Signature of Saturn's auroral cusp:simultaneous Hubble Space Telescope FUV observations and upstream solar wind monitoring
Signature of Saturn's auroral cusp:simultaneous Hubble Space Telescope FUV observations and upstream solar wind monitoring
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土星极光尖头的特征：同步哈勃太空望远镜FUV观测和上游太阳风监测
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
S. Badman
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作者：
J. Gérard;E. Bunce;D. Grodent;S. Cowley;J. Clarke;S. Badman
[1] Bunce 等人的模型模拟。 (2005a) 表明，土星日侧尖点区域的电子直接沉淀无法产生显着的 FUV 极光。相反，他们提出了一种可能性，即有时在中午附近观察到的 FUV 亮发射与日侧磁层顶发生的重新连接有关，可能是脉冲的，类似于在地球上看到的通量转移事件。当IMF指向北（与土星磁力线反平行）时，低纬度日侧磁层顶的脉冲重联预计将在磁层中产生脉冲双涡流，从而产生以电离层佩德森电流闭合的涡流为中心的双极场对准电流。在南向 IMF 和高纬度波瓣重新连接的情况下，与前一种情况相比，模型预测涡流将向开闭场线边界的极地方向移动，并具有相反的场对准电流。 2004年1月，进行了一次独特的活动，卡西尼-惠更斯号宇宙飞船上的磁场和等离子体仪器测量了原位太阳风和嵌入的行星际磁场，而哈勃太空望远镜同时观测了土星南半球的远紫外极光。在此期间，国际货币基金组织的结构是高度结构化的。卡西尼号的电势是根据低纬度或波瓣重联情况下的太阳风磁场和速度测量来估计的。我们表明，在小压缩期期间，当日面重联电压估计为~30-100 kV时，在主椭圆形的极向或沿主椭圆形发现了强电子降水的日面FUV特征。总的来说，我们发现 Bunce 等人的概念模型。 (2005a) 提供了对北向 IMF 情况下的 UV 亮度和功率的良好估计，但在某种程度上低估了南向 IMF 情况下的功率，除非旋涡流的速度大于其在标称模型中的值。
[1] Model simulations by Bunce et al. (2005a) have shown that direct precipitation of electrons in Saturn's dayside cusp regions is not capable of producing significant FUV aurora. Instead, they suggested the possibility that the FUV bright emissions sometimes observed near noon are associated with reconnection occurring at the dayside magnetopause, possibly pulsed, analogous to flux transfer events seen at the Earth. Pulsed reconnection at the low-latitude dayside magnetopause when the IMF is directed northward (antiparallel to Saturn's magnetic field lines) is expected to give rise to pulsed twin-vortical flows in the magnetosphere and hence to bipolar field-aligned currents centered in the vortical flows closing in ionospheric Pedersen current. In the case of southward IMF and high-latitude lobe reconnection the model predicts that the vortical flows are displaced poleward of the open-closed field line boundary with reversed field-aligned currents compared with the former case. During January 2004, a unique campaign took place during which magnetic field and plasma instruments on board the Cassini-Huygens spacecraft measured the in situ solar wind and embedded interplanetary magnetic field while the Hubble Space Telescope simultaneously observed the far ultraviolet aurora in Saturn's southern hemisphere. The IMF was highly structured during this interval. The electric potential at Cassini is estimated from solar wind magnetic field and velocity measurements for the case of low-latitude or lobe reconnection. We show that a dayside FUV signature of intense electron precipitation is found poleward of or along the main oval during a period of minor compression period when the dayside reconnection voltage is estimated to be ∼30–100 kV. Overall, we find that the conceptual model of Bunce et al. (2005a) provides a good estimate of the UV brightness and power for the case of northward IMF but somewhat underestimates the power for the southward IMF case, except if the speed of the vortical flow is larger than its value in the nominal model.