外加剪切流下三维磁重联动力学过程的研究

发布时间：2018-03-19 19:53

本文选题：磁场重联　切入点：剪切流　出处：《浙江大学》2016年博士论文　论文类型：学位论文

【摘要】：磁场重联是一种将磁能转化为动能和热能的有效机制,磁场重联发生时电流片两侧之间的质量、动量、能量可以进行交换。磁场重联被认为是解释在空间和实验室等磁化离子体中的许多爆发性物理现象的有效机制,例如太阳耀斑、地球磁层中的亚暴以及托克马克里的锯齿振荡等现象。为了使磁场重联可以解释一些观测现象,其时间尺度是一个很重要的判据,即重联的时间尺度要比扩散的时间尺度快很多。剪切流不论在空间等离子体还是实验室等离子体中都广泛存在,所以有必要去研究等离子体中剪切流对磁场重联过程的影响。我们应用数值模拟的方法采用可压缩电阻磁流体力学模型和可压缩Hall磁流体力学模型。模拟中采用了两种不同的初始磁场位形,即三维平板位形和偶极场位形,来研究三维磁场重联的动力学过程。首先,我们采用磁场的平板位形,其电流片宽度随y变化。我们发现磁场重联速度大幅度减弱,外加剪切流后,所产生的激波强度也相对减弱,在不同y平面内尽管电流片的形态即重联过程十分不同,可在重联入流区所形成的激波的结构却十分的一致,无论是所处的位置还是强度都极其相似。接着,我们采用地球真实磁场结构类似的偶极场位形来研究太阳风和地球磁层相互作用中的磁场重联过程。当太阳风携带的行星际磁场分别为南向和北向时,所得结果与一些观测现象一致。加入Hall效应之后,出现的非对称Hall四极场随着离子惯性长度谚变大强度变强分布范围更广。当太阳风携带的等离子体流存在z方向的流速vswz时,向阳面磁层顶的磁场重联发生的区域基本没有改变,磁场重联速度随着vswz的增加而加快。地球磁尾区域会发生很大的偏转,磁尾电流片偏转的角度与vswz呈线性增长关系。当太阳风携带的BIMF存在y分量时,我们第一次通过三维全球性磁流体动力学模型发现在地球的磁尾区域附近出现了磁场By。当θ=30°(BIMFy=BIMFsinθ)时,地球磁尾附近出现的磁场岛的最大值主要分布在磁尾电流片区域且大小已经超过BIMFy,BIMFy的存在还可以促进向阳面磁层顶的磁场重联过程。当θ变大时,向阳面磁层顶的磁场重联过程减弱,地球的磁尾区域的磁场By减弱且分布结构发生了很大的变化。这些结果详细讨论了三维磁场重联动力学过程,可能可以用来解释一些卫星观测现象。
[Abstract]:Magnetic reconnection is an effective mechanism for converting magnetic energy into kinetic energy and heat energy. Energy can be exchanged. Magnetic reconnection is considered to be an effective mechanism for explaining many explosive physical phenomena in magnetized ion bodies such as space and laboratories, such as solar flares. Substorms in the earth's magnetosphere and sawtooth oscillations in Tokkkari's magnetosphere. In order for magnetic field reconnection to explain some observational phenomena, its time scale is a very important criterion. That is, the time scale of reconnection is much faster than that of diffusion. Shear flow is widespread in both space plasma and laboratory plasma. Therefore, it is necessary to study the influence of shear flow in plasma on the magnetic reconnection process. The compressible resistance magnetohydrodynamic model and the compressible Hall magnetohydrodynamic model are used in the numerical simulation. Two different initial magnetic field configurations, That is, three-dimensional plate configuration and dipole field configuration to study the dynamic process of three-dimensional magnetic reconnection. Firstly, we adopt the plate configuration of magnetic field, and the current sheet width changes with y. We find that the magnetic reconnection velocity is greatly weakened. The intensity of shock wave produced by the applied shear flow is also relatively weak. In different y plane, although the shape of the current sheet is very different, that is, the reconnection process, the structure of the shock wave formed in the reentrant flow region is very consistent. The position and intensity are very similar. Then, The reconnection of the magnetic field in the interaction between the solar wind and the earth's magnetosphere is studied by using a similar dipolar configuration of the real magnetic field of the earth. When the interplanetary magnetic field carried by the solar wind is south and north respectively, The results are consistent with some observational phenomena. With the addition of the Hall effect, the intensity distribution of the asymmetric Hall quadrupole field increases with the ion inertial length saying. When the plasma current carried by the solar wind exists in the z direction of velocity vswz, The magnetic reconnection to the positive magnetopause is basically unchanged, and the magnetic reconnection speeds up with the increase of vswz. The angle of deflection of the magnetic tail current sheet is linearly related to the vswz. When the BIMF carried by the solar wind has y component, we find for the first time that the magnetic field Bynear the magnetic tail region of the earth appears in the vicinity of the earth's magnetohydrodynamic model through the 3D global magnetohydrodynamic model. The maximum value of the magnetic island near the earth's magnetic tail is mainly distributed in the region of the current sheet of the magnetic tail and the existence of the BIMFyBIMFy can also promote the magnetic reconnection to the positive magnetopause. The magnetic reconnection to the positive magnetopause is weakened, and the magnetic field by in the magnetic tail region of the earth is weakened and the distribution structure is greatly changed. These results discuss in detail the dynamic process of the three-dimensional magnetic reconnection. It may be used to explain some satellite observations.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O361.3

【相似文献】