本文選題：磁流體力學(xué)(MHD)-太陽(yáng)　切入點(diǎn)：日冕-太陽(yáng)　出處：《山東大學(xué)》2013年碩士論文　論文類型：學(xué)位論文

【摘要】：傳統(tǒng)上,光譜觀測(cè)是太陽(yáng)大氣物理參數(shù)診斷的主要方法。但是,“磁震學(xué)”這一間接手段隨著大量的低頻波和震蕩觀測(cè)而受到越來越多的重視。另一方面,已有觀測(cè)證實(shí)振蕩結(jié)構(gòu)中存在多周期現(xiàn)象。在磁震學(xué)應(yīng)用中,越來越多的研究者考慮利用基模周期與高次諧模周期之比來推測(cè)大氣的結(jié)構(gòu)化特征。進(jìn)一步地,觀測(cè)證實(shí)太陽(yáng)大氣震蕩結(jié)構(gòu)中普遍存在縱向流動(dòng),且Alfven速度量級(jí)的流動(dòng)也并不罕見。這類流動(dòng)對(duì)于由磁震學(xué)推測(cè)得到的冕環(huán)參數(shù)有著不可忽視的影響,但其對(duì)多周期特性的影響至今仍無系統(tǒng)研究,而這正是本文的研究對(duì)象。 我們采用磁片模型。一方面,其結(jié)果可作為磁環(huán)模型的有力的理論參考,另一方面,這一選擇使我們可以與目前僅有的靜態(tài)磁片的解析結(jié)果(MacnaramaRoberts2011)直接比較,從而無歧義地推斷流動(dòng)對(duì)于磁片所支持駐波的多周期行為的影響。由一般磁流體(MHD)方程組出發(fā),我們對(duì)于流動(dòng)磁片所支持的行波色散特性進(jìn)行了系統(tǒng)考察。此后,基于色散圖形,我們構(gòu)建了一種用于駐波周期比計(jì)算的簡(jiǎn)單圖形方法,從而系統(tǒng)探討了片內(nèi)流動(dòng)對(duì)于駐立kink模和sausage模之周期比的影響。 考慮有限βMHD環(huán)境,我們發(fā)現(xiàn)背景流動(dòng)的存在增強(qiáng)了快波的色散,但是其對(duì)于kink模和sausage模的影響并不相同。對(duì)于kink模,相較于靜態(tài)情形,流動(dòng)所引起的P1/2P2減小幅度可達(dá)23%。且當(dāng)存在一定流動(dòng)時(shí),(P1/2P2)min會(huì)顯著低于靜態(tài)情形的解析下限值(0.707)。特別地,即使對(duì)于細(xì)磁片情形,流動(dòng)所引起的P1/2P2變化依舊不可忽略。對(duì)于sausage模,相較于靜態(tài)情形,流動(dòng)引起的P1/2P2減小不如kink模那么明顯,其幅度為5%左右。但是它使得支持駐波出現(xiàn)的磁片截止橫縱比(d/L)cutoff增大至靜態(tài)情形時(shí)的幾倍。這極大地限制了駐立sausage模的可觀測(cè)性。 我們的方法并不局限于日冕環(huán)境,而適用于任意β的情形。但考慮低β日冕環(huán)境中,有限溫度效應(yīng)對(duì)于快模色散特性影響較小這一特點(diǎn),我們采用零βMHD來對(duì)磁片模型進(jìn)行描述。此時(shí),駐波色散特性只取決于兩個(gè)因素：磁片內(nèi)外密度比ρ0/ρe和Alfven馬赫數(shù)MA(以片內(nèi)Alfven速度來衡量的片內(nèi)流速)。我們系統(tǒng)探討了流動(dòng)橫向結(jié)構(gòu)化對(duì)于駐立kink模和sausage模的基模與高次諧模周期之化(包括1次、2次和3次諧模)的影響。發(fā)現(xiàn)對(duì)于kink模,當(dāng)ρ0/ρe較大時(shí),背景流動(dòng)使得三類周期比(P1/2P2、P1/3P3和P1/4P4)的減小幅度甚至能達(dá)到30%以上。且流動(dòng)增大到一定后,三類周期比最小值都會(huì)顯著小于靜態(tài)情形下的解析最小值(即0.707、0.577和0.5)。對(duì)于sausage模,流動(dòng)所引起的周期比的整體減小幅度并不是那么明顯。但是,它的存在使得(d/L)cutoff相較于靜態(tài)情形的值可能大上一個(gè)量級(jí)。由此我們得到結(jié)論：當(dāng)日冕磁片中存在明顯流動(dòng)時(shí),其所引起的周期比影響必須要被計(jì)入到多周期現(xiàn)象的磁震學(xué)應(yīng)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.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2013
【分類號(hào)】：P182

【共引文獻(xiàn)】

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