横向非均匀太阳大气磁结构中的集体模式

发布时间：2018-06-03 14:24

本文选题：冕震学 + 腊肠模　；参考：《山东大学》2016年博士论文

【摘要】：SOHO, TRACE, Hinode和SDO等卫星升空后,在高度结构化的太阳大气中发现了大量的低频波动和震荡。波动参数的测量,结合日冕磁结构中集体磁流体波动模式的理论,即可推测难以直接测量的关键日冕物理参数,这就是“冕震学”的研究内容。冕震学推测对象中,Alfven速和大气结构的横向密度梯度备受关注。然而,作为冕震学的理论出发点,日冕磁结构常被描述成静态的、密度由内到外是跃变的。本文利用解析和数值计算,较为系统地讨论了磁结构内外流动剪切、密度横向不均匀性对若干主流冕震学诊断手段的影响。所取得成果具有如下主要创新点：(1)首次系统讨论了流动剪切对磁环中驻波的效应,发现该剪切可显著影响环内快扭曲模基模谐模周期比,也可极大限制快腊肠驻波的可观测性；(2)首次给出了具有任意横向密度剖面的磁片结构中快波的色散关系并对其做了系统讨论,发现第一支扭曲波受密度分布细节影响不大,为以往的冕震学实践提供了理论支撑；但腊肠模及高支扭曲模的特性敏感地依赖于密度分布细节；(3)首次探讨了具有任意横向密度剖面的磁环中脉冲激发的腊肠行波,其结果表明,某些活动区磁环中腊肠行波信号不存在准周期相,这与经典结论有定性的区别。具体描述如下。观测表明,不少震荡的太阳大气磁环中存在多周期信号。在冕震学框架内,磁环中驻波基模周期(P1)与第一谐模周期(P2)之比在推断磁环介质的密度及磁场结构化信息方面起着重要作用。基于光谱测量的直接手段与基于冕震学思想的间接手段都表明磁环内可能存在可观的场向流。但迄今还少有研究来系统讨论磁环内外流动剪切对周期比这一冕震学手段的影响。本文第二章数值求解了带有流动的磁环中波模的色散关系,设计了一种简单的图形方法来构造驻波,从而首次系统考察了周期比P1/2P2对磁环横纵比(即半径一环长比)、环内流速以及环内外密度比的依赖。对于冕环,我们发现流动效应对快扭曲模和腊肠模的影响都很大：对快扭曲模,流动会使P1/2P2比静态时显著减小；对快腊肠模,流动对P1/2P2的影响有限,但会极大缩小支持束缚腊肠驻波的冕环的参数范围。对于光球磁环,流动对P1/2P2影响较弱,但考虑流动效应会为光球磁结构中腊肠模多周期现象的观测提供额外的理解方式。相对于磁环几何,磁片几何在解释若干太阳大气磁结构中集体波模(如白光观测所发现的冕流波)的观测方面更为适用。已有研究多假定磁片内外密度呈阶跃式变化。显然密度的横向连续变化更为现实,但其效应还少有研究。本文第三章在冷磁流体力学框架下,首次解析给出了具有任意横向密度剖面的日冕磁片中集体快波所满足的色散关系,并进而系统讨论了连续横向密度分布对日冕磁片中驻立扭曲模和腊肠模色散特性的影响。此外还通过数值求解相应的时变快波方程,说明了我们所关注的解析色散关系的解有其明确的物理意义。我们发现,至少对几种常用的横向密度剖面,对任意轴向波数,第一支扭曲模总是被束缚在磁片内。当轴向波数的取值在观测范围内时,与阶跃情形相比,引入密度剖面的连续分布所带来的该支扭曲模周期的变化不超过13%。但轴向波数较小时,腊肠模和其他支扭曲模是泄漏的,且其周期和衰减时间严重依赖于横向密度分布的描述。只有在耀斑环这类高密度比的磁结构中,这些模式的衰减才足够弱,以至于可被观测到。总体上看,对第一支扭曲模来说,阶跃剖面的色散关系在计入横向密度连续变化时仍大致适用；但对腊肠模和其他支扭曲模来说,其研究需要考虑横向密度分布的细节。近期紫外、可见光及射电观测表明,冕环中常出现准周期行波。从直观上讲,行波的这类准周期性可能来自激发源的准周期行为。但事实上,由于磁环中集体模式的色散,脉冲源也可导致行波的准周期性,此时集体模式轴向群速度(vgr)对角频率(ω)的依赖决定了行波的时变特征。由于其强色散性,束缚腊肠模在这一机制中备受关注。已有研究往往假定磁环内外密度呈阶跃式变化,此时随着ω的增加,束缚腊肠模的强先迅速下降继而缓慢增加,而这一非单调性是行波信号中存在准周期相的原因。基于我们以往所得具有任意密度剖面的冕环中腊肠波的色散关系,本文第四章讨论了横向连续密度剖面对脉冲激发的腊肠行波的影响。对于抛物剖面,无论环内外密度比以及密度横向变化尺度如何,群速度vgr对ω的依赖与阶跃剖面的经典结果都定性类似。换言之,如果磁环密度剖面可用抛物剖面刻画,那么脉冲激发的快腊肠行波信号总是包含准周期相。对线性剖面,群速度vgr随ω的变化对环内外密度比以及密度横向变化尺度有着复杂的依赖关系。对于较小的横向密度尺度,无论密度比如何,vgr-ω曲线的总体行为总与阶跃情形类似。但对于较大的横向密度尺度(换句话说,较为弥散的冕环),当密度比较小时,vgr-ω曲线呈单调变化,此时脉冲激发的快腊肠行波信号中不再存在准周期相。而当密度比较大时,vgr-ω曲线呈现多个极值。对同时存在一个极小和极大值的情形,我们的细致讨论表明,此时准周期相的持续时间、准周期相中信号的时变与小波谱特征都与阶跃情形不同。总体上说,对冕环中脉冲激发的快腊肠行波信号而言,冕环横向密度剖面的描述及其细节有着重要的影响。反过来说,这意味着快腊肠行波信号的细致测量可用来推测冕环横向密度剖面的细节。
[Abstract]:After the SOHO, TRACE, Hinode and SDO satellites are lifted, a large number of low frequency fluctuations and oscillations have been found in the highly structured solar atmosphere. Measurement of the fluctuation parameters and the theory of the wave mode of the collective magnetic fluid in the coronal magnetic structure can be used to speculate the key coronal physical parameters which are difficult to be measured directly. This is the study of "coronal earthquake". In the conjecture of coronal seismology, the Alfven velocity and the transverse density gradient of the atmospheric structure are concerned. However, as the starting point of the coronal seismology, the coronal magnetic structure is often described as static, and the density is leaped from inside to outside. In this paper, the internal and external shear and transverse density of the magnetic structure are systematically discussed by analytical and numerical calculations. The effect of inhomogeneity on the diagnostic methods of several mainstream coronal seismology. The results obtained are as follows: (1) the effect of the flow shear on the standing wave in the magnetic ring is discussed for the first time. It is found that the shear can significantly affect the periodic ratio of the basic mode harmonic mode in the ring, and can greatly limit the observability of the fast sausage standing wave; (2) the first time The dispersion relation of the fast wave in the magnetic sheet structure with arbitrary transverse density profile is given and a systematic discussion is given. It is found that the first twisted wave is less influenced by the details of density distribution, which provides theoretical support for the previous practice of coronal seismology; but the characteristics of the sausage mold and the high branch distortion die are sensitive to the details of the density distribution; (3) first. The results show that there is no quasi periodic phase in the traveling wave signal of the sausage in some active region magnetic rings, which is qualitatively different from the classical conclusion. The detailed description is as follows. The observations show that there are many periodic signals in many oscillating solar magnetic rings. The ratio of the base mode period (P1) and the first mode period (P2) in the magnetic ring plays an important role in inferring the density of the magnetic ring and the structural information of the magnetic field. The direct means based on the spectrometric measurement and the indirect means based on the theory of coronal seismology indicate that there may be a considerable field flow in the magnetic ring. But there are few studies to date. In the second chapter, a simple graphical method is designed to construct a standing wave. In this paper, a simple graphical method is designed to construct a standing wave, and for the first time, the cycle ratio of the P1/ 2P2 to the magnetic ring is investigated. For the coronal ring, we find that the flow effect has a great effect on the fast twisting die and the sausage mold: the flow will significantly reduce the P1/2P2 than the static mode for the fast warping die; the effect of the flow on the P1/2P2 is limited, but it will greatly reduce the parameters that support the coronal ring that supports the shackle of the sausage standing wave. The effect of flow on P1/2P2 is weak, but considering the flow effect will provide an additional understanding of the observation of the multiple periodic phenomena of the Dachshund model in the magnetic structure of the sphere. In the third chapter, the dispersion relation of the group fast wave in the coronal magnetic sheet with arbitrary transverse density profiles is given for the first time in the frame of cold magnetic fluid mechanics. Furthermore, the influence of the continuous transverse density distribution on the dispersion characteristics of the stationary distortion mode and the sausage model in coronal magnetic disc is discussed. In addition, the corresponding time-varying fast wave equation is solved by numerical calculation. It is shown that the solution of the analytical dispersion relation we have concerned has its clear physical meaning. We find at least several common transverse density profiles. For any axial wave number, the first twist die is always bound to the magnetic sheet. When the value of the axial wave