行星际磁云中等离子体旋转运动的机制研究

发布时间：2018-03-04 10:38

本文选题：日冕物质抛射　切入点：磁云　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】：日冕物质抛射(coronal mass ejections,CMEs)是太阳大气中最剧烈、太阳系中尺度最大的活动现象,它们的爆发可以在短时间内使日冕抛射的携带大量磁场的物质进入行星际空间。磁云作为日冕物质抛射在行星际中的对应物,大量研究证明它的大的行星际磁场的南向分量为造成大的地磁暴的主要原因,因此,磁云作为灾害性空间天气的主要驱动者,它的行星际动力学演化一直以来都是我们研究的重点。然而,长期以来人们更关注磁云的整体动力学演化过程,对于磁云内部等离子体的运动研究较少。由于磁云的大尺度结构特征,局地卫星仅能帮助我们了解磁云内等离子体运动的局部特征,并且,由于磁云内磁场湍流的影响,可能有些运动被大的涨落所掩盖。最近Wang etal.(2015)发现大量磁云内等离子体具有旋转运动,即在运动的磁云坐标系中有绕轴的速度分量,然而,造成这种运动的原因是什么?这些原因与外部环境有什么样的关系?在本论文中,我们将从引起磁云内等离子体旋转运动的原因和该原因与外部环境参数之间的关系来对磁云内等离子体的旋转运动进行细致深入地研究,希望能够对磁云从日面到行星际的动力学演化提供进一步的理解。1、磁云内等离子体旋转运动产生的主要原因Wang et al.(2015)发现大量磁云内等离子体具有旋转运动,然而对于这种运动产生的原因仅仅给出了三种推测:(1)与局地太阳风的相互作用产生;(2)日冕物质抛射在行星际传播的过程中由内部磁能转化成动能包含了旋转分量;(3)日冕物质抛射在日面上爆发时产生,并且由于角动量守恒而携带到1AU处。为了研究磁云内等离子体旋转运动产生的原因,我们采用多卫星观测的方法,利用STEREO-A、Wind、STEREO-B三颗卫星所观测到的同一个磁云,借助速度修正的柱型对称线性无力场模型对三颗卫星上的磁云进行了重构,在磁云坐标系中研究了与磁云轴向垂直的平面内等离子体的速度分量。我们发现Wind和STEREO-B卫星上磁云内等离子体有明显的旋转运动,而STEREO-A卫星上磁云内等离子体没有明显的旋转运动,三颗卫星上同一个磁云内不同的等离子体旋转运动表明引起磁云内等离子体旋转运动的原因可能为局地的因素。进一步对磁云内等离子体及周围太阳风中等离子体旋转速度的研究,我们发现磁云前后边界处磁云内等离子体的旋转方向分别与周围太阳风中等离子体的旋转方向相一致,并且当磁云前后边界外太阳风等离子体的旋转速度方向一致时,磁云内等离子体有明显的旋转运动,而当前后边界外太阳风等离子体的旋转速度方向不一致时,磁云内没有明显的旋转运动,这个结果表明磁云与周围太阳风的相互作用应该是引起磁云内等离子体旋转运动的可能原因。同时,我们还发现太阳风等离子体与磁云内等离子体旋转速度数值之间呈粗略的正相关,并且除了 STEREO-B卫星,其它卫星上太阳风等离子体的旋转速度粗略地大于磁云内等离子体的旋转速度,这是粘性引起等离子体旋转运动的特征。因此,磁云与局地太阳风通过粘性相互作用应该是引起磁云内等离子体旋转运动的一种原因。2、粘性在引起磁云内等离子体旋转运动中所起的作用粘性是太阳风的本质特性,前人的研究已经表明粘性作为空气动力学中的拖拽力对大尺度结构的动力学过程产生了重要的影响,并且在日冕物质抛射到达地球的预测模型中得到了很好的证明。我们试图研究粘性在造成磁云内等离子体旋转运动中所起的作用。若太阳风中粘性为造成磁云内等离子体旋转运动的原因,那么等离子体的旋转速度从磁云内到外应该呈增加趋势。我们从93个磁云前后边界处的穿越事件(186)中筛选出了 35个满足磁云内等离子体旋转速度方向与周围太阳风速度方向一致且旋转速度绝对值大于或等于10 km s-1的穿越事件,在磁云边界内外每30分钟得到等离子体旋转速度的平均值,统计研究发现磁云内等离子体的旋转速度与周围太阳风等离子体的旋转速度两两之间呈现很高的相关性,并且两者之间线性拟合斜率表明周围太阳风等离子体的旋转速度大于磁云内等离子体的旋转速度,且从磁云内到外旋转速度呈非单调性增加趋势,这些特征表明粘性确实是造成磁云内等离子体旋转运动的一个原因,但是,由于这些事件仅占总事件的比例为19%,因此,太阳风中粘性在造成磁云内等离子体旋转运动中所起的作用是弱的。那么,粘性与太阳风的参数例如密度、温度和磁场的湍动强度之间的相关性如何呢?我们又仔细检查了所有磁云事件前后边界处等离子体旋转速度的变化,找到那些能较好地展现太阳风中粘性造成磁云内等离子体旋转运动的9个事件,得到了太阳风中粘性与磁云内和太阳风等离子体参数之间的关系,发现粘性与密度之间呈现强的负相关,与磁场的湍动强度之间呈现弱的负相关,而与温度之间没有明显的相关性。这一背后的物理机制值得我们深入研究。
[Abstract]:Coronal mass ejections (coronal mass, ejections, CMEs) is the most intense activity in the atmosphere of the sun, the solar system's largest scale phenomenon, they broke out in a short period of time can make the magnetic field of coronal mass ejections to carry large amounts of material into the interplanetary magnetic cloud. As a coronal mass ejection counterpart of the interplanetary, a lot of research proof of the main reasons, caused major geomagnetic storms for the large southward component of the interplanetary magnetic field of the magnetic cloud as it so disastrous space weather the main drivers of its interplanetary dynamics evolution has always been the focus of our research. However, for a long time people pay more attention to the evolution of the overall dynamics of the magnetic cloud the movement of the plasma within the magnetic cloud for less. Because of the large scale structure characteristics of magnetic clouds, local satellite can only help us understand the local magnetic cloud plasma movement characteristics, and And, because of the influence of magnetic field due to turbulence, there may be some movement covered by large fluctuations. Recently, Wang etal. (2015) found that a large number of magnetic cloud plasma with rotary motion, namely weight, speed around the axis movement in the magnetic cloud coordinate system, however, the cause of this movement is what the reasons are? What kind of relationship with the external environment? In this thesis, we will from the relationship between the cause of magnetic rotary motion and the plasma cloud reason and the external environment of the parameters of the rotary motion of the magnetic plasma cloud detailed in-depth study, hoping to provide a further understanding of.1 from the surface to the magnetic cloud on line the main reason for the dynamic evolution of interplanetary magnetic cloud, plasma rotation generated by Wang (2015) et al. found that a large number of magnetic cloud plasma with rotary motion, but for this movement causes For given only three kinds of speculation: (1) interact with the local solar wind; (2) the process of CMES in the interplanetary propagation by internal energy into kinetic energy contains a rotating component; (3) to produce CMEs broke out in the on surface, and the angular momentum conservation carry to 1AU. In order to study the magnetic cloud plasma rotation motion, we adopt the method of multi satellite observations by STEREO-A, Wind, with a magnetic