A Steady-State Picture of Solar Wind Acceleration and Charge State Composition Derived from a Global Wave-Driven MHD Model
Rona Oran, Enrico Landi, Bart van der Holst, Susan T. Lepri, Alberto M. Vásquez, Federico. A. Nuevo, Richard Frazin, Ward B. Manchester, Igor V. Sokolov, Tamas I. Gombosi
与快速流相比，在慢速（$<$ 400 km s $^{-1}$）太阳风流中发现的更高的电荷状态支持了慢风起源于封闭的日冕环并通过重连间歇性释放的假设。在这里，我们研究是否一个高度电离的慢风也可以形成沿稳定和开放的磁场线。我们使用AWSoM模型的稳态太阳大气，一个全球磁流体动力学模型驱动的Alfv{é}n波，并应用电离代码来计算电荷状态的演变沿建模的开放场线。这构成了覆盖现实磁场中所有纬度的第一电荷状态计算。的比率$O^{+7}/O^{+6}$和$C^{+6}/C^{+5}$相比，在现场观测，并被发现是较高的慢风，观察到的，但是，他们在两种风类型的预测。建模的离子分数的S，Si和Fe被用来计算线的视线强度，这是比较的EIS观测以上的冕洞。该协议是部分的，并表明所有的电离率都低于预测。假设超热电子的存在，改善了与EIS和ESTA观测的一致性;重要的是，保持了慢风中较高电离的趋势。结果表明，可能存在一种稳定且高度电离的慢风子类。进一步的分析表明，它起源于日冕洞边界（CHB），其中模拟的电子密度和温度高于洞内，导致更快的电离。CHB的这种性质是全球性的，并且得到EUV层析成像的观测支持。
英文摘要：
The higher charge states found in slow ($<$400km s$^{-1}$) solar wind streams compared to fast streams have supported the hypothesis that the slow wind originates in closed coronal loops, and released intermittently through reconnection. Here we examine whether a highly ionized slow wind can also form along steady and open magnetic field lines. We model the steady-state solar atmosphere using AWSoM, a global magnetohydrodynamic model driven by Alfv{é}n waves, and apply an ionization code to calculate the charge state evolution along modeled open field lines. This constitutes the first charge states calculation covering all latitudes in a realistic magnetic field. The ratios $O^{+7}/O^{+6}$ and $C^{+6}/C^{+5}$ are compared to in-situ Ulysses observations, and are found to be higher in the slow wind, as observed; however, they are under-predicted in both wind types. The modeled ion fractions of S, Si, and Fe are used to calculate line-of-sight intensities, which are compared to EIS observations above a coronal hole. The agreement is partial, and suggests that all ionization rates are under-predicted. Assuming the presence of suprathermal electrons improved the agreement with both EIS and Ulysses observations; importantly, the trend of higher ionization in the slow wind was maintained. The results suggest there can be a sub-class of slow wind that is steady and highly ionized. Further analysis shows it originates from coronal hole boundaries (CHB), where the modeled electron density and temperature are higher than inside the hole, leading to faster ionization. This property of CHBs is global, and observationally supported by EUV tomography.
Time-evolving coronal modelling of the solar maximum around the solar storms in May 2024 by COCONUT
KU Leuven（荷语鲁汶大学）；University of Maria Curie-Skłodowska（玛丽亚·居里-斯可夫多夫斯卡大学）；Von Karman Institute For Fluid Dynamics（冯·卡门流体力学研究所）；University of Oslo（奥斯陆大学）
Modeling the CO outflow in DG Tau B: Swept-up shells versus perturbed MHD disk wind
外流的起源及其对盘演化和行星形成的确切影响仍然是关键的悬而未决的问题。DG Tau B是一颗I类原恒星，伴随着旋转的锥形CO外流和结构盘。因此，它是研究这些问题的理想对象。我们的目标是描述DG Tau B外流的形态和运动学特征，以阐明其起源和对磁盘的潜在影响。我们的分析基于阿塔卡马大型毫米波阵列（ALMA）12 CO（2-1）以20 au角分辨率对DG Tau B的观测。我们表征三种不同类型的子结构在这个流出（拱，手指，尖）与明显的加速度。具有哈勃定律的风力驱动的壳模型无法解释这些子结构。相反，锥形流的形态学和运动学都可以用稳定的锥形磁流体动力（MHD）盘风来解释，其足点半径r 0 = 0.7-3.4 au，小磁水平臂参数λ < 1.6）和准周期性亮度增强。这些可能是由喷气弓冲击，源轨道运动所造成的25兆焦耳的同伴在50天文单位，或磁盘密度扰动通过风发射区吸积的影响。大的CO风质量通量（吸积率的四倍到中心恒星）也可以解释，如果MHD磁盘风删除了大部分的角动量所需的稳定磁盘吸积。我们的研究结果提供了最有力的证据，到目前为止，存在大量的MHD盘风在I类源与残留的下落，他们认为，初始阶段的行星形成发生在一个高度动态的环境。
