【作者】 童冬生；

【导师】 陈出新；

【作者基本信息】 中国科学技术大学 ， 空间物理， 2011， 博士

【摘要】 在太阳系八大行星中,除金星和火星之外,其它行星都有比较强的内禀磁场。鉴于各个行星自身的差异性,特别是它们的磁场拓扑结构,因而它们与太阳风作用的性质有所不同,各自形成的磁层结构以及产生的磁层现象也不尽相同。火星被认为是太阳系中自然环境最接近地球的行星,因此越来越为人类所关注。对火星磁场的探测与研究已经成为空间物理领域里的热门课题之一。本文利用火星具有电离层而无内禀磁场的特点以及它与太阳风作用的性质,从电流的角度出发,建立火星感应磁场模型,对火星感应磁场产生的原因、分布情况进行研究。同时,根据探测器所观测到的火星极光图片,建立极光区地壳磁场模型,得到了磁力线拓扑结构并且讨论了磁异常的成因。本文的主要工作以及得到的结果概括如下:由于火星没有显著的内禀磁场,它与太阳风作用的方式与地球有很大的差异。太阳风直接与火星电离层、大气层发生相互作用,导致了火星电离层上出现感应电流。在第二章中,根据卫星所观测到的火星磁场分布特征以及电流始终包络磁力线这一特性,构建了火星磁层电流体系模型。在模型中,火星磁层顶电流,电离层电流以及磁尾中性片电流构成了火星磁层电流体系。根据电流连续性的条件,这三种电流满足一定的关系:磁层顶上通过的总电流是电离层上通过的总电流与磁尾中性片通过的总电流之和。本文分别讨论了火星磁层电流体系分布的二维近似模型和三维分布模型。第三章以火星磁层电流体系模型为基础,分别构建了火星感应磁场二维近似模型和三维模型。在模型中,火星磁层顶电流,电离层电流以及磁尾中性片电流产生的磁场与太阳风磁场一起构成了火星周围的磁场分布。根据毕奥-萨伐尔定理和利用磁力线跟踪程序,得到了火星赤道面以及与赤道面平行的其它平面内的磁场分布。计算结果表明,根据模型得到的磁场分布与卫星观测到的结果以及他人研究结果符合的较好。火星周围的磁场分布与具有内禀磁场的行星不同,其磁力线披挂在火星周围,在磁尾形成一个开放的结构。同时计算结果还表明,不同平面内磁力线拓扑结构既有类似的地方,又存在较大的差异性。与赤道面平行且越近的平面内,磁力线的“拖拽”程度越明显,这主要由于火星电离层对不同的区域内行星际磁场的阻碍程度不同。与具有较强内禀磁场的行星两极上出现的极光不同,火星极光主要发生在南半球地壳磁场异常的区域,并且极光分布特征与其它行星上的极光也有所区别。第四章在“火星全球勘探者”和“火星快车”的最近观测结果基础上,从等效电流的角度出发,建立了火星极光区地壳磁场模型,得到了火星地壳磁异常区的磁场拓扑结构。基于极光发生于磁力线汇聚的地方,利用模型得到的磁场拓扑结构,能够复原出所观测到的火星极光图像。同时,根据火星极光弧的宽度比较窄这一显著分布特征,本文对火星地壳磁异常的起因进行了讨论。更多还原

【Abstract】 Among eight planets in the solar system, the other planets have relatively strong intrinsic magnetic field except Venus and Mars. In view of their differences among all planets, especially their magnetic field topologies, the characteristics of interaction between planets and the solar wind are not the same and their magnetospheric structures and phenomena produced through interaction with solar wind are not the same. Mars among planets in the solar system is considered to be the most closest to earth in natural environment, so the human being are more and more concerned for Mars. Exploration and research of Martian magnetic field has become a hot topic in the field of space physics.In this thesis, based on facts that there is an ionosphere above the solid Mars but there is no intrinsic magnetic field inside the solid Mars, and also the characteristics of interaction between the solar wind and Martian ionosphere, a model of Martian induced magnetic field is proposed from the perspective of the current, and causes and the distribution of Martian induced magnetic field are studied. In addition, according to Martian aurora picture observed through spacecraft, a model of crustal magnetic field on Martian aurora zone is established, and topology of magnetic field lines is obtained, and the causes of magnetic anomalies are discussed. The main work and the results obtained are summarized as follows:Since there is no obvious intrinsic magnetic field at Mars, the characteristics of interaction between the solar wind and Mars are different from that of earth. The solar wind interacts directly with the Martian ionosphere and atmosphere, resulting on the appearance of the induced current on ionosphere. In the second chapter, a model of currents in the Martian magnetosphere is constructed based on the distribution of Martian magnetic field gained through satellite observations and the characteristics that the current always envelopes the magnetic field lines. In the model, the magnetopause current, the ionospheric current and the current sheet in magnetotail form the current system in Martian magnetosphere. According to the continuity of the current, these currents satisfy the relation that the total current in the Martian magnetopause is equal to the summation of the total current in the Martian ionosphere and the total current in the Martian magnetotail. This thesis discusses two-dimensional approximation model and three-dimensional distribution model of the current system in Martian magnetosphere respectively.In the third chapter, we construct two-dimensional approximation model and three-dimensional model of Martian induced magnetic field based on the current system model of Martian magnetosphere. In the model, Superposition of the magnetic field generated by these currents and solar wind magnetic field constitutes the distribution of magnetic field around Mars. According to Biot-Savart theorem, we get the distribution of magnetic field in Martian equatorial plane and the other plane parallel to equatorial plane using the program of tracing magnetic field lines. The results show the magnetic field distribution obtained by the model is consistent with observational results through satellite and those gained by others. Distribution of magnetic field around Mars is different from that of those planets having intrinsic magnetic field, and the magnetic field lines drape around Mars, forming an open structure in the magnetotail. Results also show that the topologies of magnetic field in different planes have both similarities and differences. In the plane parallel and closer to equatorial plane, the magnetic field lines drag more obviously, mainly because Martian ionosphere hinders interplanetary magnetic field at different extents in the different regions.Differing from auroras occurring on poles of planets with a strong intrinsic magnetic field, the Martian aurora occurs mainly in the region of crustal magnetic anomalies in southern hemisphere, and the distribution of the aurora differs from that of other planets. In the fourth chapter, from the equivalent currents point of view, we establish the model of the Martian crustal magnetic field on aurora zone, and gain the topology of crustal magnetic anomalies. Based on the fact that aurora occurs where the magnetic field lines converge, we can recover the Martian aurora morphology observed by Mars Global Surveyor and Mars Express through the topology of magnetic field according to the model. In addition, according to the obvious feature of the narrow width about Martian aurora arcs, the causes of the Martian crustal magnetic anomalies are discussed in this thesis.更多还原