David Vincent, Galtier Sébastien, Meyrand Romain
Laboratoire de Physique des Plasmas, École polytechnique, F-91128 Palaiseau Cedex, France.
Université Paris-Saclay, IPP, CNRS, Observatoire Paris-Meudon, France.
Phys Rev Lett. 2024 Feb 23;132(8):085201. doi: 10.1103/PhysRevLett.132.085201.
The breakdown of scale invariance in turbulent flows, known as multifractal scaling, is considered a cornerstone of turbulence. In solar wind turbulence, a monofractal behavior can be observed at electron scales, in contrast to larger scales where multifractality always prevails. Why scale invariance appears at electron scales is a challenging theoretical puzzle with important implications for understanding solar wind heating and acceleration. We investigate this long-standing problem using direct numerical simulations of three-dimensional electron reduced magnetohydrodynamics. Both weak and strong kinetic Alfvén waves turbulence regimes are studied in the balanced case. After recovering the expected theoretical predictions for the magnetic spectra, a higher-order multiscale statistical analysis is performed. This study reveals a striking difference between the two regimes, with the emergence of monofractality only in weak turbulence, whereas strong turbulence is multifractal. This result, combined with recent studies, shows the relevance of collisionless weak KAW turbulence to describe the solar wind at electron scales.
湍流中尺度不变性的破坏，即多重分形标度，被认为是湍流的基石。在太阳风湍流中，在电子尺度上可以观察到单分形行为，这与更大尺度上多重分形始终占主导的情况形成对比。尺度不变性为何出现在电子尺度上是一个具有挑战性的理论难题，对理解太阳风加热和加速具有重要意义。我们使用三维电子简化磁流体动力学的直接数值模拟来研究这个长期存在的问题。在平衡情况下研究了弱和强动力学阿尔文波湍流状态。在恢复了磁谱的预期理论预测之后，进行了高阶多尺度统计分析。这项研究揭示了两种状态之间的显著差异，单分形仅在弱湍流中出现，而强湍流是多重分形的。这一结果与最近的研究相结合，表明无碰撞弱动力学阿尔文波湍流对于描述电子尺度上的太阳风具有相关性。
