The scientific community employs complicated multiphysics simulations to understand the physics in Solar, Stellar, and Interstellar media. These must be tested against known solutions to ensure their validity. Several well-known tests exist, such as the Sod shock tube test. However, a test for nonlinear diffusivity is missing. This problem is highly relevant in the Solar atmosphere, where various events release energy that subsequently diffuses by Spitzer thermal conductivity. The aim is to derive an analytical solution for nonlinear diffusivity in 1D, 2D, and 3D, which allows for a nonzero background value. The solution will be used to design a test for numerical solvers and study Spitzer conductivity in the Solar atmosphere. There existed an ideal solution assuming zero background value. We perform an analytical first-order perturbation of this solution. The first-order solution is first tested against a dedicated nonlinear diffusion solver, whereupon it is used to benchmark the single- and multifluid radiative magnetohydrodynamics code Ebysus, used to study the Sun. The theory and numerical modeling are used to investigate the role of Spitzer conductivity in the transport of energy released in a nanoflare. The derived analytical solution models nonlinear diffusivity accurately within its region of validity and approximately beyond. Various numerical schemes in the Ebysus code have been found to model Spitzer conductivity correctly. The energy from a representative nanoflare has been found to diffuse 9 Mm within the first second of its lifetime due to Spitzer conductivity alone, strongly dependent on the electron density. The analytical first-order solution is a step forward in ensuring the physical validity of intricate simulations of the Sun. Additionally, since the derivation and argumentation are general, they can easily be followed to treat other nonlinear diffusion problems.
Investigating the propagation of small-scale flare energy in the lower and upper atmosphere of solar active region
Physical Research Laboratory（物理研究实验室）；Indian Institute of Technology Gandhinagar（甘地纳加尔印度理工学院）；University of Cambridge（剑桥大学）；University of Sheffield（谢菲尔德大学）；Eötvös Loránd University（罗兰大学）；Gyula Bay Zoltán Solar Observatory (GSO)（久拉·巴伊·佐尔坦太阳观测站）
A Magnetic Reconnection model for Hot Explosions in the Cool Atmosphere of the Sun
紫外线爆发和埃勒曼弹是在新兴通量区域的低太阳大气中观察到的短暂增亮。观测发现了同时空的EB和紫外暴，但其形成机制尚不清楚。这些事件中具有大温度跨度的多热成分挑战了我们对太阳低层大气中磁重联和加热机制的理解。我们研究了出现的和背景磁场之间的磁重联。初始等离子体参数基于C7大气模型。当光球层等离子体密度较大的电流片出现在距太阳表面$0.5$ Mm处时，等离子体团不稳定性开始出现。等离子体团相互碰撞并聚，使得不同密度和温度的等离子体在湍流重联区混杂在一起。因此，对应于UV发射的热等离子体和对应于来自其他波长的发射的较冷等离子体可以一起移动并且在大约相同的高度处发生。与此同时，热湍流结构基本上集中在$0.4$ Mm以上，而冷等离子体延伸到电流片底部的低得多的高度。这些现象与Chen et al. 2019，ApJL.合成的Si IV谱线轮廓与紫外暴中观测到的相似，谱线轮廓的增强翼可扩展到约$100$ km s $^{-1}$。不同分辨率的数值结果之间的差异是显着的，这表明，现实的磁扩散率是至关重要的，以揭示精细结构和现实的等离子体加热在这些重联事件。我们的结果还表明，在温度最低区附近的低色球层中，由双极扩散贡献的重联加热是无效的。
Energy and mass transport associated with impulsive spicular flows in solar coronal holes
Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Indian Institute of Astrophysics（印度天体物理研究所）；University of Sheffield（谢菲尔德大学）；Eötvös Loránd University（罗兰大学）
日冕和色球层之间的过渡区对于低层大气向日冕的质量和能量转移非常重要，因此，人们对这一区域进行了大量的紫外线和极紫外线观测研究。这些研究的一个主要结果是，在小于100 000 K的温度下，等离子体的量太大，与热导率的标准理论不兼容。然而，目前尚不清楚这种分歧是由于观测中的问题还是理论中的问题。我们解决这个问题，通过分析高空间和时间分辨率EUV观测的X1.6级耀斑采取的界面区域成像光谱仪（IRIS）和太阳动力学天文台/大气成像组件（SDO/AIA）。这些数据使我们能够从周围结构中分离出耀斑环的发射。我们比较了来自C II 1334.525 Ang的排放测量（EM），Si IV 1402.770 Ang过渡区谱线、Fe XXI 1354.066 Ang耀斑线和AIA 171 Ang日冕图像。我们发现，EM比率是不兼容的一个标准的传导为主的过渡区模型。此外，由于耀斑加热导致的EM幅度的大幅增加使得数据和理论之间的不一致极不可能是由于发射源的观测不确定性。我们的结论是，标准斯皮策伤害热导率必须是无效的，至少，耀斑环路。我们讨论的可能性，湍流抑制热传导可以解释我们的结果。
