木星磁层物理研究

发布时间：2018-03-07 07:25

本文选题：木星　切入点：磁层　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：木星是太阳系中最大的行星,有着最快的自转角速度和最强的磁场,并与其周围的多颗卫星构成木星系。木星磁层在太阳风作用下包裹着木星,范围远超过伽俐略卫星的轨道,因此磁层活动不仅与太阳风相关,还受到磁层内卫星的影响。当磁层中物理过程产生高能粒子沿磁力线轰击木星电离层时就形成了木星极光,其按形态主要分为三类:明亮的主极光卵、卫星足迹和极区辐射。主极光卵目前认为与磁层共转破裂密切相关,卫星足迹直接反映了磁层与卫星的作用过程,而极区辐射变化较复杂,反映了中远磁尾多变的磁层活动。本文介绍了木星磁层的现有研究成果,扩展了具有离心力效应的木星稳态磁场模型,并在该磁场模型的基础上对木星磁层进行了初步研究。木星极光中极区辐射的具体形成过程颇有争议,我们提出一个简单且合理的极区辐射的发生原因一一中远磁尾处的磁力线扰动扭曲。Hill等人提出了木星磁层较差自转的角速度分布,本文认为在中远磁尾处角速度差异较大,相邻磁通量管受扰动易扭曲形成涡旋结构。通过具体的模拟分析显示,赤道面上大约54Rj(Rj=71,400km是木星半径)到59Rj的圆柱区域受扰动形成涡旋结构所引发的数十万安培电流注入到极区电离层,就可以形成大约半度大小的极区辐射,因此可以认为不同的扰动区域对应着极区辐射的不同亮斑,而亮度反映着扭曲的剧烈程度。木卫二的极光足迹是本文研究的关注点。木卫二在木星磁层中运动,与快速共转的木星磁场相互作用形成木星极光中木卫二的尾迹,此尾迹反映了连续扰动的磁通量管对木星电离层电流注入的过程。连接木卫二的磁通量管相对磁层而言尺度很小,因此可以应用细丝理论模拟木卫二运动引起的极光演化过程。模拟结果表明,未扰动的上游磁通量管经过大约720s的时间在木卫二拉伸作用下形成角度约为4°且相对于木卫二静止的拉伸磁通量管,当其脱离木卫二时在磁张力的作用下加速,在随后大约2160s的加速时间内,磁通量管的速度逐渐与背景磁力线接近。与此同时,磁通量管向木星电离层注入的电流也由9×105A逐渐衰减至0,以1/e初始电流处认为是可观测的木卫二尾迹限度,则木卫二的尾迹仅大约有一至两个经度,这与哈勃望远镜观测到的木卫二尾迹大小大致相同。从能量角度考虑,木卫二尾迹总的输送能量约为2.3×1013J,比木卫一输送的能量小一个量级,这是导致尾迹长度远小于木卫一的重要原因,同时也发现木卫二附近的压力凹槽对结果影响不大,可以忽略。木星磁层中的磁通量管在太阳风压力下和离心力作用下有复杂运动,在研究极区辐射的过程中我们进一步分析重联的磁通量的来源,同时还发现使用的磁场模型在低磁纬(Λ50°)磁场与观测基本符合,而高磁纬(Λ≥50)磁场与观测相比向外膨胀,特别是远磁尾区域膨胀更明显,不符合经验认识,需要优化其磁场位形。本文先利用熵参量来判定磁层的稳定性,熵参量PV5/3被广泛应用于分析磁层等离子体片中的输运问题,其中P是压力,V是单位磁通量管的体积,通过熵参量的分布和变化可以判断磁层的稳定性及揭示磁层中的动力学过程。对木星磁层的计算结果表明,磁层在55Rj内熵参量呈上升趋势,而之后有所下降,表明该模型在55Rj之外已经不稳定,这也证实了高磁纬的磁场位形需要优化。同时假想的磁场重联后的单位磁通量管的熵参量分布表明赤道面中远磁尾的磁场重联是由尾向输运的磁力线管拉伸断裂重联引起的。在随后的工作中为了优化磁场位形,我们在保持赤道面压力分布不变的条件下,采用坐标变换的方法改变磁矢势的分布,使中远磁尾磁场特别是高磁纬磁场向赤道面压缩。变换后的磁场位形与原模型相比,低磁纬位形基本不变,高磁纬则大幅压缩,更符合经验知识。
[Abstract]:Jupiter is the largest planet in the solar system, with the fastest rotation velocity and the strongest magnetic field, and many satellites around Jupiter and Jupiter form. The magnetic layer in the solar wind wrapped under Jupiter, far more than the range of Galileo satellite orbit, so the magnetosphere with the solar wind activity is not only related to it affected by the magnetic layer within the satellite. When the physical magnetic layer produced in the process of high-energy particle bombardment of Jupiter ionosphere along the magnetic field on the formation of the Jovian Aurora, according to its morphology is mainly divided into three categories: the main bright auroral and polar satellite footprint, radiation. The main auroral oval currently considered and magnetospheric corotation rupture closely related. The satellite footprint directly reflects the effect of magnetic layer and satellite process, while polar radiation change is complex, reflecting the changing of COSCO magnetotail magnetic layer. This paper introduces the existing research results of the jovian magnetosphere, extended with centrifugal force. Jupiter should the steady-state magnetic field model, and made a preliminary study on Jupiter's magnetosphere based on the magnetic field model. The specific region in the process of the formation of the Jovian auroral radiation controversial, we propose a simple and reasonable polar radiation causes one end of the magnetic disturbance COSCO magnetic distortion of.Hill et al. Proposed angular velocity Jupiter's magnetosphere differential rotation distribution, the larger magnetic tail angular velocity in COSCO between adjacent flux tubes disturbed easily distorted vortex structure. Through the simulation analysis shows that about 54Rj of the equatorial plane (Rj=71400km is the radius of Jupiter) disturbance caused by the formation of the vortex structure of hundreds of thousands of amperes of current injected into the polar region the ionosphere to the cylindrical region of 59Rj, polar radiation can form about half the size, so that the disturbance of different regions of the corresponding region of different radiation The light spot brightness reflects the