Investigating the source of near‐relativistic and relativistic electrons in Earth's inner radiation belt
Investigating the source of near‐relativistic and relativistic electrons in Earth's inner radiation belt
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研究地球内部辐射带中近相对论和相对论电子的来源
DOI：
10.1002/2016ja023600
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
G. Reeves
中科院分区：
文献类型：
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作者：
D. Turner;T. O'Brien;J. Fennell;S. Claudepierre;J. Blake;A. Jaynes;D. Baker;S. Kanekal;M. Gkioulidou;M. Henderson;G. Reeves
利用 NASA 范艾伦探测器的观测结果，我们研究了低 L 壳层 (SPELLS) 处的粒子突然增强作为内辐射带电子源的作用。 SPELLS 事件的特征是电子强度在 L < 3 的时间内在不到 1 天的时间内增强大约一个数量级或更多。在安静和平均地磁条件下，对于能量范围从 ~50 keV 到 ~1 MeV 的电子，固定第一和第二绝热不变量的相空间密度径向分布在 2 < L < 3 处达到峰值，表明向内缓慢在安静/平均条件下，径向扩散不是内带电子的主要来源。在SPELLS事件期间，电子分布的演变揭示了相空间密度的增强，在槽区域中可以超过3个数量级，并继续进入内辐射带，这证明这些事件是内带电子的重要且潜在的主导来源。 2012 年 9 月至 2016 年 2 月的电子通量表明，SPELLS 频繁发生（200 keV 时约为 2.5 个/月），但随着电子能量≥100 keV 的增加，观察到的事件数量呈指数下降。在 SPELLS 事件之后，由于在几天的时间尺度内缓慢的能量依赖性衰减，槽区域会发生重组，这与由于与等离子层嘶嘶声相互作用而造成的损失一致。综合起来，这些结果表明，内部电子辐射带中的峰值相空间密度分布是由来自较高径向距离的“开/关”地磁活动相关源造成的。
Using observations from NASA's Van Allen Probes, we study the role of sudden particle enhancements at low L shells (SPELLS) as a source of inner radiation belt electrons. SPELLS events are characterized by electron intensity enhancements of approximately an order of magnitude or more in less than 1 day at L < 3. During quiet and average geomagnetic conditions, the phase space density radial distributions for fixed first and second adiabatic invariants are peaked at 2 < L < 3 for electrons ranging in energy from ~50 keV to ~1 MeV, indicating that slow inward radial diffusion is not the dominant source of inner belt electrons under quiet/average conditions. During SPELLS events, the evolution of electron distributions reveals an enhancement of phase space density that can exceed 3 orders of magnitude in the slot region and continues into the inner radiation belt, which is evidence that these events are an important—and potentially dominant—source of inner belt electrons. Electron fluxes from September 2012 through February 2016 reveal that SPELLS occur frequently (~2.5/month at 200 keV), but the number of observed events decreases exponentially with increasing electron energy for ≥100 keV. After SPELLS events, the slot region reforms due to slow energy‐dependent decay over several day time scales, consistent with losses due to interactions with plasmaspheric hiss. Combined, these results indicate that the peaked phase space density distributions in the inner electron radiation belt result from an “on/off,” geomagnetic‐activity‐dependent source from higher radial distances.