DOI: 10.1002/2017JA024901
Scopus记录号: 2-s2.0-85040722560
论文题名: On the Acceleration and Anisotropy of Ions Within Magnetotail Dipolarizing Flux Bundles
作者: Zhou X.-Z. ; Runov A. ; Angelopoulos V. ; Artemyev A.V. ; Birn J.
刊名: Journal of Geophysical Research: Space Physics
ISSN: 21699380
出版年: 2018
卷: 123, 期: 1 起始页码: 429
结束页码: 442
语种: 英语
英文关键词: dipolarization front
; dipolarizing flux bundle
; ion anisotropy
; ion reflection
; nonadiabatic acceleration
; stochastic orbit
英文摘要: Dipolarizing flux bundles (DFBs), earthward propagating structures with enhanced northward magnetic field Bz, are usually believed to carry a distinctly different plasma population from that in the ambient magnetotail plasma sheet. The ion distribution functions within the DFB, however, have been recently found to be largely controlled by the ion adiabaticity parameter κ in the ambient plasma sheet outside the DFB. According to these observations, the ambient κ values of 2–3 usually correspond to a strong perpendicular anisotropy of suprathermal ions within the DFB, whereas for lower κ values the DFB ions become more isotropic. Here we utilize a simple, test particle model to explore the nature of the anisotropy and its dependence on the ambient κ values. We find that the anisotropy originates from successive ion reflections and reentries to the DFB, during which the ions are consecutively accelerated in the perpendicular direction by the DFB-associated electric field. This consecutive acceleration may be interrupted, however, when magnetic field lines are highly curved in the ambient plasma sheet. In this case, the ion trajectories become stochastic outside the DFB, which makes the reflected ions less likely to return to the DFB for another cycle of acceleration; as a consequence, the perpendicular ion anisotropy does not appear. Given that the DFB ions are a free energy source for instabilities when they are injected toward Earth, our simple model (that reproduces most observational features on the anisotropic DFB ion distributions) may shed new lights on the coupling process between magnetotail and inner magnetosphere. ©2018. American Geophysical Union. All Rights Reserved. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/114873
Appears in Collections: 气候减缓与适应
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作者单位: School of Earth and Space Sciences, Peking University, Beijing, China; Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, United States; Space Science Institute, Boulder, CO, United States
Recommended Citation:
Zhou X.-Z.,Runov A.,Angelopoulos V.,et al. On the Acceleration and Anisotropy of Ions Within Magnetotail Dipolarizing Flux Bundles[J]. Journal of Geophysical Research: Space Physics,2018-01-01,123(1)