The magnetic local time distribution of energetic electrons in the radiation belt region
The magnetic local time distribution of energetic electrons in the radiation belt region
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DOI：
10.1002/2017ja024084
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发表时间：
2017-08
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影响因子：
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通讯作者：
H. Allison;R. Horne;S. Glauert;G. Zanna
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文献类型：
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作者：
H. Allison;R. Horne;S. Glauert;G. Zanna
利用美国国家海洋和大气管理局极地业务环境卫星14年的电子通量数据，对电子种群在一系列活动水平上的磁地方时（MLT）分布进行了统计研究，这些活动水平由AE、AE*、Kp、太阳风速度（Vsw）和VswBz定义。考虑了三种电子能量（bbb30, >00, bbb300 keV）。在bbb30和>00 keV的电子中观测到大于数量级的黎明-黄昏通量不对称。对于bbb300 keV的电子，黎明-黄昏不对称主要是由于平均黄昏通量随着活动的增加而减少，超过L* ~ 4.5。对于bbb30kev的粒子群，亚暴注入增强了黎明侧的通量，但由于电子可能在开放的漂移路径上并丢失到磁层顶，因此可能无法到达黄昏侧。>300 keV居群的不对称性是由磁层顶遮蔽和>300 keV大电场电子注入共同作用的结果。我们建议三维辐射带模型可以在低活跃期L* ~ 6处将最小能量边界（Emin）设置为30 keV或更高。然而，对于更温和的条件，Emin应大于100 keV，对于非常极端的活动，Emin应大于300 keV。我们的观测表明，由于卫星的MLT，在活动期间，原位电子通量读数可能会发生一定程度的变化，并强调了4 - D辐射带模型对充分理解辐射带过程的重要性。
Using 14 years of electron flux data from the National Oceanic and Atmospheric Administration Polar Operational Environmental Satellites, a statistical study of the magnetic local time (MLT) distribution of the electron population is performed across a range of activity levels, defined by AE, AE*, Kp, solar wind velocity (Vsw), and VswBz. Three electron energies (>30, >100, and >300 keV) are considered. Dawn‐dusk flux asymmetries larger than order of magnitude were observed for >30 and >100 keV electrons. For >300 keV electrons, dawn‐dusk asymmetries were primarily due to a decrease in the average duskside flux beyond L* ∼ 4.5 that arose with increasing activity. For the >30 keV population, substorm injections enhance the dawnside flux, which may not reach the duskside as the electrons can be on open drift paths and lost to the magnetopause. The asymmetries in the >300 keV population are attributed to the combination of magnetopause shadowing and >300 keV electron injections by large electric fields. We suggest that 3‐D radiation belt models could set the minimum energy boundary (Emin) to 30 keV or above at L* ∼ 6 during periods of low activity. However, for more moderate conditions, Emin should be larger than 100 keV and, for very extreme activities, ∼300 keV. Our observations show the extent that in situ electron flux readings may vary during active periods due to the MLT of the satellite and highlight the importance of 4‐D radiation belt models to fully understand radiation belt processes.