Preprocessing of vector magnetograms for magnetohydrostatic extrapolations
Preprocessing of vector magnetograms for magnetohydrostatic extrapolations
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DOI：
10.1051/0004-6361/202039079
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发表时间：
2020-10
影响因子：
6.5
通讯作者：
Xiaoshuai Zhu;T. Wiegelmann;B. Inhester
中科院分区：
文献类型：
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作者：
Xiaoshuai Zhu;T. Wiegelmann;B. Inhester
上下文了解三维磁场以及色球层和过渡区的等离子体是很重要的。一种方法是基于磁流体静力学（MHS）状态的假设，从常规测量的光球矢量磁图中推断磁场和等离子体。然而，光球数据可能与MHS假设不一致。因此，我们必须研究MHS系统对光球磁场的限制。此外，在应用MHS外推法之前，应对数据进行相应的转换。目标。我们的目标是获得一组表面积分作为标准的MHS系统，并使用这组积分预处理的矢量磁图。方法.通过应用高斯定理并假设太阳上有一个孤立的活动区，我们将太阳体积中的磁能和磁力与光球上的表面积分联系起来。同样的方法被应用于获得光球磁场的限制作为MHS系统的必要标准。我们使用优化方法对数据进行预处理，以最大限度地减少与标准和测量值的偏差。结果通过将维里定理应用于活动区，我们发现用于计算无力场能量的边界积分通常低估了大活动区的磁能。我们还发现，MHS假设只要求净洛仑兹力的x，y分量和净扭矩的z分量为零。这些零分量是Aly的无力场判据的一部分。然而，净力和扭矩的其他分量可以是非零值。根据新的标准，我们对磁图进行了预处理，使其与MHS系统更加一致，同时接近原始数据。
Context. Understanding the 3D magnetic field as well as the plasma in the chromosphere and transition region is important. One way is to extrapolate the magnetic field and plasma from the routinely measured vector magnetogram on the photosphere based on the assumption of the magnetohydrostatic (MHS) state. However, photospheric data may be inconsistent with the MHS assumption. Therefore, we must study the restriction on the photospheric magnetic field, which is required by the MHS system. Moreover, the data should be transformed accordingly before MHS extrapolations can be applied. Aims. We aim to obtain a set of surface integrals as criteria for the MHS system and use this set of integrals to preprocess a vector magnetogram. Methods. By applying Gauss’ theorem and assuming an isolated active region on the Sun, we related the magnetic energy and forces in the volume to the surface integral on the photosphere. The same method was applied to obtain restrictions on the photospheric magnetic field as necessary criteria for a MHS system. We used an optimization method to preprocess the data to minimize the deviation from the criteria as well as the measured value. Results. By applying the virial theorem to the active region, we find the boundary integral that is used to compute the energy of a force-free field usually underestimates the magnetic energy of a large active region. We also find that the MHS assumption only requires the x-, y-component of net Lorentz force and the z-component of net torque to be zero. These zero components are part of Aly’s criteria for a force-free field. However, other components of net force and torque can be non-zero values. According to new criteria, we preprocess the magnetogram to make it more consistent with the MHS system and, at the same time close, to the original data.