Simultaneous conjugate observations of small‐scale structures in Saturn's dayside ultraviolet auroras: Implications for physical origins
Simultaneous conjugate observations of small‐scale structures in Saturn's dayside ultraviolet auroras: Implications for physical origins
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土星日侧紫外线极光小尺度结构的同时共轭观测：对物理起源的影响
DOI：
10.1002/jgra.50270
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
T. Yeoman
中科院分区：
文献类型：
--
作者：
C. Meredith;S. Cowley;K. C. Hansen;Jonathan D. Nichols;T. Yeoman
利用哈勃太空望远镜在接近土星春分的32次观测中获得的图像，研究了土星日侧紫外线极光的小尺度特征，当时同时观测到南北发射，从而研究了它们的半球间共轭。在大约70%的观测中，在黎明至正午区域观测到向东传播的斑块，当它们出现时，几乎总是在北方和南方观测到。然而，斑块通常不是紧密共轭的，但在当地时间通常会发生~ 0.5-1 h的位移，其中一个半球的最大值在另一个半球的最小值附近。平均角速度约为刚性自转的80%，比外磁层报道的等离子体角速度要大，因为外磁层的辐射可能与等离子体角速度共轭。我们认为这些斑块与向东传播的ULF波的场向电流有关，特别是具有典型方位角波数m≈20和等离子体静止框架周期~80分钟的二次谐波alfv<s:1>谐振，可能是由热磁层水离子的漂移-弹跳共振驱动的。在约40%的观测中也观察到持续时间约10-30分钟的短暂黄昏扇区排放，并发现这是严格的非共轭现象，北半球或南半球的增强并不伴随着另一个半球的增强。我们提出了与开放通量管的关联，并讨论了一种情况，即半球对称性通过行星际磁场Y分量在新打开的通量管上被打破，似乎与南北非共轭事件一致，优先发生在中午后，时间尺度为几十分钟，尽管与Y分量的预期关系仍有待建立。
Small‐scale features in Saturn's dayside UV auroras are examined using images obtained on 32 Hubble Space Telescope visits close to Saturn equinox when both northern and southern emissions were simultaneously observed, allowing their interhemispheric conjugacy to be investigated. Eastward‐propagating patches in the dawn‐to‐noon sector were observed on ~70% of visits, which when present were nearly always observed both north and south. The patches were generally not closely conjugate, however, but typically displaced in local time by ~0.5–1 h, with maxima in one hemisphere falling near minima in the other. Averaged angular velocities were ~80% of rigid corotation, larger than plasma angular velocities reported in the outer magnetosphere to which the emissions are likely conjugate. We suggest the patches are associated with field‐aligned currents of eastward‐propagating ULF waves, specifically second harmonic Alfvén resonances with typical azimuthal wave numbers m ≈ 20 and plasma rest frame periods ~80 min, plausibly driven by drift‐bounce resonance with hot magnetospheric water ions. Transient dusk sector emissions of ~10–30 min duration were also observed on ~40% of visits, and found to be strictly nonconjugate, with enhancements in one hemisphere, north or south, being unaccompanied by enhancements in the other. We suggest an association with open flux tubes, and discuss one scenario where hemispheric symmetry is broken on newly opened flux tubes via the interplanetary magnetic field Y component, plausibly consistent with nonconjugate events north and south, preferential postnoon occurrence, and time scales of a few tens of minutes, though the expected relationship with the Y component remains to be established.
DOI：
10.1029/2008ja013257
发表时间：
2008-09
期刊：
Scopus
影响因子：
--
作者：
E. Bunce;C. Arridge;J. Clarke;A. Coates;S. Cowley;M. Dougherty;Jean-Claude Gérard;D. Grodent;K. Hansen;J. Nichols;D. Southwood;D. Southwood;D. Talboys
通讯作者：
E. Bunce;C. Arridge;J. Clarke;A. Coates;S. Cowley;M. Dougherty;Jean-Claude Gérard;D. Grodent;K. Hansen;J. Nichols;D. Southwood;D. Southwood;D. Talboys
土星白天磁层的磁场结构及其到电离层的映射：环流模型的结果
DOI：
10.1029/2007ja012538
发表时间：
2008
期刊：
Space Physics
影响因子：
--
作者：
Bunce E
通讯作者：
Bunce E
影响因子：
5.2
作者：
Burton M
通讯作者：
Burton M