Using a 2D Viscoresistive Reduced MagnetoHydroDynamic model, the magnetic island coalescence problem is studied in the presence of in-plane, parallel shear flows. Extending the analytical work of Waelbroeck et al. [Phys. Plasmas 14, 022302 (2007)] and Throumoulopoulos et al., [J. Phys. A 42, 335501 (2009)] in the sub-Alfvénic flow shear regime for Fadeev equilibrium, the super-Alfvénic regime is studied for the first time numerically. A wide range of values of shear flow amplitudes and shear scale lengths have been considered to understand the effect of sub-Alfvénic and super-Alfvénic flows on the coalescence instability and its nonlinear fate. We find that for flow shear length scales greater than the magnetic island size, the maximum reconnection rate decreases monotonically from sub-Alfvénic to super-Alfvénic flow speeds. For scale lengths smaller than the island size, the reconnection rate decreases up to a critical value $v_{0c}$, beyond which the shear flow is found to destabilize the islands. The value of $v_{0c}$ decreases with a decrease in the value of shear flow length scale. Interestingly, for our range of parameters, we find suppression of the Kelvin–Helmholtz instability in super-Alfvénic flows even when the shear scale length is smaller than the island width. Observation of velocity streamlines shows that the plasma circulation inside the islands has a stabilizing influence in strong shear flow cases. Plasma circulation is also found to be responsible for the decrease in upstream velocity, causing less pileup of magnetic flux on both sides of the reconnection sheet.

中文翻译：

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面内剪切流对磁岛聚结不稳定性的影响

使用 2D Viscoresistive Reduced MagnetoHydroDynamic 模型，研究了存在面内平行剪切流时的磁岛聚结问题。扩展 Waelbroeck等人的分析工作。[物理。等离子体14，022302（2007）]和Throumoulopoulos等。, [J. 物理。一个42, 335501 (2009)] 在 Fadeev 平衡的亚阿尔芬流体剪切状态中，首次对超阿尔芬流体进行了数值研究。剪切流振幅和剪切尺度长度的广泛值已被考虑用于了解亚阿尔芬和超阿尔芬流动对聚结不稳定性及其非线性命运的影响。我们发现，对于大于磁岛尺寸的流动剪切长度尺度，最大重联率从亚阿尔文流速到超阿尔文流速单调降低。对于小于岛大小的尺度长度，重连率下降到一个临界值$v_{0C}$，超过该值的剪切流会破坏岛屿的稳定性。的价值$v_{0C}$随剪切流长度尺度值的减小而减小。有趣的是，对于我们的参数范围，我们发现即使当剪切尺度长度小于岛宽度时，超阿尔文流中的开尔文-亥姆霍兹不稳定性也会受到抑制。速度流线的观察表明，岛内的等离子体环流在强剪切流情况下具有稳定影响。还发现等离子体循环是造成上游速度降低的原因，导致重新连接片两侧的磁通量堆积较少。