Alfvén wings in the lunar wake: The role of pressure gradients
Alfvén wings in the lunar wake: The role of pressure gradients
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DOI：
10.1002/2016ja022360
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发表时间：
2016-11
期刊：
影响因子：
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通讯作者：
H. Zhang;K. Khurana;M. Kivelson;S. Fatemi;M. Holmström;V. Angelopoulos;Y. Jia;W. Wan;L. Liu;Y. Chen;H. Le;Q. Shi;W. L. Liu
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文献类型：
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作者：
H. Zhang;K. Khurana;M. Kivelson;S. Fatemi;M. Holmström;V. Angelopoulos;Y. Jia;W. Wan;L. Liu;Y. Chen;H. Le;Q. Shi;W. L. Liu
在流动的等离子体中，强传导或磁化的障碍物会产生被称为阿尔芬翼的结构，它协调障碍物和等离子体之间的动量转移。不导电的障碍物，如无空气的行星体，可以产生这样的结构，然而，到目前为止，这种结构只在亚阿尔夫涅克地区才能看到。对两颗Artemis卫星同时进行的测量进行了一项新的统计分析，其中一颗在月球上游的太阳风中，另一颗在下游尾迹中，并将数据与相互作用的三维混合模型的结果进行了比较，结果表明，月球下游的扰动等离子体在超级AlfvéNic太阳风中产生了Alfvén翼。在尾流区，磁力线向月球凸起，等离子体流明显受到扰动。我们使用模拟来表明，所观察到的场的某些弯曲是由场向电流引起的。因此，尾迹中的扰动是由压缩扰动和Alfvénic扰动共同引起的。由于太阳风的超Alfvénic背景流，两个Alfvén翼向后折叠，形成一个小的交叉角。在尾迹中形成阿尔芬翼的电流是由等离子体流减速和等离子体压力梯度共同驱动的，等离子体压力梯度从月球下游区域顺着尾迹向下正向移动。这种由尾流中的压力梯度和由此产生的等离子体减速引起的阿尔芬翼结构，应该存在于超阿尔夫尼克等离子体流中任何非导电体的下游。
Strongly conducting or magnetized obstacles in a flowing plasma generate structures called Alfvén wings, which mediate momentum transfer between the obstacle and the plasma. Nonconducting obstacles such as airless planetary bodies can generate such structures, which, however, have so far been seen only in sub‐Alfvénic regime. A novel statistical analysis of simultaneous measurements made by two ARTEMIS satellites, one in the solar wind upstream of the Moon and one in the downstream wake, and comparison of the data with results of a three‐dimensional hybrid model of the interaction reveal that the perturbed plasma downstream of the Moon generates Alfvén wings in super‐Alfvénic solar wind. In the wake region, magnetic field lines bulge toward the Moon and the plasma flows are significantly perturbed. We use the simulation to show that some of the observed bends of the field result from field‐aligned currents. The perturbations in the wake thus arise from a combination of compressional and Alfvénic perturbations. Because of the super‐Alfvénic background flow of the solar wind, the two Alfvén wings fold back to form a small intersection angle. The currents that form the Alfvén wing in the wake are driven by both plasma flow deceleration and a gradient of plasma pressure, positive down the wake from the region just downstream of the Moon. Such Alfvén wing structures, caused by pressure gradients in the wake and the resulting plasma slowdown, should exist downstream of any nonconducting body in a super‐Alfvénic plasma flow.