【摘要】：磁層頂通量傳輸事件(Flux Transfer Event,FTE)被認(rèn)為是與磁場(chǎng)重聯(lián)相關(guān)的現(xiàn)象,其標(biāo)志為衛(wèi)星測(cè)量磁場(chǎng)在磁層頂法向分量的雙極變化。迄今為止,關(guān)于FTE的本質(zhì)、形成機(jī)制和產(chǎn)生位置這些基本問題還存在著一些爭(zhēng)論。確定FTE的軸向不僅對(duì)于研究FTE的幾何結(jié)構(gòu)以及理解其中等離子體動(dòng)力學(xué)是必要的,也可以幫助我們區(qū)分FTE的不同形成機(jī)制和產(chǎn)生位置。本文以FTE軸向研究為主線,主要內(nèi)容及結(jié)論總結(jié)如下:(1)發(fā)展了一種新的多點(diǎn)分析方法去確定FTE的軸向。這種方法建立在結(jié)構(gòu)為左右對(duì)稱的純幾何假設(shè)上,對(duì)于嵌在磁層頂電流片中的FTE結(jié)構(gòu),不管其物理性質(zhì)如何,都基本上滿足這一對(duì)稱條件,所以新方法就有著較廣泛的應(yīng)用性。模型測(cè)試和實(shí)際應(yīng)用表明,新的方法在確定軸向時(shí)比傳統(tǒng)方法如Grad-Shafranov(GS)方法和磁場(chǎng)最小方差分析法等以及更近的基于圓柱對(duì)稱的方法更有效和可靠。(2)在確定了FTE軸向以及在合適的多衛(wèi)星位形下,設(shè)計(jì)了一種新方法去重構(gòu)FTE磁場(chǎng)的空間分布。該方法對(duì)THEMIS和Cluster各自觀測(cè)到的兩個(gè)FTE的應(yīng)用表明它能快速而有效地重構(gòu)出結(jié)構(gòu)的磁場(chǎng)空間分布,從而幫助我們推測(cè)結(jié)構(gòu)磁場(chǎng)位形、理解衛(wèi)星測(cè)量數(shù)據(jù)的時(shí)間變化以及獲得其它物理量相對(duì)于結(jié)構(gòu)磁場(chǎng)的空間分布特征。(3)利用新的FTE軸向確定方法進(jìn)行了首個(gè)關(guān)于FTE軸向的統(tǒng)計(jì)分析。其結(jié)果揭示出:盡管在昏側(cè)低緯觀測(cè)到的FTE大多有著接近南北方向的軸向,其來(lái)源仍然是日下點(diǎn)分量重聯(lián)線;與傳統(tǒng)認(rèn)識(shí)中日下點(diǎn)分量重聯(lián)線為一條方向幾乎不變的分隔線不同,實(shí)際的日下點(diǎn)分量重聯(lián)線在磁層頂有著相當(dāng)大的曲率。(4)首次發(fā)現(xiàn)多X線重聯(lián)形成FTE的磁場(chǎng)信號(hào)。這種磁場(chǎng)信號(hào)的表征為的多極變化(比如雙或者三-雙極變化)。GS重構(gòu)結(jié)果表明在有著如此磁信號(hào)的事件中包括多個(gè)子結(jié)構(gòu),這與多X線重聯(lián)形成多個(gè)通量管的圖景相符;但各子結(jié)構(gòu)在磁層頂上依序從大到小排列,這一特征是傳統(tǒng)的多X線重聯(lián)模型所未預(yù)測(cè)到的。為解釋這一現(xiàn)象,我們提出了一個(gè)新的模型去描述FTE的形成過程:重聯(lián)持續(xù)在磁層頂發(fā)生,在主X線附近磁場(chǎng)形成楔形位形;重聯(lián)率周期性地變化,在其增長(zhǎng)時(shí)楔形磁場(chǎng)線內(nèi)由撕裂模不穩(wěn)定性形成了連續(xù)的多個(gè)小尺寸的磁島結(jié)構(gòu);這些小的磁島結(jié)構(gòu)互相合并,由于楔形磁場(chǎng)的限制,形成按尺寸大小依序排列的多個(gè)FTE,最后在磁鞘流壓力和磁張力作用下離開重聯(lián)位置。(5)分析了在昏側(cè)低緯磁層頂內(nèi)遙測(cè)到的一系列“反常”日向運(yùn)動(dòng)的連續(xù)FTE。將事件的運(yùn)動(dòng)速度與FTE運(yùn)動(dòng)模型相比較可發(fā)現(xiàn),為對(duì)抗此時(shí)在昏側(cè)磁層頂附近較大的尾向磁鞘流速度,實(shí)際重聯(lián)磁場(chǎng)的磁張力要比模型給出的磁張力大很多,這說明在磁流體動(dòng)力學(xué)效應(yīng)可能起重要作用的時(shí)候,現(xiàn)有模型并不能準(zhǔn)確地描述磁鞘磁場(chǎng)和等離子體環(huán)境,因此需要修正。
[Abstract]:The magnetopause flux transmission event (Flux Transfer Event,FTE) is considered to be a phenomenon related to the reconnection of the magnetic field, which is marked by the bipolar variation of the normal component of the magnetic field measured by the satellite at the top of the magnetopause. So far, there are still some debates about the essence, formation mechanism and location of FTE. It is necessary to determine the axial direction of FTE not only to study the geometric structure of FTE and to understand the plasma dynamics, but also to help us distinguish the different formation mechanism and generation position of FTE. In this paper, the axial research of FTE is taken as the main line, and the main contents and conclusions are summarized as follows: (1) A new multi-point analysis method is developed to determine the axial direction of FTE. This method is based on the pure geometric assumption that the structure is left and right symmetry. For the FTE structure embedded in the magnetopause current sheet, regardless of its physical properties, it basically satisfies this symmetry condition, so the new method has a wide range of applications. The model test and practical application show that, The new method is more effective and reliable in determining the axial direction than the traditional methods such as Grad-Shafranov (GS) method and magnetic