Bipolar Reversal in the Off-Diagonal Ion Pressure Term in Collisionless Magnetic Reconnection

IF 2.6 2区 地球科学 Q2 ASTRONOMY & ASTROPHYSICS
Kailai Wang, Lei Dai, Shan Wang, Yong Ren, Minghui Zhu, Chi Wang, Benoit Lavraud, C. Philippe Escoubet, James L. Burch
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Abstract

Magnetic reconnection is a fundamental process that converts magnetic energy into particle energy, with wide applications in space plasmas. A key manifestation of this energy conversion is the acceleration of fast ion outflows. However, ion processes and their associated signatures in energy conversion remains only partially understood in collisionless magnetic reconnection. In this study, we utilize statistical analyses of in-situ observations and particle-in-cell (PIC) simulations to identify a distinct signature in the off-diagonal component of the ion pressure tensor. This signature displays a bipolar reversal that correlates with ion outflows across the reconnection X-line. The bipolar signal originates from distorted ion velocity distributions during acceleration. These signals are confirmed by statistical in-situ evidence for the first time and captured by PIC simulations. PIC simulations further indicate the peak of the off-diagonal ion pressure is near the magnetic pileup region associated with the ion outflow. Trajectories of ions in the distorted velocity distributions are traced within the PIC simulations. Ions in the distorted distributions undergo partial cyclotron motion around the reconnected magnetic field (Bz) and acceleration by the reconnection electric fields. The observation of bipolar reversal in the off-diagonal ion pressure term indicate its spatial gradient, which could contribute to supporting ion-scale reconnection electric fields. These findings provide new insights into the fundamental features of energy conversion in collisionless magnetic reconnection.

无碰撞磁重联中非对角线离子压力项的双极反转
磁重联是将磁能转化为粒子能的基本过程,在空间等离子体中有着广泛的应用。这种能量转换的一个关键表现是快速离子流出的加速。然而,在无碰撞磁重联中,能量转换中的离子过程及其相关特征仅被部分理解。在这项研究中,我们利用原位观测和粒子池(PIC)模拟的统计分析来识别离子压力张量的非对角线分量的明显特征。这个特征显示了一个双极反转,它与离子流出有关,穿过重连的x线。双极信号源于加速过程中离子速度分布的畸变。这些信号首次被现场统计证据证实,并被PIC模拟捕获。PIC模拟进一步表明,非对角线离子压力峰值位于与离子流出相关的磁堆积区附近。在PIC模拟中跟踪了扭曲速度分布中的离子轨迹。畸变分布中的离子在重联磁场(Bz)周围进行部分回旋运动,并在重联电场的作用下加速。在非对角线离子压力项中观察到的双极性反转表明了其空间梯度,这有助于支持离子尺度的重联电场。这些发现对无碰撞磁重联中能量转换的基本特征提供了新的见解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Geophysical Research: Space Physics
Journal of Geophysical Research: Space Physics Earth and Planetary Sciences-Geophysics
CiteScore
5.30
自引率
35.70%
发文量
570
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