A multi-scale magnetotail reconnection event at Saturn and associated flows: Cassini/UVIS observations
A multi-scale magnetotail reconnection event at Saturn and associated flows: Cassini/UVIS observations
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DOI：
10.1016/j.icarus.2014.12.016
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发表时间：
2016
期刊：
影响因子：
3.2
通讯作者：
A. Radioti;D. Grodent;X. Jia;J. Gérard;B. Bonfond;W. Pryor;J. Gustin;D. Mitchell;C. Jackman
中科院分区：
文献类型：
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作者：
A. Radioti;D. Grodent;X. Jia;J. Gérard;B. Bonfond;W. Pryor;J. Gustin;D. Mitchell;C. Jackman
我们提出了高分辨率卡西尼/紫外线成像光谱仪（UVIS）观测土星的极光在2013年5月（DOY 140-141）。观测结果表明，在一个扩大的当地时间扇区（02 - 05 LT）的午夜-黎明象限，极光活动增强，其旋转的平均速度为刚性共转的1.45%。这里报告的极光黎明增强，考虑到其观测到的位置和亮度，最有可能是由于热稀薄等离子体携带向内快速移动的通量管返回从尾部重连网站的阳面。这些通量管可以产生强烈的场向电流，导致极光变亮。然而，尾部重联的起源（太阳风或内部驱动）是不确定的。主要基于通量的变化，这并不表明通量关闭，我们认为，最合理的情况是内部驱动的尾部重联封闭的磁力线上运行。观测结果还揭示了增强区域内的多次增强，表明尾部有一条x线，从02 LT延伸到05 LT。局部增强演变成弧形和斑点状的小尺度特征，主要在序列开始时类似于漩涡。这些极光特征可能与等离子体流增强，从重联分叉成多个狭窄的通道，然后蔓延的方位角和径向。我们认为，在土星的尾巴重连接的演变可能被描绘成一个合奏的许多狭窄的电流楔或向内运输开始在重连接区域可以解释由多个本地化的流量爆发事件。涡状结构的形成可能与场向电流有关，在尾部的涡流中形成。另一种不太可能的情况是，小尺度极光结构与涉及小尺度重连的粘性相互作用有关。
We present high-resolution Cassini/UVIS (Ultraviolet Imaging Spectrograph) observations of Saturn’s aurora during May 2013 (DOY 140–141). The observations reveal an enhanced auroral activity in the midnight-dawn quadrant in an extended local time sector (∼02 to 05 LT), which rotates with an average velocity of ∼45% of rigid corotation. The auroral dawn enhancement reported here, given its observed location and brightness, is most probably due to hot tenuous plasma carried inward in fast moving flux tubes returning from a tail reconnection site to the dayside. These flux tubes could generate intense field-aligned currents that would cause aurora to brighten. However, the origin of tail reconnection (solar wind or internally driven) is uncertain. Based mainly on the flux variations, which do not demonstrate flux closure, we suggest that the most plausible scenario is that of internally driven tail reconnection which operates on closed field lines. The observations also reveal multiple intensifications within the enhanced region suggesting an x-line in the tail, which extends from 02 to 05 LT. The localised enhancements evolve in arc and spot-like small scale features, which resemble vortices mainly in the beginning of the sequence. These auroral features could be related to plasma flows enhanced from reconnection which diverge into multiple narrow channels then spread azimuthally and radially. We suggest that the evolution of tail reconnection at Saturn may be pictured by an ensemble of numerous narrow current wedges or that inward transport initiated in the reconnection region could be explained by multiple localised flow burst events. The formation of vortical-like structures could then be related to field-aligned currents, building up in vortical flows in the tail. An alternative, but less plausible, scenario could be that the small scale auroral structures are related to viscous interactions involving small-scale reconnection.