Auroral electron precipitation and flux tube erosion in Titan’s upper atmosphere
Auroral electron precipitation and flux tube erosion in Titan’s upper atmosphere
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DOI：
10.1016/j.icarus.2013.05.021
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发表时间：
2013-09
期刊：
影响因子：
3.2
通讯作者：
D. Snowden;R. Yelle;M. Galand;A. Coates;A. Wellbrock;G. Jones;P. Lavvas
中科院分区：
文献类型：
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作者：
D. Snowden;R. Yelle;M. Galand;A. Coates;A. Wellbrock;G. Jones;P. Lavvas
卡西尼号的数据显示，土卫六的大气层强烈地消耗了土星通量管中的电子含量，产生了被称为电子咬出的特征，这表明极光电子的通量随着时间的推移而减少。为了理解这一过程，我们开发了一个时间相关的双流模型，该模型使用了由泰坦等离子体相互作用的三维多流体模型计算的场线几何和漂移路径。该模型的边界条件解释了由于泰坦大气中电子的损失或产生，土星磁力线上的电子通量随时间的减少或增加。极光电子通量的变化取决于土星外磁层的电子弹跳周期；因此，我们也计算了沿几条克罗尼安场线的电子弹跳周期，考虑了磁镜像力和土星等离子体层的场向电势。我们使用时间相关的双流模型来计算极光电子通量的减少如何影响土卫六上层大气中的电子撞击电离和能量沉积速率。我们发现，随着时间的推移，进入土卫六大气层的高能电子（bbb50 eV）的通量大大减少，导致在~ 1300公里高度以下的电离和能量沉积率较小。最后，我们证明了由我们的计算产生的样品光谱图与CAPS-ELS数据是一致的。
Cassini dasta shows that Titan’s atmosphere strongly depletes the electron content in Saturn’s flux tubes, producing features known as electron bite-outs, which indicate that the flux of auroral electrons decreases over time. To understand this process we have developed a time-dependent two-stream model, which uses field line geometries and drift paths calculated by a three-dimensional multi-fluid model of Titan’s plasma interaction. The boundary conditions of the model account for the time-dependent reduction or increase in electron flux along Saturn’s magnetic field lines because of the loss or production of electrons in Titan’s atmosphere. The modification of the auroral electron flux depends on the electron bounce period in Saturn’s outer magnetosphere; therefore, we also calculate electron bounce periods along several Kronian field lines accounting for both the magnetic mirroring force and the field-aligned electric potential in Saturn’s plasma sheet. We use the time-dependent two-stream model to calculate how the reduction in the auroral electron flux affects electron impact ionization and energy deposition rates in Titan’s upper atmosphere. We find that the flux of higher energy (>50 eV) electrons entering Titan’s atmosphere is strongly reduced over time, resulting in smaller ionization and energy deposition rates below ∼1300 km altitude. Finally, we show that sample spectrograms produced from our calculations are consistent with CAPS-ELS data.