日冕亮点和日珥纵向振荡的高分辨率观测及其模拟研究

发布时间：2018-06-08 15:14

本文选题：日冕亮点 + 日珥振荡　；参考：《南京大学》2012年博士论文

【摘要】：日冕亮点是日冕中一种长寿命的小尺度增亮现象。人们普遍认为日冕亮点的加热机制是磁重联,但是关于它们的磁拓扑结构和重联的方式还知之甚少。我们利用高分辨率的Hinode/XRT和STEREO/EUVI望远镜的多波段观测资料仔细分析了2007年3月16日在日面中心附近的一大一小两个亮点。其光变曲线的特征都是长时间的增亮叠加若干间隔约1小时的准周期闪耀。我们据此提出亮点的光变曲线由两部分组成：缓慢的增亮和剧烈的闪耀。较大的亮点在闪耀期间总是伴随喷流的发生。基于光球视向磁图的势场外推显示两个亮点的上方均出现磁零点,都有穹顶状的扇面以及穿过顶点处磁零点的脊线。根据亮点的三维磁拓扑结构,我们认为亮点的闪耀和喷流源于零点处的剧烈磁重联,而长时间的缓慢增亮源于扇面的交换式(分量)重联。尽管高温极紫外波段观测到的日冕亮点与软X波段观测到的非常相似,但是低温极紫外波段的观测显示亮点在日冕低层是由尖角状的磁环和周围几个分散的亮核组成,它们分别源于零点附近和扇面的磁重联。暗条的纵向振荡之前已经在Ha波段被观测到。我们利用高分辨率的多波段观测资料仔细研究了2007年2月8日太阳西边缘的活动区日珥振荡事件。Hinode/SOT的高分辨率观测显示在低分辨率的极紫外波段看到的向外凸的日珥在高分辨率的Ca Ⅱ H图像上其实是由许多向外凹的纤维组成,这也暗示了日珥中磁凹陷的存在。一团日珥物质注入到磁凹陷结构后开始沿磁力线来回振荡,并持续了至少三个半小时,周期约52分钟。振幅随时间指数衰减,衰减时标约133分钟。此外,我们也探讨了日珥纵向振荡作为后来日珥部分抛射以及日冕物质抛射(CME)前兆特征的可能性。为了进一步探讨日珥作为整体纵向振荡的触发机制、衰减机制和回复力,我们利用公开的MPI-AMRVAC程序对日珥纵向振荡进行了一维辐射流体力学数值模拟。模拟的第一步是冷而密的日珥物质由于色球蒸发和热不稳定性在预先设定的磁凹陷中形成并生长。色球加热停止后,日珥自发松弛到热力学平衡态。静止的日珥在脉冲式的扰动作用下沿磁凹陷周期性振荡。我们首先利用Hinode/SOT高分辨率观测到的日珥磁凹陷位形作为初始条件进行模拟,模拟的振荡周期与观测值非常接近,意味着日珥重力沿磁环的分量是纵向振荡的回复力。模拟中振幅的衰减时标比观测值长约1.5倍。我们发现辐射损失是导致振荡衰减的主要因素,但不足以使振荡迅速衰减。今后的模拟或许应该加入波的泄漏等机制。之后,我们通过改变各种物理参数和磁环位形进行了大量模拟。结果表明磁环腿部脉冲加热和日珥的初始速度扰动都可以推动日珥整体同相位振荡。振幅随扰动的增加而增加,随凹陷深度的增加而减小。当扰动非常强的时候,部分日珥物质会沿磁环腿部落到色球,导致质量和动能的损失。日珥振荡周期与扰动无关,而是正比于2w／(?),其中2w和D分别代表凹陷的总长度和深度,这与单摆有点类似。沿磁环的重力分量是主要的回复力。在非绝热情况下,日珥振荡随时间衰减,衰减时标和衰减率(衰减时标与周期的比值)都随周期的增加而减小。当扰动非常强的时候,物质掉落也会加快振荡的衰减。
[Abstract]:The coronal highlight is a small scale brightening phenomenon of a long life in the corona. It is widely believed that the heating mechanism of the coronal highlights is the magnetic reunion, but little is known about their magnetic topology and reconnection. We carefully analyzed the multi band observations of the high resolution Hinode/XRT and STEREO/EUVI telescopes in 2007. 16 of the two bright spots near the center of the diurnal center on July 16. The characteristics of the light variation curves are the long time brightening and the quasi periodic blazed of several intervals of some 1 hours. Accordingly, we propose that the light curve of the bright spot consists of two parts: slow brightening and intense glitter. The larger bright spots always accompany the jet during the blazed. An extrapolation of the potential field based on the photomagnetic view shows that there are magnetic zeros above the two bright spots, all with a dome like sector and a ridge line passing through the magnetic zeros at the vertex. Although the coronal bright spot observed in the high temperature ultra violet band is very similar to that observed in the soft X band, the observation of the low temperature ultra violet band shows that the bright spot is made up of a sharp corner magnetic ring and several scattered bright nuclei around the coronal lower layer, which are derived from the magnetic reconnection near the zero point and the fan surface.
