Physics of the Ion Composition Boundary: a comparative 3-D hybrid simulation study of Mars and Titan
Physics of the Ion Composition Boundary: a comparative 3-D hybrid simulation study of Mars and Titan
复制标题
离子成分边界物理学：火星和土卫六的比较 3D 混合模拟研究
DOI：
10.5194/angeo-25-99-2007
复制
发表时间：
2007
影响因子：
1.9
通讯作者：
U. Motschmann
中科院分区：
文献类型：
--
作者：
S. Simon;A. Boesswetter;T. Bagdonat;U. Motschmann
抽象的。火星和土卫六的等离子体环境已经通过一个3-D混合模拟代码进行了研究，将电子视为无质量的电荷中和流体，而离子动力学则采用动力学方法。由于火星和土卫六都没有明显的内部磁场，因此上游的等离子体流直接与行星电离层相互作用。的相互作用区域的特征的确定作为一个函数的alfvenic，声波和磁声马赫数的撞击等离子体。对于火星与太阳风的相互作用，以及土卫六在太阳风动压高的时候位于土星磁层之外的情况，所有三个马赫数都大于1。在这种情况下，相互作用产生了所谓的离子成分边界，将电离层等离子体与环境流分离，并且相对于对流电场的方向高度不对称。通过分析作用在电离层和周围等离子体粒子上的洛伦兹力，解释了这些特征的形成。土卫六的等离子体环境是高度可变的，允许三个马赫数的各种不同组合。因此，在某些情况下，离子成分边界可能消失。相关的物理机制被说明为在上游等离子体流的马赫数的函数。
Abstract. The plasma environments of Mars and Titan have been studied by means of a 3-D hybrid simulation code, treating the electrons as a massless, charge-neutralizing fluid, whereas ion dynamics are covered by a kinetic approach. As neither Mars nor Titan possesses a significant intrinsic magnetic field, the upstream plasma flow interacts directly with the planetary ionosphere. The characteristic features of the interaction region are determined as a function of the alfvenic, sonic and magnetosonic Mach number of the impinging plasma. For the Martian interaction with the solar wind as well as for the case of Titan being located outside Saturn's magnetosphere in times of high solar wind dynamic pressure, all three Mach numbers are larger than 1. In such a scenario, the interaction gives rise to a so-called Ion Composition Boundary, separating the ionospheric plasma from the ambient flow and being highly asymmetric with respect to the direction of the convective electric field. The formation of these features is explained by analyzing the Lorentz forces acting on ionospheric and ambient plasma particles. Titan's plasma environment is highly variable and allows various different combinations of the three Mach numbers. Therefore, the Ion Composition Boundary may vanish under certain circumstances. The relevant physical mechanism is illustrated as a function of the Mach numbers in the upstream plasma flow.