Combining magnetohydrostatic constraints with Stokes profiles inversions
Combining magnetohydrostatic constraints with Stokes profiles inversions
复制标题
将磁流体静力约束与斯托克斯剖面反演相结合
DOI：
10.1051/0004-6361/201936367
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发表时间：
2019
影响因子：
6.5
通讯作者：
Ruiz Cobo
中科院分区：
文献类型：
--
作者：
Borrero;Pastor Yabar;Rempel;Ruiz Cobo
当应用于分光偏振观测时，用于偏振辐射传输方程的上下文反演代码（即，Stokes矢量），可以用来推断温度T、视向速度vlos和磁场B随连续光深τc的变化。然而，它们并不直接提供气体压力P或密度ρ。为了获得这些参数，反演代码依赖于流体静力平衡（HE）的假设，除了状态方程（EOS）。不幸的是，HE的假设在磁力线上是相当不切实际的，导致Pg和ρ的估计是不可靠的。这是因为洛伦兹力等因素的作用被忽视了。不可靠的气体压力和密度也转化为从光学深度τ c到几何高度tz的不准确转换。目的我们旨在通过应用磁流体静力学（MHS）平衡代替HE来改进气体压力和密度的确定。方法我们发展了一种方法来求解MHS平衡下的动量方程（即，考虑到洛伦兹力）在三维中。该方法是基于一个泊松方程的迭代解。以太阳黑子三维磁流体动力学（MHD）模拟得到的气体压强Pg和密度ρ为基准，比较了采用不同真实度边界条件的HE平衡和MHS平衡的结果。采用边界条件，可以应用于实际观测，我们发现，他检索的气体压力和密度的误差小于一个数量级（相比MHD值），只有约47%的网格点在三维域。此外，推断的值在仅约23%的域中的MHD值的两个因子内。这意味着在确定z-τ c转换时会产生约160-200 km的误差（即， 威尔逊抑郁症）。另一方面，应用具有相似边界条件的MHS平衡，可以在84%的区域内以小于一个数量级的误差确定Pg和ρ。在超过55%的域中，推断值在2的因子内。在后一种情况下，z-τ c转换的精度为30 - 70 km。 不准确是由于在平等的部分偏离MHS平衡和边界conditions.ResultsCompared的不准确，我们的新方法，基于MHS平衡，显着提高了可靠性的密度，气体压力的测定，和几何高度tzand连续光学深度τc之间的转换。该方法可与偏振光辐射传输方程的反演结合使用，以确定太阳大气的热力学、运动学和磁参数。
ContextInversion codes for the polarized radiative transfer equation, when applied to spectropolarimetric observations (i.e., Stokes vector) in spectral lines, can be used to infer the temperatureT, line-of-sight velocityvlos, and magnetic fieldBas a function of the continuum optical-depthτc. However, they do not directly provide the gas pressurePgor densityρ. In order to obtain these latter parameters, inversion codes rely instead on the assumption of hydrostatic equilibrium (HE) in addition to the equation of state (EOS). Unfortunately, the assumption of HE is rather unrealistic across magnetic field lines, causing estimations ofPgandρto be unreliable. This is because the role of the Lorentz force, among other factors, is neglected. Unreliable gas pressure and density also translate into an inaccurate conversion from optical depthτcto geometrical heightz.AimsWe aim at improving the determination of the gas pressure and density via the application of magnetohydrostatic (MHS) equilibrium instead of HE.MethodsWe develop a method to solve the momentum equation under MHS equilibrium (i.e., taking the Lorentz force into account) in three dimensions. The method is based on the iterative solution of a Poisson-like equation. Considering the gas pressurePgand densityρfrom three-dimensional magnetohydrodynamic (MHD) simulations of sunspots as a benchmark, we compare the results from the application of HE and MHS equilibrium using boundary conditions with different degrees of realism. Employing boundary conditions that can be applied to actual observations, we find that HE retrieves the gas pressure and density with an error smaller than one order of magnitude (compared to the MHD values) in only about 47% of the grid points in the three-dimensional domain. Moreover, the inferred values are within a factor of two of the MHD values in only about 23% of the domain. This translates into an error of about 160 − 200 km in the determination of thez−τcconversion (i.e., Wilson depression). On the other hand, the application of MHS equilibrium with similar boundary conditions allows determination ofPgandρwith an error smaller than an order of magnitude in 84% of the domain. The inferred values are within a factor of two in more than 55% of the domain. In this latter case, thez−τcconversion is obtained with an accuracy of 30 − 70 km. Inaccuracies are due in equal part to deviations from MHS equilibrium and to inaccuracies in the boundary conditions.ResultsCompared to HE, our new method, based on MHS equilibrium, significantly improves the reliability in the determination of the density, gas pressure, and conversion between geometrical heightzand continuum optical depthτc. This method could be used in conjunction with the inversion of the radiative transfer equation for polarized light in order to determine the thermodynamic, kinematic, and magnetic parameters of the solar atmosphere.
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影响因子：
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作者：
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通讯作者：
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DOI：
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DOI：
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发表时间：
2018-09
期刊：
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影响因子：
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作者：
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影响因子：
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作者：
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