太阳活动最引人注目的表现之一是在太阳大气的极紫外(EUV)图像中观察到的大规模日冕亮锋(CBF)。到目前为止,CBF的能量学和运动学仍然知之甚少,这是由于以前的EUV成像仪的低图像节奏和灵敏度以及用于提取特征的有限方法。在本文中,CBFs的轨迹和形态的确定,以调查CBFs的样品的变化特性,包括它们的运动学和脉冲形状,色散和耗散。我们已经开发了一种半自动强度分析技术,从STEREO/EUVI中提取2.5-10分钟节奏图像中CBFs的形态和准确位置。该技术被应用到序列的171 A和195 A的图像从STEREO/EUVI为了测量四个单独的CBF事件的波特性。在以~240- 450 km ^{-1}的速度发射后,所研究的四个事件中的每一个都显示出显著的负加速度,范围从~ -290到-60 ms ^{-2}。CBF的空间和时间宽度分别从~50 μ m增加到~200 μ m和~100 s增加到~1500 s,表明它们在本质上是分散的。位置-角度平均脉冲积分强度随传播的变化在所研究的四个事件中没有显示出明显的趋势。这些结果与CBF是色散磁声波最一致。
英文摘要:
One of the most dramatic manifestations of solar activity are large-scale coronal bright fronts (CBFs) observed in extreme ultraviolet (EUV) images of the solar atmosphere. To date, the energetics and kinematics of CBFs remain poorly understood, due to the low image cadence and sensitivity of previous EUV imagers and the limited methods used to extract the features. In this paper, the trajectory and morphology of CBFs was determined in order to investigate the varying properties of a sample of CBFs, including their kinematics and pulse shape, dispersion, and dissipation. We have developed a semi-automatic intensity profiling technique to extract the morphology and accurate positions of CBFs in 2.5-10 min cadence images from STEREO/EUVI. The technique was applied to sequences of 171A and 195A images from STEREO/EUVI in order to measure the wave properties of four separate CBF events. Following launch at velocities of ~240-450kms^{-1} each of the four events studied showed significant negative acceleration ranging from ~ -290 to -60ms^{-2}. The CBF spatial and temporal widths were found to increase from ~50 Mm to ~200 Mm and ~100 s to ~1500 s respectively, suggesting that they are dispersive in nature. The variation in position-angle averaged pulse-integrated intensity with propagation shows no clear trend across the four events studied. These results are most consistent with CBFs being dispersive magnetoacoustic waves.
Large-scale propagating fronts are frequently observed during solar eruptions, yet it is open whether they are waves or not, partly because the propagation is modulated by coronal structures, whose magnetic field we still cannot measure. However, when a front impacts coronal structures, an opportunity arises for us to look into the magnetic properties of both interacting parties in the low-$β$ corona. Here we studied large-scale EUV fronts accompanying three coronal mass ejections (CMEs), each originating from a kinking rope-like structure in the NOAA active region (AR) 12371. These eruptions …
On Formation Of A Shock Wave In Front Of A Coronal Mass Ejection With Velocity Exceeding The Critical One
新的研究证实了[M]中的结论。Eselevich,and V. Eselevich,2008];根据该理论,在日冕物质抛射前,存在一个沿CME传播方向扩展的扰动区,其速度$u$相对于周围日冕等离子体低于临界$u_C$。扰动区的时间差亮度(等离子体密度)在CME前向更远的距离平滑地减小。在扰动区的前部,在高于$u_C$的u处形成激波,表现为亮度差径向分布的不连续性。
