Auroral arcs and diffuse auroras are common phenomena at high latitudes, though characteristics of their source plasma and fields have not been well understood. We report the first observation of fields and particles including their pitch‐angle distributions in the source region of auroral arcs and diffuse auroras, using data from the Arase satellite at L  ~ 6.0–6.5. The auroral arcs appeared and expanded both poleward and equatorward at local midnight from ~0308 UT on 11 September 2018 at Nain (magnetic latitude: 66°), Canada, during the expansion phase of a substorm, while diffuse auroras covered the whole sky after 0348 UT. The top part of auroral arcs was characterized by purple/blue emissions. Bidirectional field‐aligned electrons with structured energy‐time spectra were observed in the source region of auroral arcs, while source electrons became isotropic and less structured in the diffuse auroral region afterwards. We suggest that structured bidirectional electrons at energies below a few keV were caused by upward field‐aligned potential differences (upward electric field along geomagnetic field) reaching high altitudes (~30,000 km) above Arase. The bidirectional electrons above a few keV were probably caused by Fermi acceleration associated with the observed field dipolarization. Strong electric‐field fluctuations and earthward Poynting flux were observed at the arc crossing and are probably also caused by the field dipolarization. The ions showed time‐pitch‐angle dispersion caused by mirror reflection. These results indicate a clear contrast between auroral arcs and diffuse auroras in terms of source plasma and fields and generation mechanisms of auroral arcs in the inner magnetosphere.

中文翻译：

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磁层内极光弧和弥散极光源区域的观测观测

在高纬度地区，极光弧和弥散极光是常见现象，尽管其源等离子体和场的特征尚未得到很好的理解。我们使用来自Arase卫星在L处的数据，报告了首次观察到的场和粒子，包括其在极光弧和弥散极光源区域中的俯仰角分布。 〜6.0–6.5。在亚暴的扩张阶段，从2018年9月11日在加拿大Nain（磁纬度：66°）的〜0308 UT在当地午夜，极光弧出现并向北极和赤道方向扩展，而0348年之后弥散的极光覆盖了整个天空UT。极光弧的顶部以紫色/蓝色发射为特征。在极光弧的源区中观察到具有结构化的能量-时间谱的双向场取向电子，而之后在扩散的极光区中，源电子变得各向同性且结构化程度较低。我们认为，能量低于几keV的结构化双向电子是由向上磁场对准的电势差（沿地磁场的向上电场）到达Arase之上的高海拔（约30,000 km）引起的。几个keV以上的双向电子可能是由与观察到的场双极化有关的费米加速度引起的。在电弧交叉处观察到强烈的电场波动和向地球的波因廷通量，这很可能也是由场极化引起的。离子显示出由镜面反射引起的时间间距角分散。这些结果表明，在内部磁层中，在源等离子体和场以及极弧的产生机理方面，极光弧和弥散极光之间存在明显的对比。离子表现出由镜面反射引起的时间间距角分散。这些结果表明，在源磁极和内磁层中极光弧和弥散极光之间，在源等离子体和场以及极光弧的产生机理方面存在明显的对比。离子显示出由镜面反射引起的时间间距角分散。这些结果表明，在源磁极和内磁层中极光弧和弥散极光之间，在源等离子体和场以及极光弧的产生机理方面存在明显的对比。