Realistic Electron Diffusion Rates and Lifetimes Due to Scattering by Electron Holes
Realistic Electron Diffusion Rates and Lifetimes Due to Scattering by Electron Holes
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DOI：
10.1029/2021ja029380
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发表时间：
2021-08
期刊：
影响因子：
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通讯作者：
Yangyang Shen;I. Vasko;A. Artemyev;D. Malaspina;X. Chu;V. Angelopoulos;Xiao‐jia Zhang
中科院分区：
文献类型：
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作者：
Yangyang Shen;I. Vasko;A. Artemyev;D. Malaspina;X. Chu;V. Angelopoulos;Xiao‐jia Zhang
等离子体片电子沉淀到漫射极光中对于磁层-电离层耦合至关重要。最近的研究表明，电子相空间空穴可以俯仰角散射电子，并可能产生等离子体片电子沉淀。这些研究假设了相同的电子空穴参数来估计电子散射速率（Vasko等人，2018，https：//doi.org/10.1063/1.5039687）。在这项研究中，我们重新评估了这种散射的效率，将来自直接航天器观测的真实电子空穴特性纳入计算电子扩散速率和寿命。在该评估中，最重要的电子空穴特性是它们在速度和空间尺度上的分布以及电场均方根强度（Ew）。利用货车艾伦探针在R_（6 RE）观测到的等离子体注入过程中电子空穴的直接测量，我们发现当Ew≥ 4 mV/m时，电子寿命可以下降到1 h以下，并且在能量低于10 keV时，大多数处于强扩散极限内。在THEMIS航天器在R 12 RE观测到的注入过程中，即使是典型强度（Ew≥ 1 mV/m）的电子空穴也可以在注入和尾部对流后的几十分钟内耗尽低能（<几keV）等离子体片电子。我们的研究结果证实，电子空穴是一个显着的贡献等离子体片电子沉淀在注射过程中。
Plasma sheet electron precipitation into the diffuse aurora is critical for magnetosphere‐ionosphere coupling. Recent studies have shown that electron phase space holes can pitch‐angle scatter electrons and may produce plasma sheet electron precipitation. These studies have assumed identical electron hole parameters to estimate electron scattering rates (Vasko et al., 2018, https://doi.org/10.1063/1.5039687). In this study, we have re‐evaluated the efficiency of this scattering by incorporating realistic electron hole properties from direct spacecraft observations into computing electron diffusion rates and lifetimes. The most important electron hole properties in this evaluation are their distributions in velocity and spatial scale and electric field root‐mean‐square intensity ( Ew ). Using direct measurements of electron holes during a plasma injection event observed by the Van Allen Probe at R∼6RE , we find that when Ew≥ 4 mV/m electron lifetimes can drop below 1 h and are mostly within strong diffusion limits at energies below ∼ 10 keV. During an injection observed by the THEMIS spacecraft at R∼12RE , electron holes with even typical intensities ( Ew≥ 1 mV/m) can deplete low‐energy ( < a few keV) plasma sheet electrons within tens of minutes following injections and convection from the tail. Our results confirm that electron holes are a significant contributor to plasma sheet electron precipitation during injections.