Case studies of the impact of high-speed solar wind streams on the electron radiation belt at geosynchronous orbit: Flux, magnetic field, and phase space density
Case studies of the impact of high-speed solar wind streams on the electron radiation belt at geosynchronous orbit: Flux, magnetic field, and phase space density
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高速太阳风流对地球同步轨道电子辐射带影响的案例研究：通量、磁场和相空间密度
DOI：
10.1002/2013ja018923
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
Hartley D
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作者：
Hartley D
对电子辐射带丢失的调查揭示了许多丢失过程的重要性，但仍然缺乏关于这些过程在事件之间如何增强和减弱的定量细节。这项研究的首要目标是解决电子辐射带脱落的问题。这是通过利用 GOES-13 在地球静止轨道上进行的现场观测（俯仰角分辨电子数据和磁场测量）来检查三个高速流驱动风暴期间的外电子辐射带来实现的。计算作为三个绝热不变量函数的相空间密度 (PSD) 有助于分析和解释。我们的结果证实了向外绝热传输作为导致地球同步轨道电子丢失的机制的重要性；然而，对俯仰角分布的研究表明，在这些高速太阳风流（HSS）驱动的风暴期间也可能发生其他损失机制。研究的两个事件在其俯仰角分布中表现出相似的进化结构：（i）在退出之前立即出现高度峰值分布（ii）峰值和各向同性之间的急剧过渡以及随后的蝴蝶分布，以及（iii）之后不久（黄昏）在最小通量时的各向同性分布。我们还通过将 T96 模型磁场与 GOES-13 测量的磁场进行比较来解决解释 PSD 计算的困难。我们的研究结果旨在作为量化 HSS 到达后辐射带中发生的事件时间线的第一步，特别是考虑到当前太阳周期衰退阶段 HSS 发生的增加预计会增加。
Investigation of electron radiation belt dropouts has revealed the importance of a number of loss processes, yet there remains a lack of quantitative detail as to how these processes wax and wane between events. The overarching aim of this study is to address the issue of electron radiation belt dropouts. This is achieved using in situ observations at geostationary orbit from GOES‐13 (pitch angle‐resolved electron data and magnetic field measurements) to examine the outer electron radiation belt during three high‐speed stream‐driven storms. Analysis and interpretation are aided by calculation of the phase space density (PSD) as a function of the three adiabatic invariants. Our results confirm the importance of outward adiabatic transport as a mechanism for causing electron dropouts at geosynchronous orbit; however, study of the pitch angle distributions indicates that other loss mechanisms are also likely to be occurring during these high‐speed solar wind stream (HSS)‐driven storms. Two of the studied events exhibit similar evolutionary structure in their pitch angle distributions: (i) highly peaked distributions immediately prior to the dropout (ii) sharp transitions between peaked and isotropic and then subsequent butterfly distributions, and (iii) isotropic distributions at minimum flux shortly afterwards (dusk). We also address the difficulty in interpreting PSD calculations by comparing the T96 model magnetic field with that measured by GOES‐13. Our results are intended as a first step in quantifying the timeline of events that occur in the radiation belts following the arrival of a HSS—particularly timely given the increase in HSS occurrence expected in the declining phase of the current solar cycle.