One-Step Local Acceleration Process of Ultra-Relativistic Electrons in the Center of the Outer Radiation Belt: Observations

IF 2.6 2区 地球科学 Q2 ASTRONOMY & ASTROPHYSICS
Deyu Guo, Dedong Wang, Yuri Shprits, Zheng Xiang, Binbin Ni, Anthony Saikin, Alexander Y. Drozdov, Matyas Szabo-Roberts, Jianhang Wang, Yangxizi Liu, Junhu Dong
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Abstract

Ultra-relativistic (>3 MeV) electrons are considered as a novel, separate population in the Earth's radiation belts since their loss and acceleration features are distinct from relativistic (∼MeV) electrons. The dominant acceleration mechanism of ultra-relativistic electrons remains a subject of ongoing debate. Some studies suggest that the acceleration mechanism of ultra-relativistic electrons is energy-dependent: local acceleration dominants the enhancement of ∼3–5 MeV electrons while two-step acceleration process leading by radial diffusion effects for ∼7 MeV electrons. However, a recent study (https://doi.org/10.1126/sciadv.abc0380) theoretically demonstrated that local acceleration could accelerate electrons up to >7 MeV directly under the extreme plasma depletion. In this study, we report four enhancement events of ultra-relativistic electrons that occurred in September and October 2017. Analysis of phase space density (PSD) radial profiles and contours demonstrate that local acceleration plays the dominant role in the enhancements of ∼7 MeV electrons in mid-September and mid-October, supported by persistently growing peaks in electron PSD. While enhancements of ultra-relativistic electrons in other two events still show energy-dependent phenomenon, our results provide the observation evidence that one-step local acceleration process can lead to the enhancement of ∼7 MeV electrons in some events. We suggest that the acceleration process of ultra-relativistic electrons may be subject to the efficiency of local acceleration.

Abstract Image

外辐射带中心超相对论电子的一步式局部加速过程:观测
超相对论(3MeV)电子被认为是地球辐射带中一个新的、独立的群体,因为它们的损耗和加速特征与相对论(∼MeV)电子截然不同。超相对论电子的主要加速机制仍是一个争论不休的话题。一些研究表明,超相对论电子的加速机制与能量有关:局部加速对 ∼3-5 MeV 电子的增强起主导作用,而对于 ∼7 MeV 电子,则是由径向扩散效应主导的两步加速过程。然而,最近的一项研究(https://doi.org/10.1126/sciadv.abc0380)从理论上证明,在等离子体极度耗竭的情况下,局部加速可以直接将电子加速到 7 MeV。在本研究中,我们报告了2017年9月和10月发生的四次超相对论电子增强事件。对相空间密度(PSD)径向剖面和等值线的分析表明,在9月中旬和10月中旬的7 MeV以下电子增强事件中,局域加速起了主导作用,电子PSD持续增长的峰值为其提供了支持。虽然在其他两个事件中超相对论电子的增强仍然表现出能量依赖现象,但我们的结果提供了观测证据,即一步局部加速过程可以导致某些事件中7 MeV∼电子的增强。我们认为超相对论电子的加速过程可能受制于局部加速的效率。
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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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