全球日冕演化的自适应数据驱动模式和日冕磁场外推

发布时间：2018-01-15 21:19

本文关键词：全球日冕演化的自适应数据驱动模式和日冕磁场外推　出处：《中国科学院研究生院（空间科学与应用研究中心）》2011年博士论文　论文类型：学位论文

【摘要】：太阳日冕是空间天气事件发生的上层区,其中丰富的结构及其演化是空间物理研究的重要内容.数据驱动的日冕模拟,是指在日冕底边界上连续时序地输入观测数据(如磁场)来驱动日冕数值模式,以模拟日冕真实的动力学演化;是研究日冕大尺度结构演变和太阳爆发活动的有力工具.本文侧重于计算技术层面,基于时空守恒数值格式(CESE)和自适应网格方法(AMR),开发了一个新型的日冕太阳风自适应模式;并联合光球磁流输运模型,建立了首个由时变光球磁图驱动的全球日冕动态演化MHD模式. 作用一种新型高效的数值格式, CESE方法已成功地应用于多种空间物理问题的模拟研究.基于一般曲线坐标理论,本文通过把物理空间下的主控方程变换到计算空间并保持守恒形式,首先将CESE格式推广到了一般曲线坐标下.然后借助于并行自适应软件包PARAMESH,并克服了CESE格式和自适应网格系统的各种不兼容性(如时空交错问题,库朗数敏感问题等),将一般曲线CESE格式成功实现于块状自适应网格上,建立了一个MHD数值模拟的新方法AMR-CESE-MHD. 为精确刻画日冕底部球型边界面而不引入两极奇点问题,采用一种基于球坐标的重叠型网格(Yin-Yang网格)以克服其他网格系统的各种弱点,并利用高精度的插值保证重叠边界信息相互无障碍的传递.自适应的日冕太阳风模型即建立于该网格系统和AMR-CESE-MHD方法上.时变自洽的底面边界条件基于投影特征线方法和一个描述光球磁图演化的模型表面磁流输运(SFT)模型.SFT模型采用观测的综合磁图作为输入,能够很好的再现长达几个月的日面磁流的变化,而且避免了直接采用观测磁图而导致的不兼容性.通过模拟长达三个太阳自转周的动态演化并与多观测日冕图像进行比较,展示了该日冕动态模式模拟全球日冕基本结构如冕流,冕洞位置和活动区磁场及其演化的能力. 此外,由于日冕的三维磁场尚不能直接观测.作为一种替代办法,磁场外推(重构)也是研究日冕活动的一种重要方法.通过考察外推磁场的拓扑结构,可以发掘导致太阳爆发活动的不稳定磁场位形.本文针对于重构日冕磁场的松弛法,提出了一种新的实现方式.不同于以往的仅求解无力场模型的办法,我们采用全磁流体模型,并利用简洁而高效的CESE格式来求解.光球(底面)边界条件类似于挤压松弛(stress-and-relax)方法,使初始的势场分布逐渐逼近于观测的矢量磁图.计算区域的其他人工边界全部采用基于投影特征线方法的无反射边界条件.我们将这个方法外推了无力场的两个经典解析解.结果证明了方法的有效性并且细致的分析发现和目前国际上最好的方法相当.
[Abstract]:The solar corona is the upper layer of space weather events, in which rich structures and their evolution are important contents of space physics research. It refers to the continuous input of observational data (such as magnetic field) at the bottom boundary of the corona to drive the numerical model of the corona to simulate the real dynamic evolution of the corona. It is a powerful tool for studying the evolution of the coronal large-scale structure and solar burst. This paper focuses on the computational techniques, based on the time-space conservation numerical scheme (CESE) and adaptive grid method (AMRs). A new adaptive model of coronal solar wind is developed. Combined with the optical sphere flux transport model, the first global coronal dynamic evolution MHD model driven by a time-varying optical sphere magnetic map is established. As a new and efficient numerical scheme, the CESE method has been successfully applied to the simulation of various spatial physics problems based on the general curvilinear coordinate theory. In this paper, the main control equation in the physical space is transformed into the computational space and the conservation form is maintained. Firstly, the CESE scheme is extended to the general curvilinear coordinates, and then the parallel adaptive software package PARAMESH is used. It overcomes all kinds of incompatibilities of CESE scheme and adaptive grid system, such as time-space interleaving problem, Current number sensitive problem and so on. The general curve CESE scheme is successfully implemented on the block adaptive grid. A new MHD numerical simulation method, AMR-CESE-MHD, is established. In order to accurately characterize the spherical boundary surface at the bottom of the corona without introducing the bipolar singularities, an overlapping meshes based on spherical coordinates (Yin-Yang mesh) are used to overcome the weaknesses of other grid systems. High precision interpolation is also used to ensure the smooth transmission of overlapping boundary information. Adaptive Corona. The solar wind model is based on the grid system and the AMR-CESE-MHD method. The time-varying self-consistent bottom boundary condition is based on the projection feature line method and a model to describe the evolution of the optical sphere magnetic map. Surface magnetic current transport (. The SFT model SFT model uses the observed synthetic magnetic map as the input. It can reproduce the variation of the helioid flux for several months. In addition, the incompatibility caused by the direct use of observational magnetic maps is avoided. The dynamic evolution of three solar rotation cycles is simulated and compared with the multi-observational coronal images. The ability of the dynamic model to simulate the global coronal basic structures such as coronal current, coronal hole position and magnetic field in the active region and its evolution are demonstrated. In addition, because the three-dimensional magnetic field of the coronal can not be observed directly, as an alternative method, the extrapolation of magnetic field (reconstruction) is also an important method to study the coronal activity. The topological structure of the extrapolation magnetic field is investigated. The unstable magnetic field configuration which leads to the solar burst activity can be discovered. In this paper, a new realization method is proposed for the relaxation method of the reconstructed coronal magnetic field, which is different from the previous method which only solves the model of the force field. We use a magnetic fluid model and a simple and efficient CESE scheme to solve the problem. The boundary conditions of the optical sphere (bottom) are similar to those of the squeeze relaxation stress-and-relaxation method. The distribution of the initial potential field is gradually approaching to the observed vector magnetic map. The other artificial boundaries of the computational region are all based on the non-reflective boundary conditions based on the projection characteristic line method. We extrapolate two of the two fields of the force field by using this method. The results show that the method is effective and the detailed analysis shows that it is comparable to the best method in the world.
【学位授予单位】：中国科学院研究生院（空间科学与应用研究中心）
【学位级别】：博士
【学位授予年份】：2011
【分类号】：P182.62

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