Lazarian A, Eyink G, Vishniac E, Kowal G
Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706, USA
Department of Applied Mathematics and Statistics, The Johns Hopkins University, Baltimore, MD 21218, USA.
Philos Trans A Math Phys Eng Sci. 2015 May 13;373(2041). doi: 10.1098/rsta.2014.0144.
Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes happening in magnetized plasmas. In most astrophysical environments, the Reynolds numbers corresponding to plasma flows are large and therefore the transition to turbulence is inevitable. This turbulence, which can be pre-existing or driven by magnetic reconnection itself, must be taken into account for any theory of magnetic reconnection that attempts to describe the process in the aforementioned environments. This necessity is obvious as three-dimensional high-resolution numerical simulations show the transition to the turbulence state of initially laminar reconnecting magnetic fields. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (Lazarian & Vishniac 1999 Astrophys. J. 517, 700-718 (doi:10.1086/307233)) reconnection model. We present numerical evidence supporting the model and demonstrate that it is closely connected to the experimentally proven concept of Richardson dispersion/diffusion as well as to more recent advances in understanding of the Lagrangian dynamics of magnetized fluids. We point out that the generalized Ohm's law that accounts for turbulent motion predicts the subdominance of the microphysical plasma effects for reconnection for realistically turbulent media. We show that one of the most dramatic consequences of turbulence is the violation of the generally accepted notion of magnetic flux freezing. This notion is a cornerstone of most theories dealing with magnetized plasmas, and therefore its change induces fundamental shifts in accepted paradigms, for instance, turbulent reconnection entails reconnection diffusion process that is essential for understanding star formation. We argue that at sufficiently high Reynolds numbers the process of tearing reconnection should transfer to turbulent reconnection. We discuss flares that are predicted by turbulent reconnection and relate this process to solar flares and γ-ray bursts. With reference to experiments, we analyse solar observations in situ as measurements in the solar wind or heliospheric current sheet and show the correspondence of data with turbulent reconnection predictions. Finally, we discuss first-order Fermi acceleration of particles that is a natural consequence of the turbulent reconnection.
磁重联是一种磁场拓扑结构变化的过程，它是磁化等离子体中发生的最基本过程之一。在大多数天体物理环境中，与等离子体流对应的雷诺数很大，因此向湍流的转变是不可避免的。这种湍流可能是预先存在的，也可能是由磁重联本身驱动的，对于任何试图描述上述环境中该过程的磁重联理论来说，都必须将其考虑在内。这一必要性是显而易见的，因为三维高分辨率数值模拟显示了初始层流重联磁场向湍流状态的转变。我们讨论了湍流如何改变重联的观点，重点关注拉扎里安和维什尼亚克（Lazarian & Vishniac 1999 Astrophys. J. 517, 700 - 718 (doi:10.1086/307233)）的重联模型。我们给出了支持该模型的数值证据，并证明它与经过实验验证的理查森弥散/扩散概念以及对磁化流体拉格朗日动力学理解的最新进展密切相关。我们指出，考虑湍流运动的广义欧姆定律预测，对于实际湍流介质，微观物理等离子体效应在重联中占次要地位。我们表明，湍流最显著的后果之一是违反了普遍接受的磁通量冻结概念。这个概念是大多数处理磁化等离子体理论的基石，因此它的改变会导致公认范式的根本转变，例如，湍流重联需要重联扩散过程，这对于理解恒星形成至关重要。我们认为，在足够高的雷诺数下，撕裂重联过程应转变为湍流重联。我们讨论了由湍流重联预测的耀斑，并将此过程与太阳耀斑和伽马射线暴联系起来。参照实验，我们分析了太阳风或日球电流片中的原位太阳观测数据，并展示了数据与湍流重联预测的对应关系。最后，我们讨论了粒子的一阶费米加速，这是湍流重联的自然结果。
