Arase Observation of the Source Region of Auroral Arcs and Diffuse Auroras in the Inner Magnetosphere
Arase Observation of the Source Region of Auroral Arcs and Diffuse Auroras in the Inner Magnetosphere
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DOI：
10.1029/2019ja027310
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发表时间：
2020-08
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通讯作者：
K. Shiokawa;M. Nosé;S. Imajo;Y.‐M. Tanaka;Y. Miyoshi;K. Hosokawa;M. Connors;M. Engebretson;Y. Kazama;S. Wang;S. Tam;T. Chang;Bo‐Jhou Wang;K. Asamura;S. Kasahara;S. Yokota;T. Hori;K. Keika;Y. Kasaba;M. Shoji;Y. Kasahara;A. Matsuoka;I. Shinohara
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作者：
K. Shiokawa;M. Nosé;S. Imajo;Y.‐M. Tanaka;Y. Miyoshi;K. Hosokawa;M. Connors;M. Engebretson;Y. Kazama;S. Wang;S. Tam;T. Chang;Bo‐Jhou Wang;K. Asamura;S. Kasahara;S. Yokota;T. Hori;K. Keika;Y. Kasaba;M. Shoji;Y. Kasahara;A. Matsuoka;I. Shinohara
极光弧和漫射极光是高纬度地区常见的现象，尽管它们的源等离子体和场的特征还没有被很好地理解。本文报道了利用Arase卫星在L ~ 6.0 ~ 6.5波段的数据，首次观测到极光弧和弥散极光源区的场和粒子，包括它们的俯角分布。从2018年9月11日0308 UT开始，在加拿大Nain（地磁纬度：66°）的当地午夜，在亚暴的扩展阶段，极光弧出现并向极地和赤道方向扩展，而在0348 UT之后，弥漫性极光覆盖了整个天空。极光弧的顶部以紫色/蓝色辐射为特征。在极光弧源区观测到具有结构能谱的双向场向电子，而在扩散极光区观测到的源电子则变得各向同性，结构更少。我们认为，能量低于几keV的结构化双向电子是由到达Arase上空高海拔（~30,000 km）的向上场排列的电位差（沿地磁场向上的电场）引起的。几个keV以上的双向电子可能是由观测到的场双极化相关的费米加速度引起的。在电弧交叉处观察到强电场波动和向地的坡印亭通量，这也可能是由场的双极化引起的。离子表现出由镜面反射引起的时间-节-角色散。这些结果表明，极光弧与漫射极光在源等离子体和场以及内磁层极光弧的产生机制方面存在明显的差异。
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.