日珥形成的數(shù)值模擬研究
發(fā)布時間：2018-07-14 09:23
【摘要】：日珥是太陽大氣中美麗而復雜的等離子體活動現(xiàn)象,它們由低溫(～8000K)、稠密(1010—1011cm-3)的等離子體組成,動態(tài)地懸浮在光球磁場中性線上方高溫稀薄的日冕中。日珥由許多向下伸出的足連接到光球。在日面上,日珥呈現(xiàn)為暗的條狀結(jié)構(gòu),因此又被稱為暗條。日珥的形成、維持和拋射等現(xiàn)象中的物理過程十分復雜,其中包含有輻射、熱傳導、加熱、磁場重聯(lián)、太陽重力等物理因素的非線性相互作用。對美麗而復雜的日珥現(xiàn)象進行解析的理論研究十分困難。因此,通常需要借助數(shù)值模擬才能進行定量的研究。本論文擬通過數(shù)值模擬對日珥的形成進行系統(tǒng)的研究。 前人的研究發(fā)現(xiàn)對磁環(huán)足點的加熱能夠引起色球蒸發(fā)。高溫等離子體充滿冕環(huán)后在一定條件下觸發(fā)輻射不穩(wěn)定性,進而導致物質(zhì)凝聚成日珥。在此基礎(chǔ)上,我們首先利用包含自適應(yīng)網(wǎng)格的輻射流體力學數(shù)值模擬,研究了在持續(xù)穩(wěn)定或有限時間段的色球局部加熱下,在一個固定位形的磁環(huán)中暗條形成的過程。與前人的研究不同,我們采用了具有淺磁凹陷結(jié)構(gòu)的低平磁環(huán)位形來模仿活動區(qū)附近暗條的磁場結(jié)構(gòu),還考慮了更精確的輻射損失。我們首次證明了線性熱不穩(wěn)定性理論可以解釋暗條形成時物質(zhì)凝聚的發(fā)生。模擬結(jié)果顯示在局部加熱開始2個多小時后,日冕物質(zhì)冷凝發(fā)生形成暗條物質(zhì)。取不同的局部加熱強度和衰減標高,暗條長度生長的速率范圍為800—4000km hr-1。我們還發(fā)現(xiàn)了決定暗條物質(zhì)最初形成時是一段還是兩段的條件。在不對稱局部加熱下,當兩段暗條物質(zhì)形成后,它們匯聚、合并成一段,然后沿磁環(huán)運動掉落到磁環(huán)足點。在持續(xù)穩(wěn)定的局部加熱下,這一動態(tài)過程循環(huán)地發(fā)生,周期為幾個小時。我們除了驗證前人的發(fā)現(xiàn)之外,還發(fā)現(xiàn)持續(xù)的局部加熱不是維持日冕物質(zhì)冷凝的必要條件。暗條物質(zhì)一旦形成,即使沒有局部加熱也能夠由于虹吸作用緩慢生長。此外,我們發(fā)現(xiàn)暗條在光球p模波的擾動下能夠穩(wěn)定存在。 在一維模型的基礎(chǔ)上,我們發(fā)展了日珥形成的2.5維蒸發(fā)—凝聚模型。在包含色球、過渡區(qū)和日冕的剪切磁拱中,我們利用2.5維輻射磁流體力學模擬,得到了正常極性寧靜日珥在日冕中的形成過程。集中于色球的加熱引起色球物質(zhì)蒸發(fā),日冕物質(zhì)密度升高、溫度先上升后下降,接著熱不穩(wěn)定發(fā)生,導致日冕物質(zhì)冷凝,最終在磁拱頂部形成了日珥。與前人的結(jié)果不同,我們的模擬展現(xiàn)了完整的日珥形成過程,其中包括熱平衡的破壞、日冕物質(zhì)冷凝、日珥在寬度和高度方向的生長、在日珥重力的作用下磁拱逐漸被壓彎形成磁凹陷。我們得到的日珥形如簾狀,懸浮在磁中性線上方,其中磁場方向與日珥長軸方向成一定的夾角。持續(xù)的色球加熱把色球物質(zhì)帶入日冕,然后冷凝進入日珥,使得日珥穩(wěn)定生長。我們首次證實了日珥形成的蒸發(fā)—凝聚模型在低氣壓磁壓比的日冕中可以得到受力平衡的日珥,并且這一結(jié)果可以和解析的Kippenhahn-Schluter靜態(tài)日珥模型相比較。 在論文的最后,我們對日珥形成的數(shù)值模擬與觀測研究進行了展望。
[Abstract]:Prominence is a beautiful and complex plasma activity in the solar atmosphere. They are composed of low temperature (~ 8000K), dense (1010 - 1011cm-3) plasma, which are dynamically suspended in the thin corona above the neutral line of the photospheric magnetic field. The prominence is connected to the ball of light from a number of downward legs. The prominence of the prominence is a dark strip on the surface. It is also known as a dark strip. The physical processes in the formation, maintenance and ejection of prominence are very complicated, including the nonlinear interaction of physical factors such as radiation, heat conduction, heating, reconnection of the magnetic field, and the solar gravity. It is very difficult to analyze the beautiful and complex prominence phenomena. Only by numerical simulation can we conduct quantitative research. This paper intends to systematically study the prominence formation through numerical simulation.
