Characteristics of Jovian morning bright FUV aurora from hubble space telescope/space telescope imaging spectrograph imaging and spectral observations
Characteristics of Jovian morning bright FUV aurora from hubble space telescope/space telescope imaging spectrograph imaging and spectral observations
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哈勃太空望远镜/太空望远镜成像摄谱仪成像和光谱观测的木星早晨明亮FUV极光特征
DOI：
10.1029/2006ja011730
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
J. Clarke
中科院分区：
文献类型：
--
作者：
J. Gustin;J. Gérard;D. Grodent;S. Cowley;G. Gladstone;J. Clarke
[1]1999年9月21日，用空间望远镜成像光谱仪在成像和光谱模式下观测到了一个异常明亮（峰值为1.8兆赫兹）的木星极光晨弧。HST轨道的图像被用来描述亮弧的位置的变化，而时间标记的光谱被检查，以获得沉淀极光电子的属性，如它们的平均能量和在大气层顶部的电子流密度。HST轨道的第一张和最后一张图像相隔37分钟，显示明亮的早晨发射位于参考椭圆上，“领先”边缘固定在λIII轨道上（即，与行星一起旋转），以及延伸到夜面的“后缘”。极光弧分为两个分支，这在之前的一些分析中也观察到了。在λIII <$184 °处还观察到一个孤立的亮点。它的亮度达到500 kR，并且与木星近似共转。从光谱观测中提取了STIS孔径捕获的极光晨弧的四个区域。四个相关的低分辨率光谱（4.8A）显示出非常不同的特性。特别是，两个光谱揭示了异常高的色比（18.5和45.5），相应的平均电子能量分别为1.280和1.460千电子伏。与其中三个光谱相关的电流密度在0.09-0.2 μA m−2之间，与先前的估计一致，而第四个光谱的特征是平均电流密度为0.54 μA m−2，超出了先前对木星主椭圆的G140 L光谱的研究中获得的0.04-0.4 μA m−2范围。假设主要的椭圆形极光是由场向电场引起的，能量通量和来自光谱的电流密度之间的关系已被比较到骑士的场向电流理论。由于非常高的加速潜力来自两个提取的光谱，骑士理论的相对论处理被使用。假设电子温度Te = 2.5 keV，可以看出，对应于较早当地时间（较高λIII时间）的两个区域显示出的电子源密度低于旅行者号飞越期间在赤道平面上观察到的值。另一方面，赤道地区（最低纬度）的电子源密度在正常值的上限范围内。时间标签谱分析表明，能流和色比的变化是大的，但连续的，一般是协变的。
[1] Observation of an exceptionally bright (peaking at ∼1.8 MR) Jovian auroral morning arc was obtained with the Space Telescope Imaging Spectrograph (STIS) on 21 September 1999, both in the imaging and spectral modes. The images of the HST orbit are used to describe the variation of the position of the bright arc, while the time-tagged spectra are examined to derive the properties of the precipitating auroral electrons, such as their mean energy and the electron current density at the top of the atmosphere. The first and the last images of the HST orbit, separated by 37 min, show that the bright morning emission is situated on the reference oval, with a “leading” edge fixed in λIII longitudes (i.e., rotating with the planet), and a “trailing” edge that extends into the nightside. The auroral arc is divided in two branches, as was also observed in some previous analyses. An isolated bright spot is also observed at λIII ∼184°. Its brightness reaches 500 kR and it also approximately corotates with Jupiter. Four regions of the auroral morning arc captured by the STIS aperture were extracted from the spectral observation. The four associated low-resolution spectra (∼4.8 A) show very different characteristics. In particular, two spectra reveal unusually high color ratios (18.5 and 45.5), with corresponding mean electron energies of ∼280 and ∼460 keV, respectively. The current densities associated with three of the spectra lie in the range 0.09–0.2 μA m−2, consistent with previous estimates, while the fourth spectrum is characterized by a mean current density of 0.54 μA m−2, outside the range ∼0.04–0.4 μA m−2 obtained in a previous study of G140L spectra of the Jovian main oval. Assuming that main oval aurorae are caused by field-aligned electric fields, the relationship between the energy flux and the current density derived from the spectra has been compared to the Knight's theory of field-aligned currents. Because of the very high acceleration potential derived from two of the extracted spectra, a relativistic treatment of the Knight theory was used. Assuming an electron temperature Te = 2.5 keV, it is seen that the two regions corresponding to earlier local times (higher λIII longitudes) reveal an electron source density lower than the values observed in the equatorial plane during the Voyager flybys. On the other hand, the equatorward region (lowest latitude) exhibits an electron source density in the upper range of usual values. Analysis of time-tag spectra reveals that the variations of the energy flux and the color ratios are large but continuous and generally covary.