The Mysterious Green Streaks Below STEVE
The Mysterious Green Streaks Below STEVE
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史蒂夫脚下神秘的绿色条纹
DOI：
10.1029/2020av000183
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发表时间：
2020
期刊：
影响因子：
8.4
通讯作者：
Wang, Jun
中科院分区：
文献类型：
--
作者：
Semeter, Joshua;Hunnekuhl, Michael;MacDonald, Elizabeth;Hirsch, Michael;Zeller, Neil;Chernenkoff, Alexei;Wang, Jun
强热发射速度增强(STEAT)是离子漂移速度引起的极光下电离层的一种光学现象。在真彩色图像中，STEVE由两个截然不同的部分组成：一个是沿磁东西方向延伸的紫红色或白色弧线，另一个是靠近弧线的绿色发射区，通常被构造成与地磁场对齐的准周期柱状(“尖桩栅栏”)。这项工作使用了公民科学家的高分辨率图像，对绿色发射区域内的精细特征进行了严格的检查。特别令人感兴趣的是，在100至110公里的高度范围内，在野外对准的桩栅栏下形成了狭窄的排放“条纹”。条纹以弯曲的轨迹传播，从极地一侧向史蒂夫方向占主导地位。伸长沿运动方向，暗示着漂移的点状激发源，由于运动模糊和辐射寿命效应的组合，明显的伸长。横截面尺寸为<；1 公里，观察到的事例持续时间为20-30 S。在这些事件中所有史蒂夫绿特征的均匀着色表明了由氧557.7 nm发射线主导的共同光谱。最有可能的来源是由驱动史蒂夫的极端电场诱导的电离层湍流产生的超热电子对环境氧的直接激发。基于热不稳定性和梯度漂移不稳定性的耦合，提出了一些关于与上覆场向结构有因果联系的猜想，类似于从化学释放和电离层加热实验中观察到的动力学。
Strong thermal emission velocity enhancement (STEVE) is an optical phenomenon of the subauroral ionosphere arising from extreme ion drift speeds. STEVE consists of two distinct components in true‐color imagery: a mauve or whitish arc extended in the magnetic east–west direction and a region of green emission adjacent to the arc, often structured into quasiperiodic columns aligned with the geomagnetic field (the “picket fence”). This work employs high‐resolution imagery by citizen scientists in a critical examination of fine‐scale features within the green emission region. Of particular interest are narrow “streaks” of emission forming underneath field‐aligned picket fence elements in the 100‐ to 110‐km altitude range. The streaks propagate in curved trajectories with dominant direction toward STEVE from the poleward side. The elongation is along the direction of motion, suggesting a drifting point‐like excitation source, with the apparent elongation due to a combination of motion blur and radiative lifetime effects. The cross‐sectional dimension is <1 km, and the cases observed have a duration of20–30 s. The uniform coloration of all STEVE green features in these events suggests a common optical spectrum dominated by the oxygen 557.7‐nm emission line. The source is most likely direct excitation of ambient oxygen by superthermal electrons generated by ionospheric turbulence induced by the extreme electric fields driving STEVE. Some conjectures about causal connections with overlying field‐aligned structures are presented, based on coupling of thermal and gradient‐drift instabilities, with analogues to similar dynamics observed from chemical release and ionospheric heating experiments.
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作者：
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