日冕磁片所支持的驻立扭曲模与腊肠模：流动的效应

发布时间：2018-03-20 16:05

本文选题：磁流体力学(MHD)-太阳　切入点：日冕-太阳　出处：《山东大学》2013年硕士论文　论文类型：学位论文

【摘要】：传统上,光谱观测是太阳大气物理参数诊断的主要方法。但是,“磁震学”这一间接手段随着大量的低频波和震荡观测而受到越来越多的重视。另一方面,已有观测证实振荡结构中存在多周期现象。在磁震学应用中,越来越多的研究者考虑利用基模周期与高次谐模周期之比来推测大气的结构化特征。进一步地,观测证实太阳大气震荡结构中普遍存在纵向流动,且Alfven速度量级的流动也并不罕见。这类流动对于由磁震学推测得到的冕环参数有着不可忽视的影响,但其对多周期特性的影响至今仍无系统研究,而这正是本文的研究对象。我们采用磁片模型。一方面,其结果可作为磁环模型的有力的理论参考,另一方面,这一选择使我们可以与目前仅有的静态磁片的解析结果(MacnaramaRoberts2011)直接比较,从而无歧义地推断流动对于磁片所支持驻波的多周期行为的影响。由一般磁流体(MHD)方程组出发,我们对于流动磁片所支持的行波色散特性进行了系统考察。此后,基于色散图形,我们构建了一种用于驻波周期比计算的简单图形方法,从而系统探讨了片内流动对于驻立kink模和sausage模之周期比的影响。考虑有限βMHD环境,我们发现背景流动的存在增强了快波的色散,但是其对于kink模和sausage模的影响并不相同。对于kink模,相较于静态情形,流动所引起的P1/2P2减小幅度可达23%。且当存在一定流动时,(P1/2P2)min会显著低于静态情形的解析下限值(0.707)。特别地,即使对于细磁片情形,流动所引起的P1/2P2变化依旧不可忽略。对于sausage模,相较于静态情形,流动引起的P1/2P2减小不如kink模那么明显,其幅度为5%左右。但是它使得支持驻波出现的磁片截止横纵比(d/L)cutoff增大至静态情形时的几倍。这极大地限制了驻立sausage模的可观测性。我们的方法并不局限于日冕环境,而适用于任意β的情形。但考虑低β日冕环境中,有限温度效应对于快模色散特性影响较小这一特点,我们采用零βMHD来对磁片模型进行描述。此时,驻波色散特性只取决于两个因素：磁片内外密度比ρ0/ρe和Alfven马赫数MA(以片内Alfven速度来衡量的片内流速)。我们系统探讨了流动横向结构化对于驻立kink模和sausage模的基模与高次谐模周期之化(包括1次、2次和3次谐模)的影响。发现对于kink模,当ρ0/ρe较大时,背景流动使得三类周期比(P1/2P2、P1/3P3和P1/4P4)的减小幅度甚至能达到30%以上。且流动增大到一定后,三类周期比最小值都会显著小于静态情形下的解析最小值(即0.707、0.577和0.5)。对于sausage模,流动所引起的周期比的整体减小幅度并不是那么明显。但是,它的存在使得(d/L)cutoff相较于静态情形的值可能大上一个量级。由此我们得到结论：当日冕磁片中存在明显流动时,其所引起的周期比影响必须要被计入到多周期现象的磁震学应用中。
[Abstract]:Traditionally, spectral observation is the main method to diagnose the physical parameters of the solar atmosphere. However, the indirect method of "magnetoseismology" has been paid more and more attention with a large number of low-frequency waves and oscillations. On the other hand, It has been observed that there is a multi-period phenomenon in oscillatory structures. In the application of magnetoseismology, more and more researchers are considering using the ratio of the fundamental mode period to the high-order harmonic mode period to predict the structural characteristics of the atmosphere. The observations show that longitudinal flow exists generally in the solar atmospheric oscillation structure, and that the flow of the order of Alfven velocity is not uncommon. This kind of flow has an important influence on the coronal ring parameters inferred from the magnetoseismology. However, its influence on multi-period characteristics is still not systematically studied, and this is the object of this paper. We use the magnetic disk model. On the one hand, the results can be used as a powerful theoretical reference for the magnetic ring model. On the other hand, this choice allows us to compare directly with the only analytical results of the static magnetic disk, Macnarama Roberts2011. Therefore, we infer inambiguously the effect of flow on the multi-period behavior of standing waves supported by magnetic plates. Starting from the general MHD equations, we systematically investigate the dispersion characteristics of traveling waves supported by mobile magnetic disks. Based on the dispersive figure, we construct a simple graphic method for calculating standing wave period ratio, and systematically discuss the influence of in-cell flow on the period ratio of standing kink mode and sausage mode. Considering the finite 尾 MHD environment, we find that the existence of background flow enhances the dispersion of fast waves, but its effects on kink mode and sausage mode are different. For kink mode, compared with static case, The decrease of P1 / 2P2 caused by flow can be as large as 23. And when there is a certain flow, the P1 / 2P2pmin is significantly lower than the analytical lower limit of 0.707m in the static case. In particular, even in the case of fine magnetic disk, the change of P1 / 2P2 caused by flow cannot be ignored. For the sausage mode, Compared with the static case, the P1 / 2P2 decrease caused by the flow is not as obvious as the kink mode. The amplitude is about 5%, but it increases the cut-off transverse to longitudinal ratio of d / L to several times that in the static case, which greatly limits the observability of the standing sausage mode. Our method is not limited to the coronal environment, but is suitable for arbitrary 尾. However, in the low 尾 coronal environment, the finite temperature effect has less effect on the fast mode dispersion. We use zero 尾 MHD to describe the wafer model. Standing wave dispersion depends only on two factors: density ratio 蟻 0 / 蟻 e and Alfven Mach number MA (intrachip velocity measured by intrachip Alfven velocity). We systematically discuss the fundamental modes of flow transverse structuring for standing kink mode and sausage mode. The effects of the cycles of higher order harmonic modules (including 1 order harmonic mode and 3 order harmonic mode) are obtained. It is found that for kink modules, When 蟻 _ 0 / 蟻 _ e is larger, the background flow causes the decrease of the three kinds of periods than that of P _ (1 / 2) P _ (2) P _ (2) P _ (1) P _ (3) P _ (3) and P _ (1 / 4) P _ (4) can be more than 30%, and the flow increases to a certain extent. The minimum values of the three types of periodic ratios will be significantly smaller than the analytical minimum values in the static case (i.e. 0.707 / 0. 577 and 0. 5). For the sausage mode, the overall decrease of the period ratio caused by the flow is not so obvious. However, Because of its existence, the value of d / L cutoff may be one order of magnitude larger than that of the static case, and we conclude that when there is an obvious flow in the coronal disk, The period ratio effect caused by it must be taken into account in the magnetoseismological application of multi-period phenomena.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：P182

【共引文献】