Using Transverse Waves to Probe the Plasma Conditions at the Base of the Solar Wind
Using Transverse Waves to Probe the Plasma Conditions at the Base of the Solar Wind
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DOI：
10.3847/1538-4357/ab7c59
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发表时间：
2020-05
期刊：
影响因子：
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通讯作者：
M. Weberg;R. Morton;J. McLaughlin
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文献类型：
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作者：
M. Weberg;R. Morton;J. McLaughlin
长期以来，人们一直认为磁流体动力（MHD）波可能提供加热日冕和加速太阳风所需的大部分能量。根据局部等离子体的特性，MHD 波模式可能表现为各种不可压缩的横波。局部磁场和粒子密度影响这些波的特性（例如振幅），因此横波的直接测量提供了一种间接探测局部等离子体条件的机制。我们提出了第一个太阳日冕局部区域磁震学的统计方法，分析了 2011 年 5 月 23 日南极日冕洞上方的横波。利用自动化方法检查 4 小时的 EUV 成像数据，以研究波如何随着穿过低日冕的高度（即高度）而演化。在 15 毫米到 35 毫米的高度之间，我们发现测量的波周期近似恒定，并且观察到的位移和速度幅度以与无阻尼波一致的速率增加。这使我们能够在不使用光谱数据的情况下得出相关日冕洞环境的相对密度剖面。此外，我们的结果表明，在肢体上方 5 至 15 Mm 之间，相对密度大于一维静水力模型的预期值，并表明过渡区域范围更大，密度逐渐变化。这对于从光球层到日冕及其他区域的波传播的自洽模型具有重要意义。
It has long been suggested that magnetohydrodynamic (MHD) waves may supply a significant proportion of the energy required to heat the corona and accelerate the solar wind. Depending on the properties of the local plasma, MHD wave modes may exhibit themselves as a variety of incompressible, transverse waves. The local magnetic field and particle density influence the properties of these waves (e.g., amplitude), thus direct measurements of transverse waves provide a mechanism to indirectly probe the local plasma conditions. We present the first statistical approach to magnetoseismology of a localized region of the solar corona, analyzing transverse waves above the south polar coronal hole on 2011 May 23. Automated methods are utilized to examine 4 hr of EUV imaging data to study how the waves evolve as a function of height (i.e., altitude) through the low corona. Between heights of 15 and 35 Mm, we find that the measured wave periods are approximately constant, and that observed displacement and velocity amplitudes increase at rates that are consistent with undamped waves. This enables us to derive a relative density profile for the coronal hole environment in question, without the use of spectroscopic data. Furthermore, our results indicate that between 5 and 15 Mm above the limb, the relative density is larger than that expected from 1D hydrostatic models, and signals a more extended transition region with a gradual change in density. This has implications for self-consistent models of wave propagation from the photosphere to the corona and beyond.