论文标题

霍尔磁水动力学中三维相干结构的演变

Evolution of three-dimensional coherent structures in Hall magnetohydrodynamics

论文作者

Bora, Kamlesh, Bhattacharyya, Ramit, Smolarkiewicz, Piotr K.

论文摘要

这项工作将计算模型Eulag-MHD扩展到包括Hall Magnetodrodnymics(HMHD)---探索以离子惯性长度尺度顺序进行快速磁重新连接的物理系统的重要性。示例包括太阳瞬变以及磁层,磁尾和 实验室等离子体。本文记录了在有单向正弦磁场启动的大厅强迫项的存在和不存在的情况下,两组不同的大型模拟的结果。基准测试代码时的HMHD模拟还强调了三维(3D)演化在其二维(2D)对应物上的复杂性。磁重新连接在HMHD中显着较早。重要的是,霍尔项产生的磁场打破了任何固有的对称性,最终使进化3D。所得的3D重新连接会产生磁通绳和磁通管。绳索和管子被投影在重新连接平面上,后来散落到次要岛屿上,最终结合起来,产生了X型中性点。这些发现与HMHD的理论和当代模拟一致,因此验证了我们对Eulag-MHD模型的扩展。第二组探讨了大厅强迫对剪切磁场的磁通绳的产生和升序的影响---一种新的场景,指导着理解冠状动脉瞬变。绳索通过中间复杂的结构演变,最终由于重新连接而在本地破裂。有趣的是,断裂发生在霍尔术语的存在下,表示更快的动力学,导致有利于重新连接的磁性拓扑。

The work extends the computational model EULAG-MHD to include Hall magnetohydrodynamics (HMHD)---important to explore physical systems undergoing fast magnetic reconnection at the order of the ion inertial length scale. Examples include solar transients along with reconnections in magnetosphere, magnetotail and laboratory plasmas. The paper documents the results of two distinct sets of implicit large-eddy simulations in the presence and absence of the Hall forcing term, initiated with an unidirectional sinusoidal magnetic field. The HMHD simulation while benchmarking the code also emphasizes the complexity of three dimensional (3D) evolution over its two dimensional (2D) counterpart. The magnetic reconnections onset significantly earlier in HMHD. Importantly, the magnetic field generated by the Hall term breaks any inherent symmetry, ultimately making the evolution 3D. The resulting 3D reconnections develop magnetic flux ropes and magnetic flux tubes. Projected on the reconnection plane, the ropes and tubes appear as magnetic islands, which later break into secondary islands, and finally coalesce to generate an X-type neutral point. These findings are in agreement with the theory and contemporary simulations of HMHD, and thus verify our extension of the EULAG-MHD model. The second set explores the influence of the Hall forcing on generation and ascend of a magnetic flux rope from sheared magnetic arcades---a novel scenario instructive in understanding the coronal transients. The rope evolves through intermediate complex structures, ultimately breaking locally because of reconnections. Interestingly, the breakage occurs earlier in the presence of the Hall term, signifying faster dynamics leading to magnetic topology favorable for reconnections.

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