field minimum variance analysis method, as well as the closer method based on cylindrical symmetry. (2) the axial and coincidence of FTE are determined. Under the suitable multi-satellite configuration, A new method is designed to reconstruct the spatial distribution of FTE magnetic field. The application of this method to the two FTE observed by THEMIS and Cluster respectively shows that it can reconstruct the magnetic field spatial distribution of the structure quickly and effectively, thus helping us to speculate the magnetic field configuration of the structure. Understand the time variation of satellite measurement data and obtain the spatial distribution characteristics of other physical quantities relative to the structural magnetic field. (3) the first statistical analysis of FTE axis is carried out by using the new FTE axial determination method. The results show that although most of the FTE observed in the low latitudes of the fainting side have an axial direction close to the north and south, the source is still the subsolar component reconnection line. Different from the traditional understanding that the Japanese and lower point component reconnection line is a separation line with almost unchanged direction, the actual diurnal point component reconnection line has considerable curvature at the top of the magnetosphere. (4) for the first time, it is found that the magnetic field signal of FTE is formed by multi-X-ray reconnection. GS reconstruction results show that there are multiple substructures in events with such magnetic signals, which is consistent with the pattern of multiple flux tubes formed by reconnection of multiple X-rays. However, the substructures are arranged sequentially from large to small on the top of the magnetosphere, which is not predicted by the traditional multi-X-ray reconnection model. In order to explain this phenomenon, we propose a new model to describe the formation process of FTE: reconnection continues to occur at the top of the magnetosphere and forms a cuneiform configuration in the magnetic field near the main X-ray; The reconnection rate changes periodically, and a continuous number of small island structures are formed by tearing mode instability in the cuneiform magnetic field line as it grows. These small magnetic island structures merge with each other, and due to the limitation of the cuneiform magnetic field, they form a number of FTE, arranged in order by size. Finally, under the action of magnetic sheath flow pressure and magnetic tension, the reconnection position is left. (5) A series of continuous FTE. of "abnormal" diurnal motion measured in the low latitude magnetopause of the fainting side are analyzed. By comparing the velocity of the event with the FTE motion model, it can be found that the magnetic tension of the actual reconnected magnetic field is much larger than that given by the model in order to counter the larger wake magnetic sheath velocity near the dizzy side magnetopause at this time. This shows that when the magnetohydrodynamic effect may play an important role, the existing model can not accurately describe the magnetic field and plasma environment, so it needs to be modified.
【學(xué)位授予單位】：中國(guó)科學(xué)院國(guó)家空間科學(xué)中心
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：P353

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