number is in the range of observation, the variation of the period of the branch of the branch caused by the continuous distribution of the density profile is not more than 13%., but the axial wave number is less than the axial wave number, and the sausage die and the other branches of the branch are leaked. The period and time of attenuation depend heavily on the description of the distribution of transverse density. Only in the magnetic structure of the high density ratio of the flare ring, the attenuation of these modes is so weak that it can be observed. In general, the dispersion relation of the step section is still generally applicable to the first twist mode when the transverse density is taken into account. But for the dachshunds and other branches of the warp, it is necessary to consider the details of the distribution of transverse density. In the near future, UV, visible and radio observations show that quasi periodic traveling waves often occur in the coronal rings. The dispersion, the pulse source can also lead to the quasiperiodicity of the traveling wave. At this time, the dependence of the collective mode axial group velocity (vGr) on the angular frequency (omega) determines the time-varying characteristic of the traveling wave. Due to its strong dispersion, the bound sausage die has attracted much attention in this mechanism. In the fourth chapter, the effect of the transverse continuous density profile on the pulse excited sausage waves is discussed in the fourth chapter. On the parabolic profile, the dependence of the group velocity vGr on Omega is similar to the classical results of the step section, regardless of the density ratio and the lateral density. In other words, if the magnetic ring density profile can be depicted with a parabolic profile, the pulse excited fast sausage traveling wave signal always contains quasi periodic phase. The degree vGr has a complex dependence on the density ratio of the inner and outer density and the scale of the density. For the smaller transverse density scale, the overall behavior of the vgr- Omega curve is similar to the step situation regardless of the density ratio. But for the larger transverse density scale (in other words, the more dispersed coronal rings), when the density is smaller When the vgr- Omega curve is monotonically changing, the quasi periodic phase is no longer in the fast salami traveling wave excited by the pulse. And when the density is large, the vgr- Omega curve presents multiple extremes. For the case of a minimum and maximum value, our detailed discussion shows that the duration of the quasi periodic phase and the time variation of the signal in the quasi periodic phase are shown at this time. The characteristics of the small wave spectrum are different from the step conditions. In general, the description and details of the transverse density profile of the coronal ring have an important influence on the fast sausage traveling wave signals excited by the coronal rings. In turn, this means that the careful measurement of the fast sausage traveling wave signal can be used to speculate on the details of the transverse density profile of the coronal ring.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P182

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