Nel A E, Kosch M J, Whiter D, Gustavsson B, Aslaksen T
Centre for Space Research, North-West University, Potchefstroom, 2520, South Africa.
The South African National Space Agency, Hermanus, 7200, South Africa.
Sci Rep. 2021 Jan 19;11(1):1829. doi: 10.1038/s41598-021-81363-9.
Black auroras are small-scale features embedded in the diffuse background aurora, typically occurring post-substorm after magnetic midnight and with an eastward drift imposed. Black auroras show a significant reduction in optical brightness compared to the surrounding diffuse aurora, and can appear as slow-moving arcs or rapidly-moving patches and arc segments. We report, for the first time, an even more elusive small-scale optical structure that has always been observed occurring paired with [Formula: see text] 10% of black aurora patches. A patch or arc segment of enhanced luminosity, distinctly brighter than the diffuse background, which we name the anti-black aurora, may appear adjacent to the black aurora. The anti-black aurora is of similar shape and size, and always moves in parallel to the drifting black aurora, although it may suddenly switch sides for no apparent reason. The paired phenomenon always drifts with the same average speed in an easterly direction. From the first dual-wavelength (427.8 nm and 844.6 nm) optical observations of the phenomenon recorded on 12 March 2016 outside Tromsø Norway, we show that the anti-black and black auroras have a higher and lower mean energy, respectively, of the precipitating electrons compared to the diffuse background.
黑色极光属于嵌入弥散背景极光中的小尺度特征，通常在磁子夜过后的亚暴期间出现，并伴有向东的漂移。与周围的弥散极光相比，黑色极光的光学亮度显著降低，可呈现为缓慢移动的弧形或快速移动的斑块及弧形片段。我们首次报告了一种更为难以捉摸的小尺度光学结构，该结构总是在约10%的黑色极光斑块附近被观测到。一个亮度增强的斑块或弧形片段，明显比弥散背景更亮，我们将其命名为反黑色极光，它可能出现在黑色极光附近。反黑色极光具有相似的形状和大小，并且总是与漂移的黑色极光平行移动，尽管它可能会毫无明显原因地突然改变位置。这种成对现象总是以相同的平均速度向东漂移。通过2016年3月12日在挪威特罗姆瑟郊外记录的该现象的首次双波长（427.8纳米和844.6纳米）光学观测，我们发现与弥散背景相比，反黑色极光和黑色极光的沉降电子平均能量分别更高和更低。
