Three-dimensional multispecies hybrid simulation of Titan's highly variable plasma environment
Three-dimensional multispecies hybrid simulation of Titan's highly variable plasma environment
复制标题
土卫六高度多变的等离子体环境的三维多物种混合模拟
DOI：
10.5194/angeo-25-117-2007
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发表时间：
2007
影响因子：
1.9
通讯作者：
J. Schuele
中科院分区：
文献类型：
--
作者：
S. Simon;A. Boesswetter;T. Bagdonat;U. Motschmann;J. Schuele
摘要。土卫六电离层与土星磁层等离子体流之间的相互作用已经通过三维（3-D）混合模拟代码进行了研究。在混合模型中，电子形成无质量的电荷中和流体，而保留了完全动力学方法来描述离子动力学。该模型包括多达三种电离层离子和两种磁层离子。这种相互作用产生了一个明显的磁垂模式和一个电离层尾巴，它与对流电场的方向高度不对称。由于离子陀螺半径与离子质量的关系，不同质量的离子在尾区出现空间分散。因此，土卫六的电离层尾巴可以被认为是一个质谱仪，可以区分不同质量的离子种类。通过将模拟结果与拾取过程的简单解析测试粒子模型的结果进行比较，强调了这种效应的动力学性质。此外，这些结果清楚地说明了考虑土卫六附近磁层等离子体流的多物种性质的必要性。一方面，重磁层粒子，如原子氮或原子氧，其流动模式只经历轻微的改变。另一方面，轻的电离层离子，例如氢原子，在障碍物周围明显偏转，产生垂直于流动方向的磁垂模式的加宽。模拟结果清楚地表明，这种相互作用过程的性质，特别是在土卫六附近形成明显的等离子体边界，对磁层离子的温度和土卫六日侧电离层相对于旋转磁层等离子体流的方向极为敏感。
Abstract. The interaction between Titan's ionosphere and the Saturnian magnetospheric plasma flow has been studied by means of a three-dimensional (3-D) hybrid simulation code. In the hybrid model, the electrons form a mass-less, charge-neutralizing fluid, whereas a completely kinetic approach is retained to describe ion dynamics. The model includes up to three ionospheric and two magnetospheric ion species. The interaction gives rise to a pronounced magnetic draping pattern and an ionospheric tail that is highly asymmetric with respect to the direction of the convective electric field. Due to the dependence of the ion gyroradii on the ion mass, ions of different masses become spatially dispersed in the tail region. Therefore, Titan's ionospheric tail may be considered a mass-spectrometer, allowing to distinguish between ion species of different masses. The kinetic nature of this effect is emphasized by comparing the simulation with the results obtained from a simple analytical test-particle model of the pick-up process. Besides, the results clearly illustrate the necessity of taking into account the multi-species nature of the magnetospheric plasma flow in the vicinity of Titan. On the one hand, heavy magnetospheric particles, such as atomic Nitrogen or Oxygen, experience only a slight modification of their flow pattern. On the other hand, light ionospheric ions, e.g. atomic Hydrogen, are clearly deflected around the obstacle, yielding a widening of the magnetic draping pattern perpendicular to the flow direction. The simulation results clearly indicate that the nature of this interaction process, especially the formation of sharply pronounced plasma boundaries in the vicinity of Titan, is extremely sensitive to both the temperature of the magnetospheric ions and the orientation of Titan's dayside ionosphere with respect to the corotating magnetospheric plasma flow.