E 和 |Emix|/EJ, s 最小值的模型，以便随后计算平均估计值，并使用单独贡献值的分布作为不确定性的指示。
Aims. We study the relative helicity of active region (AR) NOAA 12673 during a ten-hour time interval centered around a preceding X2.2 flare (SOL2017-09-06T08:57) and also including an eruptive X9.3 flare that occurred three hours later (SOL2017-09-06T11:53). In particular, we aim for a reliable estimate of the normalized self-helicity of the current-carrying magnetic field, the so-called helicity ratio, |HJ|/|H𝒱|, a promising candidate to quantity the eruptive potential of solar ARs. Methods. Using Solar Dynamics Observatory Helioseismic and Magnetic Imager vector magnetic field data as an input, we employ nonlinear force-free (NLFF) coronal magnetic field models using an optimization approach. The corresponding relative helicity, and related quantities, are computed using a finite-volume method. From multiple time series of NLFF models based on different choices of free model parameters, we are able to assess the spread of |HJ|/|H𝒱|, and to estimate its uncertainty. Results. In comparison to earlier works, which identified the non-solenoidal contribution to the total magnetic energy, Ediv/E, as selection criterion regarding the required solenoidal quality of magnetic field models for subsequent relative helicity analysis, we propose to use in addition the non-solenoidal contribution to the free magnetic energy, |Emix|/EJ, s. As a recipe for a reliable estimate of the relative magnetic helicity (and related quantities), we recommend to employ multiple NLFF models based on different combinations of free model parameters, to retain only those that exhibit smallest values of both Ediv/E and |Emix|/EJ, s at a certain time instant, to subsequently compute mean estimates, and to use the spread of the individually contributing values as an indication for the uncertainty.