Magnetic reconnection plays a crucial role in the energy release process for different kinds of solar eruptions and activities. The rapid solar eruption requires a fast reconnection model. Plasmoid instability in the reconnecting current sheets is one of the most acceptable fast reconnection mechanisms for explaining the explosive events in the magnetohydrodynamics (MHD) scale, which is also a potential bridge between the macroscopic MHD reconnection process and microscale dissipations. Plenty of high-resolution observations indicate that the plasmoid-like structures exist in the high-temperature solar corona, but such evidences are very rare in the lower solar atmosphere with partially ionized plasmas. Utilizing joint observations from the Goode Solar Telescope and the Solar Dynamics Observatory, we discovered a small-scale eruptive phenomenon in NOAA Active Region 13085, characterized by clear reconnection cusp structures, supported by nonlinear force-free field extrapolation results. The plasmoid-like structures with a size of about 150 km were observed to be ejected downward from the current sheet at a maximum velocity of 24 km s⁻¹ in the Hα line wing images, followed by enhanced emissions at around the postflare loop region in multiple wavelengths. Our 2.5D high-resolution MHD simulations further reproduced such a phenomenon and revealed reconnection fine structures. These results provide comprehensive evidences for the plasmoid-mediated reconnection in partially ionized plasmas, and suggest a unified reconnection model for solar flares with different length scales from the lower chromosphere to the corona.

中文翻译：

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部分电离低太阳大气中小规模耀斑期间等离子体介导的磁重联的证据

磁重联在各种太阳喷发和活动的能量释放过程中起着至关重要的作用。太阳的快速喷发需要快速重联模型。重联电流片中的等离子体不稳定性是解释磁流体动力学（MHD）尺度爆炸事件最可接受的快速重联机制之一，也是宏观MHD重联过程和微观尺度耗散之间的潜在桥梁。大量高分辨率观测表明，高温日冕中存在类等离子体结构，但在具有部分电离等离子体的太阳低层大气中，这种证据非常罕见。利用古德太阳望远镜和太阳动力学观测站的联合观测，我们在 NOAA 活动区 13085 发现了小规模喷发现象，其特征是清晰的重联尖点结构，并得到非线性无力场外推结果的支持。观察到尺寸约150 km的类等离子体结构在H中以24 km s ^{-1的最大速度从电流片向下喷射。}α线翼图像，然后是后耀斑环路区域周围多个波长的增强发射。我们的 2.5D 高分辨率 MHD 模拟进一步再现了这种现象并揭示了重联精细结构。这些结果为部分电离等离子体中等离子体介导的重联提供了全面的证据，并提出了从色球层到日冕不同长度尺度的太阳耀斑的统一重联模型。