Characteristics of Electron Precipitation During 40 Energetic Electron Injections Inferred via Subionospheric VLF Signal Propagation
Characteristics of Electron Precipitation During 40 Energetic Electron Injections Inferred via Subionospheric VLF Signal Propagation
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通过亚电离层 VLF 信号传播推断 40 次高能电子注入过程中的电子沉淀特征
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发表时间：
2020
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通讯作者：
G. Reeves
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作者：
R. Ghaffari;C. Cully;D. Turner;G. Reeves
高能电子注入事件通过可能的共振波粒相互作用与高能电子沉淀（EEP）相关。先前的研究证实了注入驱动降水对从遥远的人工发射机发射的亚电离层 VLF（甚低频）信号观测到的幅度/相位的影响。目前，注入事件期间的降水特征和通量存在很大的不确定性。在这项工作中，我们研究了范艾伦探测器粒子数据选择的 40 个注入事件，以研究粒子注入事件期间加拿大各地地面接收器的 VLF 信号幅度和相位的变化。我们对 EEP 通量的电离层效应进行建模，以找出其对 VLF 传播的影响并描述注入事件的特征。通常，我们发现史密斯堡（加拿大，L = 8）接收到的从美国缅因州的美国海军通信发射机 NAA 发送的 VLF 信号有约 40° 的明显相位超前。与北美其他 VLF 发射机-接收机路径相比，我们得出结论，只有在 L > 7 的足够大范围（≫200 km）的路径上才能看到影响。对 VLF 相位变化建模表明，在大多数事件 (>90%) 中，从范艾伦探测器的粒子通量测量推断出的强散射极限小于 10%，才能获得观测到的 VLF 相位特征。对于从捕获粒子能谱中提取的高于约 40 keV 的电子，高能粒子注入期间的中值沉淀通量小于 4 × 106 el/cm2 s sr（< 强散射率的 10%）。这意味着强散射对于这 40 个选定的高能电子注入事件来说并不典型。
Energetic electron injection events are associated with energetic electron precipitation (EEP) through possible resonant wave‐particle interactions. Previous studies confirm the impacts of injection‐driven precipitation on observed amplitude/phase of subionospheric VLF (very low frequency) signals transmitted from distant artificial transmitters. Currently, there are substantial uncertainties on precipitation characteristics and flux during injection events. In this work we study 40 injection events selected by Van Allen Probes particle data to investigate the changes in amplitude and phase of VLF signals at ground receivers across Canada during particle injection events. We model the ionospheric effect of the EEP flux to find its impact on VLF propagation and characterize the injection events. Typically, we find a clear phase advance of ~40° in the received VLF signal at Fort Smith (Canada, L = 8) transmitted from U.S. Navy communication transmitter NAA at Maine (USA). Comparing to other VLF transmitter‐receiver paths in North America leads us to conclude that effects are only seen on paths with adequately large range ≫200 km) through L > 7. Modeling the VLF phase change indicates that in the majority of events (>90%), less than 10% of the strong scattering limit inferred from particle flux measurements at the Van Allen Probes is required to obtain the observed VLF phase signature. The median precipitating flux during energetic particle injections is less than 4 × 106 el/cm2 s sr (<10% of the strong scattering rate) for electrons above ~40 keV extracted from trapped particles energy spectrum. This implies that strong scattering is not typical for these 40 selected energetic electron injection events.