Previous studies have found that the heating of the foot of a magnetic loop can cause chromosphere evaporation. The high temperature plasma is filled with a coronal ring and triggers the radiation instability under a certain condition, which leads to the condensation of the material into a prominence. Different from previous studies, we adopt a low level magnetic ring position with a shallow magnetic depression to mimic the magnetic structure of a dark strip near the active area and consider more accurate radiation loss. We have first proved linear thermal instability. The theory of sex can explain the occurrence of material condensation at the formation of a dark strip. The simulation results show that after 2 hours of local heating, coronal mass condensation occurs to form a dark strip. Different local heating intensity and attenuation elevation are taken. The rate range of the growth of the length of the dark strip is 800 - 4000km hr-1.. We also found that the dark strip was initially determined. Under asymmetric local heating, when the two sections of dark strips are formed, they converge and merge into one section, and then fall along the magnetic ring to the foot of the ring. This dynamic process circularly occurs under steady and stable local heating. The cycle is a few hours. We have verified the discoveries of the predecessors. In addition, it is found that continuous local heating is not a necessary condition for maintaining coronal condensation. Once dark strips are formed, even without local heating, the growth of the siphon can be slowed down. In addition, we find that the dark strips can be stable under the perturbation of the P mode wave of the photosphere.
On the basis of one dimensional model, we developed a 2.5 dimensional evaporation condensation model of prominence. In the shear magnetic arches containing chromosphere, transition zone and corona, we use 2.5 dimensional radiation magnetohydrodynamic simulation to obtain the formation process of normal polar tranquil prominence in the corona. The coronal mass density rises, the temperature rises first and then decreases, then the thermal instability occurs, resulting in the condensation of the coronal matter and the formation of a solar prominence at the top of the magnetic arch. Unlike the previous results, our simulation shows a complete process of prominence, including the destruction of the heat balance, the condensation of the coronal matter, the birth of the prominence in width and height. Under the action of the prominence of the solar prominence, the magnetic arch is gradually formed to form a magnetic depression. The prominences we get are like a curtain like, suspended above the magnetic neutral line, in which the direction of the magnetic field is in a certain angle with the long axis of the prominence. The continuous chromosphere is heated to bring the chromosphere into the corona and then cold to enter the prominence, making the prominence growing steadily. For the first time, we have grown. It is confirmed that the evaporation and condensation model of prominence can obtain a force balance prominence in the corona of low pressure magnetic pressure ratio, and this result can be compared with the analytic Kippenhahn-Schluter static prominence model.
At the end of the paper, we prospected the numerical simulation and observational research of prominence formation.
【學位授予單位】：南京大學
【學位級別】：博士
【學位授予年份】：2012
【分類號】：P182
本文編號：2121202
[Abstract]:Prominence is a beautiful and complex plasma activity in the solar atmosphere. They are composed of low temperature (~ 8000K), dense (1010 - 1011cm-3) plasma, which are dynamically suspended in the thin corona above the neutral line of the photospheric magnetic field. The prominence is connected to the ball of light from a number of downward legs. The prominence of the prominence is a dark strip on the surface. It is also known as a dark strip. The physical processes in the formation, maintenance and ejection of prominence are very complicated, including the nonlinear interaction of physical factors such as radiation, heat conduction, heating, reconnection of the magnetic field, and the solar gravity. It is very difficult to analyze the beautiful and complex prominence phenomena. Only by numerical simulation can we conduct quantitative research. This paper intends to systematically study the prominence formation through numerical simulation.
Previous studies have found that the heating of the foot of a magnetic loop can cause chromosphere evaporation. The high temperature plasma is filled with a coronal ring and triggers the radiation instability under a certain condition, which leads to the condensation of the material into a prominence. Different from previous studies, we adopt a low level magnetic ring position with a shallow magnetic depression to mimic the magnetic structure of a dark strip near the active area and consider more accurate radiation loss. We have first proved linear thermal instability. The theory of sex can explain the occurrence of material condensation at the formation of a dark strip. The simulation results show that after 2 hours of local heating, coronal mass condensation occurs to form a dark strip. Different local heating intensity and attenuation elevation are taken. The rate range of the growth of the length of the dark strip is 800 - 4000km hr-1.. We also found that the dark strip was initially determined. Under asymmetric local heating, when the two sections of dark strips are formed, they converge and merge into one section, and then fall along the magnetic ring to the foot of the ring. This dynamic process circularly occurs under steady and stable local heating. The cycle is a few hours. We have verified the discoveries of the predecessors. In addition, it is found that continuous local heating is not a necessary condition for maintaining coronal condensation. Once dark strips are formed, even without local heating, the growth of the siphon can be slowed down. In addition, we find that the dark strips can be stable under the perturbation of the P mode wave of the photosphere.
On the basis of one dimensional model, we developed a 2.5 dimensional evaporation condensation model of prominence. In the shear magnetic arches containing chromosphere, transition zone and corona, we use 2.5 dimensional radiation magnetohydrodynamic simulation to obtain the formation process of normal polar tranquil prominence in the corona. The coronal mass density rises, the temperature rises first and then decreases, then the thermal instability occurs, resulting in the condensation of the coronal matter and the formation of a solar prominence at the top of the magnetic arch. Unlike the previous results, our simulation shows a complete process of prominence, including the destruction of the heat balance, the condensation of the coronal matter, the birth of the prominence in width and height. Under the action of the prominence of the solar prominence, the magnetic arch is gradually formed to form a magnetic depression. The prominences we get are like a curtain like, suspended above the magnetic neutral line, in which the direction of the magnetic field is in a certain angle with the long axis of the prominence. The continuous chromosphere is heated to bring the chromosphere into the corona and then cold to enter the prominence, making the prominence growing steadily. For the first time, we have grown. It is confirmed that the evaporation and condensation model of prominence can obtain a force balance prominence in the corona of low pressure magnetic pressure ratio, and this result can be compared with the analytic Kippenhahn-Schluter static prominence model.
At the end of the paper, we prospected the numerical simulation and observational research of prominence formation.
【學位授予單位】：南京大學
【學位級別】：博士
【學位授予年份】：2012
【分類號】：P182
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，本文編號：2121202
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