Magnetospheric Multiscale Observation of Kinetic Signatures in the Alfvén Vortex
Magnetospheric Multiscale Observation of Kinetic Signatures in the Alfvén Vortex
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DOI：
10.3847/2041-8213/aafe0d
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发表时间：
2019-01
期刊：
影响因子：
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通讯作者：
Tieyan Wang;O. Alexandrova;D. Perrone;M. Dunlop;M. Dunlop;Xiangcheng Dong;R. Bingham;Y. Khotyaintsev
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文献类型：
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作者：
Tieyan Wang;O. Alexandrova;D. Perrone;M. Dunlop;M. Dunlop;Xiangcheng Dong;R. Bingham;Y. Khotyaintsev
Alfvén涡是一种多尺度的非线性结构，对湍流的不稳定性有贡献。尽管以前的探索主要是关于阿尔文涡旋的空间特性（即，尺度、方向和运动），阿尔文涡旋内的等离子体特性是未知的。此外，等离子体涡旋和阿尔芬涡旋之间的联系仍然不清楚。基于磁层多尺度使命的高分辨率原位测量，我们首次报告了阿尔文涡旋内独特的等离子体特征。这个阿尔文涡旋被认为是一个半径为10个质子陀螺仪的2D（）准单极。它的磁涨落与速度涨落是反相关的，因此平行的电流密度和流动涡度是反对齐的。在涡流的不同部分（即，边缘，中间，中心），离子和电子温度被发现是完全不同的，并且它们表现为相反的趋势：离子温度变化与相关，而电子温度变化与相关。此外，温度各向异性以及非麦克斯韦动力学效应在涡旋内的峰值处表现出强烈的增强。观测和数值/理论结果之间的比较。此外，还讨论了与Alfvén涡有关的能量转换通道和压缩性。这些结果有助于理解弱碰撞空间等离子体中相干涡旋结构与决定湍流能量耗散的动力学过程之间的联系。
Alfvén vortex is a multiscale nonlinear structure that contributes to the intermittency of turbulence. Despite previous explorations mostly on the spatial properties of the Alfvén vortex (i.e., scale, orientation, and motion), the plasma characteristics within the Alfvén vortex are unknown. Moreover, the connection between the plasma energization and the Alfvén vortex still remains unclear. Based on high-resolution in situ measurements from the Magnetospheric Multiscale mission, we report for the first time distinctive plasma features within an Alfvén vortex. This Alfvén vortex is identified as being a 2D ( ) quasi-monopole with a radius of 10 proton gyroscales. Its magnetic fluctuations are anti-correlated with velocity fluctuations , thus the parallel current density and flow vorticity are anti-aligned. In different part of the vortex (i.e., edge, middle, center), the ion and electron temperatures are found to be quite different and they behave in the reverse trend: the ion temperature variations are correlated with , while the electron temperature variations are correlated with . Furthermore, the temperature anisotropies, together with the non-Maxwellian kinetic effects, exhibit strong enhancement at peaks of within the vortex. Comparison between observations and numerical/theoretical results are made. In addition, the energy-conversion channels and the compressibility associated with the Alfvén vortex are discussed. These results may help to understand the link between coherent vortex structures and the kinetic processes, which determines how turbulence energy dissipates in the weakly collisional space plasmas.