Coronal and Chromospheric Signatures of Large-Scale Disturbances Associated with a Major Solar Eruption
我们提出了日冕和色球观测大规模的干扰与2005年9月7日的一个主要的太阳爆发。在GOES/SXI中,记录了在南半球传播的弧形日冕增亮。SXI锋面的初始速度为730 km/s $^{-1}$,之后逐渐减速,其中心位于日冕物质抛射(CME)的中心位置角附近,但远离耀斑中心。在MLSO/PICS H $α$和MLSO/CHIP He I 10830射电望远镜上都观测到了色球扰动的特征,并可分为两部分。南部的特征出现在SXI锋扫过的区域,H $α$亮锋与SXI锋重合,而He I暗锋落后于SXI锋,但显示出相似的运动学。在南方信号路径的前方,观察到一个暗条的振荡。北半球的特征出现在赤道附近,H $α$和He I锋相互重合。它们首先向西传播,然后在赤道冕洞(CH)的边界向北偏转。基于这些观测事实,我们认为全球扰动与CME的升空有关,并表现出一种混合性质:SXI签名和相应的南部色球签名的主要非波CME侧翼性质,和冲击快模式日冕磁流体动力学(MHD)波性质的北部色球签名。
In order to have a comprehensive view of the propagation and evolution of coronal mass ejections (CMEs) from the Sun to deep interplanetary space beyond 1 au, we carry out a kinematic analysis of 7 CMEs in solar cycle 23. The events are required to have coordinated coronagraph observations, interplanetary type II radio bursts, and multi-point in-situ measurements at the Earth and Ulysses. A graduated cylindrical shell model, an analytical model without free parameters and a magnetohydrodynamic model are used to derive CME kinematics near the Sun, to quantify the CME/shock propagation in the Su…
We used our newly developed magnetohydrodynamic (MHD) code to perform 2.5D simulations of a fast-mode MHD wave interacting with coronal holes (CH) of varying Alfvén speed which result from assuming different CH densities. We find that this interaction leads to effects like reflection, transmission, stationary fronts at the CH boundary and the formation of a density depletion that moves in the opposite direction to the incoming wave. We compare these effects with regard to the different CH densities and present a comprehensive analysis of morphology and kinematics of the associated secondary wa…
Investigation of the Formation and Separation of An EUV Wave from the Expansion of A Coronal Mass Ejection
我们通过直接观测由日冕物质抛射(CME)的膨胀及其随后从CME前沿分离驱动的漫射波的形成来解决EUV波的性质。2011年6月7日,太阳动力学天文台上的大气成像组件很好地观测到了波和CME。在太阳爆发开始之后,CME的速度和伴随耀斑的X射线通量开始迅速增加,CME表现出强烈的横向膨胀。在这个脉冲膨胀阶段,CME气泡的膨胀速度从100 km s $^{-1}$增加到450 km s $^{-1}$仅需6分钟。一个重要的发现是,扩散波前开始从前面的膨胀气泡后不久,横向膨胀放缓分离。此外,II型爆发形成的时间附近的分离。在分离之后,两个不同的锋以不同的运动学性质传播。漫射波前穿过整个太阳盘面,而尖锐的波前上升,形成CME喷出物,漫射波前在其前面。这些观测结果表明,以前称为EUV波是一种复合现象,由CME膨胀驱动。当日冕物质抛射加速膨胀时,波前与日冕物质抛射的波前是同空间的,因此这两个波前是不可分辨的。随着加速阶段的结束,波远离CME前沿,它们之间的距离逐渐增加。
Large-scale Coronal Propagating Fronts in Solar Eruptions as Observed by the Atmospheric Imaging Assembly on Board the Solar Dynamics Observatory\,--\,An Ensemble Study
A Data-Driven Analytic Model for Proton Acceleration by Large-Scale Solar Coronal Shocks
我们最近研究了低太阳日冕中爆发性日冕驱动的大规模离边日冕亮锋(OCBF)的发展(Kozarev et al. 2015),使用太阳动力学天文台高级成像组件EUV望远镜的远程观测。在这项研究中,我们获得了高时间分辨率的估计OCBF参数调节的效率内的扩散冲击加速(DSA)的理论框架内的带电粒子加速。这些参数包括时间依赖的前的大小,速度和强度,以及上游冠状磁场相对于前的表面法线方向的方向。在这里,我们提出了一个分析粒子加速度模型,专门开发,将日冕冲击/压缩前面的属性,从远程观测。我们验证了模型的性能,通过网格的理想化的情况下运行使用典型的大规模日冕冲击的输入参数,并表明,结果接近预期的DSA稳态行为。然后,我们使用Kozarev等人(2015)中推导的OCBF时间相关参数将模型应用于2011年5月11日的事件。我们发现,压缩前可能产生高能粒子低至1.3太阳半径的日冕。比较模拟的和观测到的地球附近的注量,我们还发现,在这一事件中的大部分加速必须发生在1.5太阳半径以上。通过这项研究,我们已经迈出了第一步,使用直接观测的冲击和压缩在最里面的日冕,以预测SEP事件的发生和强度。
