Pulsating aurora from electron scattering by chorus waves
Pulsating aurora from electron scattering by chorus waves
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DOI：
10.1038/nature25505
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发表时间：
2018-02-15
期刊：
影响因子：
64.8
通讯作者：
Shinohara, I.
中科院分区：
文献类型：
--
作者：
Kasahara, S.;Miyoshi, Y.;Shinohara, I.
极光亚暴是夜间高层大气中发生的动态现象，是由磁层的全球重新配置引起的，磁层释放了储存的太阳风能(1,2)。这些风暴的特点是从黄昏到午夜极光变亮，随后是明显的极光弧剧烈运动并突然破裂，随后在黎明时出现弥散的脉动极光斑(1,3)。脉动极光是准周期性的闪烁光斑，直径数十至数百公里，出现在两个半球高纬度地区约100公里的高度，并且多个光斑经常覆盖整个天空。这种极光脉动的周期为几秒到几十秒，是由来自磁层的高能电子（几千电子伏特）间歇性沉淀而产生的，并与高层大气的原子和分子碰撞(4-7)。造成这种降水的一个可能原因是磁层电子与称为哨声模式合唱波的电磁波之间的相互作用(8-11)。然而，迄今为止尚未获得这种相互作用的直接观察证据(12)。在这里，我们报告高能电子被合唱波散射，导致其沉淀。我们于 2017 年 3 月使用配备高角分辨率电子传感器和电磁场仪器的磁层航天器进行了观测。测量到的(13,14)准周期沉淀电子通量足以产生脉动极光，地面极光成像仪确实同时观测到了脉动极光。
Auroral substorms, dynamic phenomena that occur in the upper atmosphere at night, are caused by global reconfiguration of the magnetosphere, which releases stored solar wind energy(1,2). These storms are characterized by auroral brightening from dusk to midnight, followed by violent motions of distinct auroral arcs that suddenly break up, and the subsequent emergence of diffuse, pulsating auroral patches at dawn(1,3). Pulsating aurorae, which are quasiperiodic, blinking patches of light tens to hundreds of kilometres across, appear at altitudes of about 100 kilometres in the high-latitude regions of both hemispheres, and multiple patches often cover the entire sky. This auroral pulsation, with periods of several to tens of seconds, is generated by the intermittent precipitation of energetic electrons (several to tens of kiloelectronvolts) arriving from the magnetosphere and colliding with the atoms and molecules of the upper atmosphere(4-7). A possible cause of this precipitation is the interaction between magnetospheric electrons and electromagnetic waves called whistler-mode chorus waves(8-11). However, no direct observational evidence of this interaction has been obtained so far(12). Here we report that energetic electrons are scattered by chorus waves, resulting in their precipitation. Our observations were made in March 2017 with a magnetospheric spacecraft equipped with a high-angular-resolution electron sensor and electromagnetic field instruments. The measured(13,14) quasiperiodic precipitating electron flux was sufficiently intense to generate a pulsating aurora, which was indeed simultaneously observed by a ground auroral imager.