[论文解读] Defining the Middle Corona

Matthew J. West, Daniel B. Seaton+32 more|Discovery Research Portal (University of Dundee)|Aug 9, 2022

Solar and Space Plasma Dynamics被引用 6

一句话总结

本文基于磁场拓扑结构、等离子体β值和流动动力学的物理转变，确立了日球层中间日冕的共识定义，即从约1.5至6个太阳半径（R⊙）的区域。该定义统一了观测与模拟视角，明确了太阳风加速与日冕加热线研究中一个长期界定不清的关键区域。

ABSTRACT

The middle corona, the region roughly spanning heliocentric altitudes from $1.5$ to $6\,R_\odot$, encompasses almost all of the influential physical transitions and processes that govern the behavior of coronal outflow into the heliosphere. Eruptions that could disrupt the near-Earth environment propagate through it. Importantly, it modulates inflow from above that can drive dynamic changes at lower heights in the inner corona. Consequently, this region is essential for comprehensively connecting the corona to the heliosphere and for developing corresponding global models. Nonetheless, because it is challenging to observe, the middle corona has been poorly studied by major solar remote sensing missions and instruments, extending back to the Solar and Heliospheric Observatory (SoHO) era. Thanks to recent advances in instrumentation, observational processing techniques, and a realization of the importance of the region, interest in the middle corona has increased. Although the region cannot be intrinsically separated from other regions of the solar atmosphere, there has emerged a need to define the region in terms of its location and extension in the solar atmosphere, its composition, the physical transitions it covers, and the underlying physics believed to be encapsulated by the region. This paper aims to define the middle corona and give an overview of the processes that occur there.

研究动机与目标

• 解决长期以来关于中间日冕边界存在的模糊性，该区域对太阳风加速与日冕加热研究至关重要。
• 基于物理转变与历史观测背景，建立太阳物理界对中间日冕的共识定义。
• 通过明确该区域在太阳-日球系统中的作用，特别是与开放/闭合磁力线及等离子体β值变化的关系，支持未来研究。
• 通过定义共享的观测与模拟框架，促进多仪器、多波段的协同研究。
• 通过标准化区域定义，推动跨学科合作，使复杂日冕动力学的研究更加聚焦。

提出的方法

• 通过由社区主导的工作坊与在线讨论，整合来自太阳物理学、光谱学、射电天文学与模拟研究的50多位研究人员的输入。
• 评估来自日冕成像、光谱学、射电爆发与原位测量的观测证据，以识别关键的物理转变。
• 将内边界（约1.5 R⊙）定义为闭合磁力线结构占主导地位且流体静力平衡开始失效的高度。
• 将外边界（约6 R⊙）定义为等离子体流动完全变为径向且日冕结构过渡至开放磁力线喷流区的区域。
• 利用源面模型（如PFSS）以及Sheeley Blobs的观测结果，将外边界锚定在3–6 R⊙范围。
• 整合多个任务（如Ulysses、SOHO、STEREO、Parker Solar Probe）与仪器（如SECCHI、SDO、Solar Orbiter）的数据，以验证该区域的边界。

Figure 1. : A SWAP and LASCO composite image highlighting the middle corona, and the physical transitions that extend through the region. The image also highlights the observational gap between EUV observations of the inner corona and visible-light observations of the outer corona, currently experie

实验结果

研究问题

• RQ1 哪些物理转变定义了中间日冕？它们如何将其与内日冕和外日冕区分开？
• RQ2 太阳风加速区域的确切起始位置在哪里？这与磁场拓扑结构和等离子体β值有何关联？
• RQ3 来自射电、极紫外与光谱数据的观测约束如何界定中间日冕的边界？
• RQ4 磁重联与密度不均匀性（如Sheeley Blobs）在定义中间日冕外边缘中起什么作用？
• RQ5 标准化的中间日冕定义如何提升建模、观测与太阳物理界的合作水平？

主要发现

• 中间日冕定义为从太阳圆面中心起算，约1.5至6个太阳半径（R⊙）的区域。
• 内边界（约1.5 R⊙）对应于闭合磁力线结构占主导地位且流体静力平衡开始失效的高度。
• 外边界（约6 R⊙）与完全径向流动的出现以及日冕结构中超径向膨胀的消失相一致。
• 来自日冕洞、日冕亮带与Sheeley Blobs的观测证据支持3–6 R⊙范围作为中间日冕的外限。
• 该区域包含了关键的物理转变，包括闭合磁场向开放磁场的过渡，以及宁静太阳区域等离子体β值的上升。
• 共识定义基于物理机制与历史观测实践，为未来研究提供了统一的框架。

Figure 2. : ( a ) Summary of past, present, planned, and proposed middle corona observatories. The type of observation is indicated in the brackets , with key to symbolic abbreviations in upper right of the figure. Color corresponds to the wavelength regime of the observation, X-ray (Gold), EUV/UV (