Coronal Shock Waves, EUV waves, and their Relation to CMEs. II. Modeling MHD Shock Wave Propagation Along the Solar Surface, Using Nonlinear Geometrical Acoustics
Large-scale Bright Fronts in the Solar Corona: A Review of "EIT waves"
"EIT波”是大规模的日冕亮锋(CBF),首次在使用\emph{Solar and Heliospheric Observatory (SOHO)}上的极紫外成像望远镜(EIT)获得的195幅日冕图像中观察到。CBF通常被称为"EIT波”,它通常表现为以100- 700 km/s $^{-1}$的速度伪径向传播穿过太阳盘的扩散波前,波前宽度为50-100 μ m。($c_s\leq$ 200 km s $^{-1}$)和当地阿尔文速度($v_A\leq$ 1000 km s $^{-1}$),它们最初被解释为快模磁声波($v_{f}=(c_s^2 + v_A^2)^{1/2}$)。现在已知它们的传播会被磁声波速度变化的区域所改变,例如活动区域和冕洞,但也有证据表明冕洞边界处存在静止的CBF。后者导致了这样的建议,它们可能是焦耳加热或磁重联等过程的表现,而不是与波有关的现象。虽然CBF的一般形态学和运动学特性及其与日冕物质抛射的关系现在已经得到了很好的描述,但关于它们的激发和传播还有许多问题。特别是,这些神秘的事件作为磁流体动力学波或由于磁拓扑结构的变化的理论解释仍然是很多争论的话题。
自1996年{ \em Solar and Heliospheric Observatory}({ \em SOHO})发射升空以来,极紫外成像望远镜(EIT)观测到了一种全球性的日冕波现象,最初以该望远镜的名字命名为“EIT波”。明亮的锋面紧接着是不断扩大的暗淡。结果表明,等离子体的增亮和减暗主要是由于等离子体密度的增加和耗尽。这样一个壮观的现象引发了长期的兴趣和争论。争论集中在两个主题上,一个是关于驱动源,另一个是关于这种波动现象的本质。这些争论很可能是因为在{ \em Solar Dynamics Observatory}({ \em SDO})发射之前可能存在两种没有很好解决的大尺度日冕波:一种是横跨在爆发的日冕物质抛射(CME)上的活塞驱动冲击波,另一种是明显的传播锋,它可能对应于CME锋环。这种两波范式早在13年前就提出了,现在正被越来越多的同行所认可。在本文中,我们将回顾如何在两波框架中解决各种争议,以及为两种类型的日冕波提供两个不同名称的重要性。
Although the solar wind flows primarily outward from the Sun to interplanetary space, there are times when small-scale plasma inflows are observed. Inward-propagating density fluctuations in polar coronal holes were detected by the COR2 coronagraph on board the STEREO-A spacecraft at heliocentric distances of 7 to 12 solar radii, and these fluctuations appear to undergo substantial deceleration as they move closer to the Sun. Models of linear magnetohydrodynamic waves have not been able to explain these deceleration patterns, so they have been interpreted more recently as jets from coronal sit…
We present a new method to extract the three-dimensional electron density profile and density compression ratio of shock fronts associated with Coronal Mass Ejections (CMEs) observed in white light coronagraph images. We demonstrate the method with two examples of fast halo CMEs ($\sim$ 2000 km s$^{-1}$) observed on 2011 March 7 and 2014 February 25. Our method uses the ellipsoid model to derive the three-dimensional (3D) geometry and kinematics of the fronts. The density profiles of the sheaths are modeled with double-Gaussian functions with four free parameters and the electrons are distribu…
Recurrent, arc-shaped intensity disturbances were detected by EUV channels in an active region. The fronts were observed to propagate along a coronal loop bundle rooted in a small area within a sunspot umbra. Previous works have linked these intensity disturbances to slow magnetoacoustic waves that propagate from the lower atmosphere to the corona along the magnetic field. The slow magnetoacoustic waves propagate at the local cusp speed. However, the measured propagation speeds from the intensity images are usually smaller as they are subject to projection effects due to the inclination of the…
