Zhang L Q, Wang Chi, Baumjohann W, Wang R S, Wang J Y, Burch James L, Khotyaintsev Yu V
State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, 100080, China.
Space Research Institute, Austrian Academy of Sciences, 8042, Graz, Austria.
Sci Rep. 2023 Nov 6;13(1):19201. doi: 10.1038/s41598-023-45867-w.
Turbulence is a ubiquitous phenomenon in neutral and conductive fluids. According to classical theory, turbulence is a rotating flow containing vortices of different scales. Eddies play a fundamental role in the nonlinear cascade of kinetic energy at different scales in turbulent flow. In conductive fluids, the Alfvénic/kinetic Alfvénic wave (AW/KAW) is the new "cell" of magnetohydrodynamic (MHD) turbulence (frozen-in condition). Wave energy, which has equal kinetic and magnetic energy, is redistributed among multiple-scale Fourier modes and transferred from the large MHD scale to the small kinetic scale through the collision of counter-propagating Alfvénic wave packages propagating along the magnetic field line. Fluid-like eddy-dominant plasma flow turbulence has never been found in space since the launch of the first satellite in 1957. In this paper, we report the first observation of eddy-dominant turbulence within magnetic reconnection-generated fast flow in the Earth's tail plasma sheet by the Magnetospheric Multiscale Spacecraft (MMS). In eddy-dominant turbulent reconnection jet, ions dominate the flow field while electrons dominate current and magnetic fluctuations. Our findings shed new light on the nonlinear kinetic and magnetic energy cascade in MHD turbulence.
湍流是中性流体和导电流体中普遍存在的现象。根据经典理论，湍流是一种包含不同尺度涡旋的旋转流。涡旋在湍流中不同尺度动能的非线性级联中起着基础性作用。在导电流体中，阿尔文波/动力学阿尔文波（AW/KAW）是磁流体动力学（MHD）湍流（冻结条件）的新“单元”。具有相等动能和磁能的波动能量在多尺度傅里叶模式之间重新分布，并通过沿磁力线反向传播的阿尔文波包的碰撞，从大MHD尺度转移到小动能尺度。自1957年第一颗卫星发射以来，在太空中从未发现过类似流体的以涡旋为主的等离子体流湍流。在本文中，我们报告了磁层多尺度航天器（MMS）首次观测到地球尾等离子体片中磁重联产生的快速流中以涡旋为主的湍流。在以涡旋为主的湍流重联喷流中，离子主导流场，而电子主导电流和磁波动。我们的发现为MHD湍流中的非线性动能和磁能级联提供了新的线索。
