| 其他摘要 | Solar coronal mass ejections (CMEs) are the largest known solar eruptive activity in spatial scale and also in energetics and geoeffectiveness. In such a process, a great deal of magnetized plasma and energy can be ejected into the outermost corona and interplanetary space within a short time, which can cause the strong interplanetary disturbances and effect satellite operation, aviation power, human space exploration, communication, navigation and so on. So CMEs are well related to human's lives and production activities. Nonequilibria of the large-scale magnetic fields can cause CMEs. CMEs are associated with many dynamical phenomena, e.g., Moreton waves, EIT waves, dimming and type II radio bursts. These phenomena can help us to study the properties of CMEs. Since some dynamical phenomena can help researchers investigate CMEs, these phenomena associated with CMEs attract our interests. In this thesis, MHD processes of CMEs are numerically simulated by using ZEUS code. We adopt MHD numerical experiment to study qualitatively some dynamical phenomena associated with the lift-off of flux rope, such as the Moreton waves, the EIT waves and the dimming in two different backgrounds which have the different plasma density distribution. We use the velocity divergence and vorticity to further discuss and investigate the Moreton waves and the EIT waves. We found that as the flux rope rises rapidly, a fast shock is formed in front of it like a piston when its velocity exceeds the local magnetoacoustic speed, and the slow shock is also formed, which draws near the top of the flux rope, at the same time, the velocity vortices are developed at the backside of the flux rope. The progation of these two shocks arrive the different height. The fast-mode shock arrives the solar surface, while the slow-mode shock and velocity vortices arrive some height above the surface. We also investigate the velocity of these two shocks and the local Alfvenic wave. Analyses show that the joint impact of the slow-mode shock and the vortices is quite likely to account for the EIT waves, when the fast-mode shock sweeps the chromosphere, it produces the Moreton waves. The piston-driven shock is the type II radio bursts. From our results, we also found the dimming with the lift-off flux rope. Our simulation shows the dimming is more likely caused by a loss in density. In addition, we investigated the evolutionary features of the magnetic configuration that includes a current-carrying flux rope, which used to model the filament in two different backgrounds. We discussed our results and the reported theoretical results. At last, we investigate the algorithm in another code-CANS(Coordinated Astronomical Numerical Software). We modify this algorithm, and provide the new preconditioned methods. From the theoretical proof and numerical experiments, we can conclude that our new preconditioners are more effective to accelerate convergence than the previous methods. |
修改评论