We developed a new numerical code that is able to perform 2.5D simulations of a magnetohydrodynamic (MHD) wave propagation in the corona, and its interaction with a low density region, such as a coronal hole (CH). We show that the impact of the wave on the CH leads to different effects, such as reflection and transmission of the incoming wave, stationary features at the CH boundary, or formation of a density depletion. We present a comprehensive analysis of the morphology and kinematics of primary and secondary waves, that is, we describe in detail the temporal evolution of density, magnetic f…
Spectroscopic analysis of interaction between an EIT wave and a coronal upflow region
我们报告了2010年6月12日发生在活动区11081的EIT波事件的光谱分析,该事件与M2.0级耀斑有关。波以近似圆形的方式传播。波阵面的东南部经过磁偶极附近的上升流区。利用该区域的EIS光栅观测,我们研究了波阵面中等离子体动力学的性质,以及波与上升流区域之间的相互作用。我们发现Fe XII λ195.12和Fe XIII λ202.04线在波前处有微弱的蓝移。由波阵面的视线速度和投影效应推导出的沿太阳表面的局部速度远低于波的典型传播速度。一个更有趣的发现是,在上升流区的上升流和非热的速度突然减少后,过境的波前。这意味着当波通过时磁场方向的显著变化。由于上流区域中的线被重定向,因此沿视线的速度减小。我们认为,这种情况是更符合所提出的EIT波的场线拉伸模型。
Estimated relations at a shock driven by a coronal mass ejection
SOHO/LASCO C3数据的分析揭示了一个不连续性,解释为一个冲击波,在一个有限的区域内的等离子体密度径向分布在每一个前面的10个选定的日冕物质抛射(CME)沿其行进方向。在各种事件中,冲击波速度为$V\approx$ 800-2500 km s $^{-1}$。将阿尔文马赫数$M_A$对激波强度$ρ_2/ρ_1$的依赖关系(在距太阳中心$R > 10R_\odot$测得)与理想MHD计算进行比较,表明表征激波阵面内部过程的有效绝热指数$γ$在很大程度上介于2和5/3之间。这对应于运动自由度的有效数量2至3。对于地球的弓形激波和行星际无碰撞激波,也导出了类似的依赖关系,即$M_A(ρ_2/ρ_1)$。所有这些都支持了CME前的间断是无碰撞激波的假设。
Quadrature Observations of Wave and Non-Wave Components and Their Decoupling in an Extreme-Ultraviolet Wave Event
我们报告了2011年1月27日极紫外(EUV)波事件的正交观测结果,由极紫外成像仪(EUVI)机载\emph{Solar Terrestrial Relations Observatory}(\emph{STEREO})和大气成像组件(AIA)机载\emph{Solar Dynamics Observatory}(\emph{SDO})。在极紫外波事件中揭示了两个分量。以$\sim$ 440 km s $^{-1}$的初始速度发射主锋。在较热的通道中出现显著的排放增强,而在较冷的通道中出现深度排放减少。当主锋遇到一个大的日冕环系统并减速时,一个次要的更微弱的锋从主锋发出,具有相对较高的$\sim$ 550 km s $^{-1}$的起始速度。之后,两个波前独立地传播,分离度增加。主锋最后停在磁分界线上,而次锋在它消失之前行进得更远。此外,当次级锋到达时,会触发日珥的横向振荡。我们认为这两个组成部分具有不同的性质。主锋属于非波型日冕物质抛射(CME)分量,可以用场线拉伸模型合理解释。这种多温度行为可能是由于CME锋面环的非线性绝热压缩所引起的相当大的加热所造成的。对于次级锋,它很可能是一个线性快模磁流体(MHD)波,通过典型的日冕温度的介质传播。X射线和无线电数据为我们提供了支持上述情况的补充证据。
The kinematics of coronal mass ejections using multiscale methods
日冕物质抛射(CME)的扩散形态和瞬态性质使得它们难以使用传统的图像处理技术进行识别和跟踪。我们应用多尺度方法来增强微弱的日冕物质抛射锋的可见性。这使得椭圆表征能够客观地研究由太阳和日光层天文台(SOHO)上的大角度光谱日冕仪(LASCO)和日地关系天文台(STEREO)上的日地连接日冕和日光层调查(SECCHI)成像的事件样本的变化形态和运动学。这些方法的准确性使我们能够测试CME的非恒定加速和膨胀。我们利用CME的多尺度性质来提取结构与多尺度分解,类似于Canny边缘检测器。时空滤波突出了CME前沿在时间上的传播。我们应用一个椭圆参数化的前提取运动学(高度,速度,加速度)和变化的形态(宽度,方向)。本文讨论的CME的运动学演化与现有的星表不同。这些星表是基于运行差异技术,可能会导致高估日冕物质抛射高度。我们得到的运动学曲线与常加速度模型拟合不好。结果表明,某些事件在$\sim$ 5 R $_{\sun}$以下具有高加速度.此外,我们发现这些星表测量的CME角宽度被高估,事实上,对于某些事件,我们的分析表明CME在整个天空平面上的非恒定扩展。
