On the Extrapolation of Magnetohydrostatic Equilibria on the Sun
On the Extrapolation of Magnetohydrostatic Equilibria on the Sun
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DOI：
10.3847/1538-4357/aadf7f
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发表时间：
2018-09
期刊：
影响因子：
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通讯作者：
Xiaoshuai Zhu;T. Wiegelmann
中科院分区：
文献类型：
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作者：
Xiaoshuai Zhu;T. Wiegelmann
模拟太阳光球层和日冕之间的界面区域是具有挑战性的，因为磁场力和等离子体力的相对重要性变化了几个数量级。虽然日冕可以用无力假设来模拟，但我们需要在磁流体静力学（MHS）模型中考虑光球层和色球层中的等离子体力（压力梯度和重力）。我们用最优化原理求解MHS方程，并以矢量磁图作为边界条件。通过用两个新的基本变量替换正压和密度来确保它们。在优化过程中，洛伦兹力被用来更新底部边界上的等离子体压力，这使得新的外推工作，即使没有压力测量的光球。我们的代码进行了测试，使用线性MHS模型作为参考。从详细的分析，我们发现，新开发的MHS外推恢复参考模型在高精度。然而，MHS外推法在数值上比非线性无力场外推法更昂贵，因此应将其应用限制在等离子体力变得重要的区域，例如，在光球层上方约2微米的一层中。
Modeling the interface region between the solar photosphere and corona is challenging because the relative importance of magnetic and plasma forces change by several orders of magnitude. While the solar corona can be modeled by the force-free assumption, we need to take plasma forces into account (pressure gradient and gravity) in photosphere and chromosphere, here within the magnetohydrostatic (MHS) model. We solve the MHS equations with the help of an optimization principle and use vector magnetogram as the boundary condition. Positive pressure and density are ensured by replacing them with two new basic variables. The Lorentz force during optimization is used to update the plasma pressure on the bottom boundary, which makes the new extrapolation work even without pressure measurements on the photosphere. Our code is tested using a linear MHS model as reference. From the detailed analyses, we find that the newly developed MHS extrapolation recovers the reference model at high accuracy. The MHS extrapolation is, however, numerically more expensive than the nonlinear force-free field extrapolation and consequently one should limit their application to regions where plasma forces become important, e.g., in a layer of about 2 Mm above the photosphere.