Fine Scale Dynamics of Fragmented Aurora-Like Emission
Fine Scale Dynamics of Fragmented Aurora-Like Emission
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DOI：
10.5194/angeo-2020-95
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发表时间：
2021-01
影响因子：
1.9
通讯作者：
D. Whiter;H. Dahlgren;B. Lanchester;J. Dreyer;N. Partamies;N. Ivchenko;Marco Z. Di Fraia;Rosie Oliver;Amanda Serpell-Stevens;Tiffany Shaw-Diaz;Thomas Braunersreuther
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作者：
D. Whiter;H. Dahlgren;B. Lanchester;J. Dreyer;N. Partamies;N. Ivchenko;Marco Z. Di Fraia;Rosie Oliver;Amanda Serpell-Stevens;Tiffany Shaw-Diaz;Thomas Braunersreuther
抽象的。碎片状极光发射（Fragmented Aurora-like Emissions，FAE）是一种小型（几公里）的光学结构，在斯瓦尔巴特群岛高纬度地区（磁纬75.3 ° N）靠近极光的极向边界处被观测到。FAE仅在某些发射中可见，并且它们的形状没有磁场对齐分量，这表明它们不是由高能粒子沉淀引起的，因此不是正常意义上的极光。FAE有时会形成平行于极光弧的波浪状结构，每个FAE之间有规则的间距。它们以恒定的速度漂移，并表现出比包络结构更快的速度移动的内部动态。FAE的形成机制目前尚不清楚。我们提出了一个分析的高分辨率光学观测的FAE在两个独立的事件。基于它们的外观和动力学，我们假设FAE是在较低的E-区域电离层中的色散波的签名，与增强的电子和离子温度的非相干散射雷达检测到的协同定位。它们的漂移速度（群速度）为580-700 m s-1，它们的内部动力学速度（相速度）为2200-2500 m s-1，两者都是假设高度为100 km。在不同的极光条件下观察到的两个事件的速度是相似的。我们考虑了两种可能产生FAE的波，静电离子回旋波和Farley-Buneman波，并发现在一定的假设下，观测结果与任何一种波都是一致的。在EIC波的情况下，FAE必须位于大约140公里以上的高度，我们测量的速度相应地缩放。在Farley-Buneman波的情况下，需要大约365 mV m−1的非常强的电场来产生FAE的观测速度;这样强的电场可能是FAE发生的必要条件。
Abstract. Fragmented Aurora-like Emissions (FAEs) are small (few km) optical structures which have been observed close to the poleward boundary of the aurora from the high-latitude location of Svalbard (magnetic latitude 75.3 ° N). The FAEs are only visible in certain emissions and their shape has no magnetic-field aligned component, suggesting that they are not caused by energetic particle precipitation and are therefore not aurora in the normal sense of the word. The FAEs sometimes form wave-like structures parallel to an auroral arc, with regular spacing between each FAE. They drift at a constant speed and exhibit internal dynamics moving at a faster speed than the envelope structure. The formation mechanism of FAEs is currently unknown. We present an analysis of high-resolution optical observations of FAEs made during two separate events. Based on their appearance and dynamics we make the assumption that the FAEs are a signature of a dispersive wave in the lower E-region ionosphere, co-located with enhanced electron and ion temperatures detected by incoherent scatter radar. Their drift speed (group speed) is found to be 580–700 m s−1 and the speed of their internal dynamics (phase speed) is found to be 2200–2500 m s−1, both for an assumed altitude of 100 km. The speeds are similar for both events which are observed during different auroral conditions. We consider two possible waves which could produce the FAEs, electrostatic ion cyclotron waves and Farley-Buneman waves, and find that the observations could be consistent with either wave under certain assumptions. In the case of EIC waves the FAEs must be located at an altitude above about 140 km, and our measured speeds scaled accordingly. In the case of Farley-Buneman waves a very strong electric field of about 365 mV m−1 is required to produce the observed speeds of the FAEs; such a strong electric field may be a requirement for FAEs to occur.