The longitudinal oscillations of the dark strip have been observed before the Ha band. Using high resolution multiband observations, we carefully studied the high resolution observation of the active area prominence of the west edge of the sun in February 8, 2007, which shows that the prominence of the prominence of the prominence of the solar prominence at the low resolution of the ultra violet band is at a high resolution of Ca. The second H image is actually made up of many concave fibers, which also implies the existence of a magnetic depression in the prominence. A mass of prominence substances oscillates back and forth along the magnetic line after a magnetic depression, and continues for at least 3.5 hours for about 52 minutes. The amplitude attenuates with time exponentially and is marked for about 133 minutes. In addition, we also The possibility of vertical oscillation of prominence as a precursor of partial prominence and coronal mass ejection (CME) is discussed.
In order to further explore the triggering mechanism of the prominence as a whole longitudinal oscillation, the attenuation mechanism and the restoring force, we use the open MPI-AMRVAC program to simulate the one dimensional radiic hydrodynamics of the prominence longitudinal oscillation. The first step is the cold and dense prominence of the matter due to the color sphere evaporation and the thermal instability in the pre set magnetic field. After the stopping of the chromosphere, the prominence of the solar prominence spontaneously relaxes to the thermodynamic equilibrium state. The stationary prominence is periodically oscillating along the magnetic depression under the impulse of the pulse type. First, we use the magnetic depression of the prominence observed by Hinode/SOT as the initial condition to simulate the oscillation period and the observed value. It is very close, which means that the component of the gravitational force along the magnetic ring is the restoring force of the longitudinal oscillation. The attenuation of the amplitude in the simulation is about 1.5 times longer than the observed value. We find that the radiation loss is the main factor that causes the oscillation attenuation, but it is not enough to make the oscillation decay rapidly. A large number of simulations have been made by changing various physical parameters and magnetic ring positions. The results show that both the pulse heating of the leg and the initial velocity disturbance of the prominence can promote the overall same phase oscillation of the prominence. The amplitude increases with the increase of the disturbance and decreases with the increase of the depth of the depression. When the disturbance is very strong, the part of the matter of the prominence will be along the magnetic field. The ring leg tribes, to the chromosphere, cause the loss of mass and kinetic energy. The oscillation period of the prominence is independent of the disturbance, but is proportional to the 2W / (?), in which the 2W and D represent the total length and depth of the depression, which are similar to the single pendulum. The gravity component along the magnetic ring is the main recovery force. In the non adiabatic case, the prominence oscillation attenuates with time, attenuates the time mark and The attenuation rate (the ratio of decay time scale to cycle) decreases with the increase of cycle. When the disturbance is very strong, the falling of matter also accelerates the attenuation of oscillation.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2012
【分类号】：P182

【共引文献】