cloud STEREO-B three satellites observed, with the column type velocity correction of symmetric linear force free field model for the reconstruction of the magnetic cloud three satellites in the magnetic cloud coordinates on the velocity component of plasma and the plane vertical to the axial direction of the magnetic cloud. We found that Wind and STEREO-B satellite magnetic cloud plasma rotating motion obviously, and the STEREO-A satellite magnetic plasma cloud The body does not rotate significantly, plasma rotation of three satellites on the same magnetic cloud that causes different magnetic cloud plasma rotary motion may be local factors. Further research on plasma and plasma magnetic cloud around the solar wind speed of the rotary body, we found that the direction of rotation of the boundary magnetic plasma cloud the magnetic cloud respectively before and after consistent with the direction of rotation around the solar wind plasma, and when the rotational speed of the magnetic cloud and direction of the solar wind plasma boundary line, magnetic cloud plasma rotating motion obviously, and the direction of rotation speed when the solar wind plasma before and after the boundary is not consistent, no obvious rotational movement of magnetic cloud the results show that the interaction between magnetic cloud and solar wind around the clouds should be caused by magnetic plasma rotation movement can be Can cause. At the same time, we also found a positive correlation between the rough numerical solar wind plasma and magnetic cloud plasma rotation speed, and in addition to the STEREO-B satellite, the other satellite solar wind plasma rotation speed is roughly larger than the magnetic cloud plasma rotation speed, which is characteristic of plasma rotation caused by viscosity. Therefore, magnetic cloud with the local solar wind through the viscous interaction should be caused by a.2 magnetic cloud plasma rotary motion, viscous nature of the solar wind in the viscous effect induced by magnetic cloud plasma rotation movement, previous studies have shown that viscous as aerodynamic drag force in the dynamic process of the large scale structure of production an important influence, and reach the prediction model in the earth has been well demonstrated in CMEs. We try In the chart of the viscosity caused by magnetic rotation effect of plasma cloud. If the viscosity in the solar wind to cause magnetic cloud plasma rotation, then the rotation velocity of the plasma from the magnetic cloud to the outside should be increased. We from 93 before and after the magnetic cloud boundary crossing events (186) screening the 35 meet the magnetic direction of rotation speed and the plasma cloud around the solar wind velocity in the same direction and the rotation speed of the absolute value is greater than or equal to 10 km S-1 through an event, in the magnetic cloud boundary inside and outside every 30 minutes to get the average value of the plasma rotation velocity, the statistical study found that presentation of a very high correlation between the magnetic rotation speed of the plasma cloud with the surrounding solar wind plasma rotation speed 22, and between the two linear fitting slope shows that the rotation speed around the solar wind plasma is larger than the magnetic The rotation speed of the plasma cloud, and the cloud to the outside from the magnetic rotation speed increased non monotonic, these features indicate that the viscosity is indeed a cause, but the rotational motion of the plasma magnetic cloud, because these events only accounted for the total proportion of events was 19%, therefore, the solar wind is weak in the viscous since the magnetic rotation effect of plasma cloud. Then, with the solar wind viscous parameters such as density, how the correlation between temperature and magnetic turbulence intensity? We also examined the change of boundary plasma rotation speed before and after all the magnetic cloud event, find those who can better show the viscosity in the solar wind cause 9 events of magnetic rotary movement of the plasma cloud, the relationship between the solar wind and the solar wind viscous and magnetic cloud of plasma parameters is found between viscosity and density Strong negative correlation is weakly negatively correlated with the turbulence intensity of magnetic field, but has no obvious correlation with temperature. The physical mechanism behind this is worth further study.

【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】：P353

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