弱随机磁重联的数值研究
Numerical Studies of Weakly Stochastic Magnetic Reconnection
摘要：
我们利用三维数值模拟研究了湍流对磁重联的影响。这是第一次尝试测试Lazarian & Vishniac（1999）提出的快速磁重联模型，该模型假设电流片附近存在弱的小尺度磁场结构。这会通过减少重联流的横向尺度和允许许多独立的通量重联事件同时发生来影响重联率。我们进行了一些模拟测试的依赖关系的重连速度，定义为流入速度的比率，阿尔芬速度，湍流功率，注入规模和电阻率。结果表明，湍流显著影响了扩散区附近的磁场拓扑结构，并增加了流出区的厚度。我们证实了Lazarian & Vishniac模型的预测。特别地，我们报告了重联速度与~ V^2成正比的增长，其中V是注入尺度下的速度幅度。它取决于注入比例l为~（l/L）^（2/3），其中L是系统的大小，这稍微快一些，但仍然与理论预期大致一致。我们还表明，对于三维重联欧姆电阻率是重要的局部重联事件，并在湍流的存在下，全球重联率并不依赖于它。
英文摘要：
We study the effects of turbulence on magnetic reconnection using three-dimensional numerical simulations. This is the first attempt to test a model of fast magnetic reconnection proposed by Lazarian & Vishniac (1999), which assumes the presence of weak, small-scale magnetic field structure near the current sheet. This affects the rate of reconnection by reducing the transverse scale for reconnection flows and by allowing many independent flux reconnection events to occur simultaneously. We performed a number of simulations to test the dependencies of the reconnection speed, defined as the ratio of the inflow velocity to the Alfven speed, on the turbulence power, the injection scale and resistivity. Our results show that turbulence significantly affects the topology of magnetic field near the diffusion region and increases the thickness of the outflow region. We confirm the predictions of the Lazarian & Vishniac model. In particular, we report the growth of the reconnection speed proportional to ~ V^2, where V is the amplitude of velocity at the injection scale. It depends on the injection scale l as ~ (l/L)^(2/3), where L is the size of the system, which is somewhat faster but still roughly consistent with the theoretical expectations. We also show that for 3D reconnection the Ohmic resistivity is important in the local reconnection events only, and the global reconnection rate in the presence of turbulence does not depend on it.
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