Imajo Shun, Miyoshi Yoshizumi, Kazama Yoichi, Asamura Kazushi, Shinohara Iku, Shiokawa Kazuo, Kasahara Yoshiya, Kasaba Yasumasa, Matsuoka Ayako, Wang Shiang-Yu, Tam Sunny W Y, Chang Tzu-Fang, Wang Bo-Jhou, Angelopoulos Vassilis, Jun Chae-Woo, Shoji Masafumi, Nakamura Satoko, Kitahara Masahiro, Teramoto Mariko, Kurita Satoshi, Hori Tomoaki
Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8601, Japan.
Academia Sinica Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, AS/NTU, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617, Taiwan.
Sci Rep. 2021 Jan 18;11(1):1610. doi: 10.1038/s41598-020-79665-5.
Bright, discrete, thin auroral arcs are a typical form of auroras in nightside polar regions. Their light is produced by magnetospheric electrons, accelerated downward to obtain energies of several kilo electron volts by a quasi-static electric field. These electrons collide with and excite thermosphere atoms to higher energy states at altitude of ~ 100 km; relaxation from these states produces the auroral light. The electric potential accelerating the aurora-producing electrons has been reported to lie immediately above the ionosphere, at a few altitudes of thousand kilometres. However, the highest altitude at which the precipitating electron is accelerated by the parallel potential drop is still unclear. Here, we show that active auroral arcs are powered by electrons accelerated at altitudes reaching greater than 30,000 km. We employ high-angular resolution electron observations achieved by the Arase satellite in the magnetosphere and optical observations of the aurora from a ground-based all-sky imager. Our observations of electron properties and dynamics resemble those of electron potential acceleration reported from low-altitude satellites except that the acceleration region is much higher than previously assumed. This shows that the dominant auroral acceleration region can extend far above a few thousand kilometres, well within the magnetospheric plasma proper, suggesting formation of the acceleration region by some unknown magnetospheric mechanisms.
明亮、离散、纤细的极光弧是夜侧极区极光的典型形态。它们的光是由磁层电子产生的，这些电子在准静态电场作用下向下加速，获得几千电子伏特的能量。这些电子与热层原子碰撞并将其激发到更高的能量状态，在约100千米的高度；从这些状态的弛豫产生极光。据报道，加速产生极光的电子的电势位于电离层正上方，在几千千米的几个高度处。然而，通过平行电势降加速沉淀电子的最高高度仍不清楚。在这里，我们表明活跃的极光弧是由在高于30000千米的高度加速的电子提供能量的。我们利用了Arase卫星在磁层中获得的高角分辨率电子观测数据以及地面全天空成像仪对极光的光学观测数据。我们对电子特性和动力学的观测类似于从低空卫星报道的电子电势加速情况，只是加速区域比之前假设的要高得多。这表明主要的极光加速区域可以延伸到几千千米以上，深入磁层等离子体内部，这表明加速区域是由一些未知的磁层机制形成的。
