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.

中文翻译：

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极光碎片状发射的精细尺度动力学

摘要。碎片状的极光发射（FAE）是小的（几公里）光学结构，从斯瓦尔巴特群岛的高纬度位置（磁纬度75.3°N）观察到接近极光的极向边界。FAE仅在某些发射中可见，并且它们的形状没有磁场对准的分量，这表明它们不是由高能粒子沉淀引起的，因此在正常意义上不是极光。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，并展现出比包络结构更快的内部动力学。FAE的形成机制目前尚不清楚。

我们提出了在两个独立事件中对FAE进行的高分辨率光学观测的分析。根据它们的外观和动力学，我们假设FAE是低E区电离层中色散波的标志，与非相干散射雷达检测到的增强的电子和离子温度共处一地。发现它们的漂移速度（群速度）为580-700 m s ^-1，发现其内部动力学的速度（相速度）为2200-2500 m s ^-1，两者均假定为100 km。在不同的极光条件下观察到的两个事件的速度相似。我们考虑了可能产生FAE的两种可能的波：静电离子回旋波和Farley-Buneman波，并发现在某些假设下，观测值可能与任一波都一致。对于EIC波，FAE必须位于约140 km以上的高度，并且我们测得的速度会相应地缩放。对于Farley-Buneman波，需要大约365 mV m ^-1的非常强的电场才能产生FAE的观测速度；这样的强电场可能是发生FAE的必要条件。