Radial transport in the outer radiation belt due to global magnetospheric compressions
Radial transport in the outer radiation belt due to global magnetospheric compressions
复制标题
由于全球磁层压缩导致外辐射带的径向传输
DOI：
10.1016/j.jastp.2008.07.018
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
M. Sitnov
中科院分区：
文献类型：
--
作者：
A. Ukhorskiy;M. Sitnov
地球的外辐射带充满了相对论电子，这些电子对不同的地磁活动产生复杂的动态响应。定义带整体状态的一个基本过程是电子穿过其漂移壳层的径向传输。径向传输是由电子漂移运动与电场和磁场的超低频振荡的共振相互作用引起的，并且通常被认为是一个扩散过程。本文的目标是分析内磁层场中典型 ULF 涨落引起的径向输运。为此，在引导中心近似中使用测试粒子方法。我们特别考虑由全球磁层压缩引起的超低频振荡。结果表明，典型的压力变化会引起磁场和感应电场的大规模波动，从而对相对论电子产生重大影响。由于漂移共振附近的电子群与场谱的相邻谐波重叠，电子运动变得随机。结果表明，尽管存在潜在的随机性，但在外辐射带中仍无法完全达到径向扩散极限。这是由于系统尺寸有限，电子运动中的相位相关性没有时间衰减。结果，外带电子的集体运动可能表现出与径向扩散的较大偏差。为了准确描述带中的径向传输，需要解出完整的刘维尔方程。
Earth's outer radiation belt is populated by relativistic electrons that produce a complex dynamical response to varying geomagnetic activity. One fundamental process defining global state of the belt is radial transport of electrons across their drift shells. Radial transport is induced by resonant interaction of electron drift motion with ULF oscillations of electric and magnetic fields and is commonly believed to be a diffusive process. The goal of this paper is the analysis of radial transport due to typical ULF fluctuations in the inner magnetospheric fields. For this purpose a test-particle approach is used in the guiding center approximation. In particular we consider ULF oscillations due to global magnetospheric compressions. It is shown that typical pressure variations induce large-scale fluctuations in magnetic and inductive electric fields that produce a substantial impact on relativistic electrons. Electron motion becomes stochastic due to overlap of electron populations trapped in the vicinities of drift resonances with adjacent harmonics of the field spectrum. It is shown that in spite of the underlying stochasticity the radial diffusion limit is not fully attainable in the outer radiation belt. This is attributed to the fact that phase correlations in electron motion do not have time to decay due to finite size of the system. As a result collective motion of the outer belt electrons can exhibit large deviations from radial diffusion. Solution of the full Liouville's equation is required for accurate description of radial transport in the belt.