The detailed observational analysis of a homologous Extreme-ultraviolet (EUV) wave event is presented to study the driving mechanism and the physical property of the EUV waves, combining high resolution data taken by the Solar Dynamics Observatory and the Solar TErrestrial RElations Observatory. It is observed that four homologous EUV waves originated from the same active region AR11476 within about one hour, and the time separations between consecutive waves were of 8 - 20 minutes. The waves showed narrow arc-shaped wavefronts and propagated in the same direction along a large-scale transequa…
Statistical Analysis of Large-scale EUV Waves Observed by STEREO/EUVI
本文对2007年1月至2011年2月期间发生的60次强大尺度极紫外波事件进行了统计分析,分析了它们的运动学演化和波脉冲特征。对于起始速度,我们获得算术平均值$312\pm115$ km s $^{-1}$(在100 $-$ 630 km s $^{-1}$的范围内)。对于平均(线)速度,算术平均值为$254\pm76$ km s $^{-1}$(在130 $-$ 470 km s $^{-1}$的范围内)。在研究的所有波中,有52%的波在传播过程中表现出明显的减速($a\leq-50$ m s $^{-2}$),另外48%的波在不确定性范围内与恒定速度一致($-50\leq a\leq50$ m s $^{-2}$)。起始速度和加速度与$c\approx-0.8$、\textit有很强的相关性,即初始较快的事件比较慢的事件经历更强的减速。之间的(平滑)的过渡发生在EUV波的起始速度为$v\approx230$公里秒$^{-1}$,这对应于快速模式的速度在安静的电晕慢事件和减速的恒定传播。这些发现提供了强有力的证据表明,所研究的EUV波确实是大振幅快模MHD波。这一解释进一步支持的峰值速度和峰值振幅,冲动,和建立时间的干扰之间获得的相关性。我们得到了以下的EUV波事件与其他太阳现象的关联率:95%与日冕物质抛射(CME),74%与太阳耀斑,15%与行星际II型爆发,22%与日冕II型…
Preferential Appearance of H$α$ Moreton Waves along Photospheric Magnetic Network Boundaries
School of Astronomy and Space Science, Nanjing University(南京大学天文与空间科学学院);Key Laboratory for Modern Astronomy and Astrophysics, Nanjing University(南京大学现代天文与天体物理重点实验室);State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology(澳门科技大学月球与行星科学国家重点实验室)
We report the first unambiguous observational evidence in the radio range of the reflection of a coronal shock wave at the boundary of a coronal hole. The event occurred above an active region located at the northwest limb of the Sun and was characterized by an eruptive prominence and an extreme-ultraviolet (EUV) wave steepening into a shock. The EUV observations acquired by the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory(SDO) and the Extreme Ultraviolet Imager (EUVI) instrument on board the Solar TErrestrial RElations Observatory(STEREO-A) were used t…
Solar coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field from the Sun into the corona and interplanetary space. They are the most significant drivers of adverse space weather at Earth and other locations in the heliosphere, so it is important to understand the physics governing their eruption and propagation. However the diffuse morphology and transient nature of CMEs makes them difficult to identify and track using traditional image processing techniques. In this thesis the implementation of multiscale image processing techniques to identify and track the CME…