severity of the distortion. Europa's aurora footprint is a focus of this study. Europa movement in Jupiter's magnetosphere, the formation of the Europa Jupiter in the aurora wake and fast interaction were transferred to Jupiter's magnetic field, the wake reflects the process of implantation on Jupiter ionospheric current flux continuous disturbance the magnetic flux tube. The tube connecting Europa relative magnetic layer scale is very small, so it can be used fine theoretical simulation movement caused by the evolution of Aurora Europa. Simulation results show that the upstream flux of undisturbed tube after about 720s hours in Europa under tension forming angle of approximately 4 degrees relative to the tensile and magnetic flux Ganymede two stationary tube, when the detachment in Europa magnetic tension under the effect of acceleration, then about 2160s acceleration time, magnetic flux tube speed gradually and magnetic background Close to the line. At the same time, the current magnetic flux tube into the ionosphere to Jupiter from 9 * 105A to 1/e gradually decreases to 0, the initial current that is observable wake limit Europa, Europa is wake only about one or two longitude, and the size of Europa wake Harbert telescope observed roughly the same. Considering from the perspective of energy, the total energy transfer from Europa wake is about 2.3 * 1013J, bimu Wei of the energy delivered one order, which is an important cause of the wake length is far less than IO, also found little effect of pressure on the groove near Europa can be ignored. The magnetic flux in the magnetic layer of the tube with Jupiter the complex motion in the solar wind pressure and centrifugal force, in the process of polar radiation we further analyze the sources of heavy magnetic flux coupling, but also found that the use of the model in low magnetic field Weft (a 50 DEG) magnetic field accorded with observation, and high latitude (lambda = 50) compared with the observed magnetic field expansion, especially in the distant magnetotail region expansion is more obvious, with experience, needs to optimize the configuration of the magnetic field. This paper first use of entropy to determine the stability of the magnetic layer, the entropy parameter PV5/3 is widely used in the analysis of transport problem in the plasma sheet magnetic layer, where P is the pressure, V is the unit of magnetic flux tube volume, through the distribution and change of entropy can determine the stability of the magnetic layer and reveal the dynamic process in the magnetosphere. The magnetosphere of Jupiter on the calculation results show that the magnetic layer in 55Rj entropy parameter increased, and then decreased, showed that the model in 55Rj is not stable, which also confirmed the high latitude magnetic field configuration needs to be optimized. At the same time entropy parameters distribution of imaginary magnetic unit magnetic flux contact after the measuring tube shows that the equatorial plane of COSCO The magnetotail magnetic reconnection is from the tail to the transport of magnetic flux tube tensile fracture reconnection. In subsequent work in order to optimize the configuration of the magnetic field, we keep the equatorial surface pressure distribution under the same conditions, using the coordinate transformation method, change the distribution of the magnetic vector potential, the long tail magnetic especially high latitude magnetic field to the equatorial magnetic field compression. After transformation compared with the original model, the low magnetic latitude position unchanged, high latitude is substantially reduced, more in line with the experience and knowledge.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P185.4

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