发表机构
Yunnan Observatories, Chinese Academy of Science; Yunnan Key Laboratory of Solar Physics and Space Science; University of Chinese Academy of Sciences; Dr. K. S. Krishnan Geomagnetic Research Laboratory, Indian Institute of Geomagnetism; School of Earth and Space Sciences, Peking University; State Key Laboratory of Solar Activity and Space Weather, National Space Science Center, Chinese Academy of Sciences（中国科学院云南天文台; 云南省太阳物理与空间科学重点实验室; 中国科学院大学; 印度地球磁学研究所K.S.克里希南地磁研究实验室; 北京大学地球与空间科学学院; 中国科学院国家空间科学中心太阳活动与空间天气国家重点实验室）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过2.5D MHD模拟发现，在低初始等离子体β的色球磁重联中，等离子体团内因辐射冷却自放大可形成类似热不稳定性的冷致密凝聚结构，而在高β下则不发生。
AI 中文摘要
我们进行了高分辨率2.5D单流体磁流体动力学（MHD）模拟，以探索色球磁重联过程中等离子体团内冷致密结构的形成。该模型考虑了氢和氦的电离度随温度的变化，从而改进了扩散率和粘性，并包含了充分的辐射冷却。数值结果表明，在初始等离子体-β较低（β0 = 0.05）的情况下，新形成的等离子体团中等离子体温度显著升高，可达数万开尔文。随后，等离子体的局部聚集和温度下降导致爆炸性更强的辐射冷却过程。辐射冷却在8000 K至20000 K的温度范围内达到峰值。共空间密度增强、显著的辐射冷却、更短的辐射冷却时间尺度以及明显的温度下降，支持了等离子体团内存在类似热不稳定性凝聚的观点。在不同色球高度的所有低β0案例中均识别出类似的冷致密结构，表明这种现象不仅限于单一色球层。相比之下，在初始等离子体-β较高（β0 = 0.5）的情况下，致密等离子体团内的最高温度仅为约8000 K。因此，辐射冷却从未进入爆炸性增长阶段，类似热不稳定性的凝聚也未发生。这些发现表明，在低β0条件下，一旦辐射损失变得自放大，色球重联中就可能发展出等离子体团俘获凝聚。
英文摘要
We perform high-resolution 2.5D single-fluid magnetohydrodynamic (MHD) simulations to explore the development of cool-dense structures within plasmoids during chromospheric magnetic reconnection. The model incorporates temperature-dependent ionization degrees of hydrogen and helium, resulting in improved diffusivities and viscosity, as well as adequate radiative cooling. The numerical results show that plasma is significantly hot with temperatures reaching several tens of thousands of Kelvin in newly developed plasmoids in the low initial plasma-$β$ cases, $β_0$ = 0.05. Later, the localized accumulation of plasma and decreasing temperature result in an explosive much stronger radiative cooling process. Radiative cooling peaks over the temperature range 8000 K$-$20,000 K. The co-spatial density enhancement, substantial radiative cooling, shorter radiative cooling timescales, and a significant temperature decrease support the existence of thermal-instability-like condensation within the plasmoids. Similar cool-dense structures are identified in all low-$β_0$ cases at different chromospheric altitudes, suggesting that this occurrence is not limited to a single chromospheric layer. In contrast, in the high initial plasma-$β$, $β_0$ = 0.5 case, the maximum temperature inside the dense plasmoids is only about 8000 K. Therefore, the radiative cooling has never entered into the explosive increasing stage and the thermal-instability-like condensation does not happen. These findings reveal that plasmoid-trapped condensation may develop in chromospheric reconnection once radiative losses become self-amplifying under low-$β_0$ conditions.
