The present study examines the low-energy ion flux variations observed by the Arase satellite in the inner magnetosphere. From the magnetic field and ion flux data obtained by the fluxgate magnetometer and the low-energy particle experiments–ion mass analyzer onboard Arase, we find 55 events of the low-energy O⁺ flux enhancement accompanied with magnetic field dipolarization in the periods of April 1–October 31, 2017 and July 1, 2018–January 31, 2019. The low-energy O⁺ flux enhancements (a) start a few minutes after the dipolarization onset, (b) have energy-dispersed signatures with decreasing energy from a few keV down to ∼10 eV, (c) are observed in both storm and non-storm periods, (d) have a field-aligned distribution (α ∼ 0° in the southern hemisphere and α ∼ 180° in the northern hemisphere), (e) are accompanied by the low-energy H⁺ flux enhancements that have lower energies than O⁺ by a factor of 3–10, and (f) increase the O⁺ density and the O⁺/H⁺ density ratio by ∼10 times and 4–5 times, respectively. We perform a numerical simulation to trace ion trajectories forward in time from the Arase positions. It is revealed that both H⁺ and O⁺ ions drift eastward and reach the dawn-to-morning sector without being lost in the ionosphere, if the pitch angle scattering effect is considered near the equatorial plane. This result suggests that these low-energy field-aligned ions can contribute to formation of the warm plasma cloak.

中文翻译：

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Arase 观测到的内磁层中场对齐低能 O+ 通量增强

本研究检查了 Arase 卫星在内部磁层中观测到的低能离子通量变化。从磁通门磁力计和Arase低能粒子实验-离子质量分析仪获得的磁场和离子通量数据，我们发现4月期间伴随着磁场偶极的低能O ⁺通量增强的55个事件1，2017年10月31日和2018年7月1日- 2019年一月31日，低能Ø ⁺通量增强（一）开始几分钟偶极发病后，（b）有从减少能量分散能量的签名低至 10 eV 的几个 keV，（c）在风暴和非风暴时期都观察到，（d）具有场对齐分布（α ∼ 0° 在南半球，α  ∼ 180° 在北半球），(e) 伴随着能量比 O ⁺低3-10 倍的低能 H ⁺通量增强，和 (f ) 将 O ⁺密度和 O ⁺ /H ⁺密度比分别增加约 10 倍和 4-5 倍。我们执行数值模拟以从 Arase 位置及时追踪离子轨迹。结果表明，H ⁺和 O ⁺如果在赤道平面附近考虑俯仰角散射效应，则离子向东漂移并到达黎明至早晨的扇区而不会在电离层中丢失。这一结果表明，这些低能场排列的离子有助于形成温暖的等离子体斗篷。