Siphon flow in a cool magnetic loop
C. Bethge, C. Beck, H. Peter, A. Lagg
我们调查的太阳色球层中的活动区域的结构的属性，以找出是否功能是一致的，在充满色球层材料的磁回路中的虹吸流。
We investigate the properties of a structure in the solar chromosphere in an active region to find out whether the feature is consistent with a siphon flow in a magnetic loop filled with chromospheric material.
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Seismology of transversely oscillating coronal loops with siphon flows
在太阳大气中观测到亚阿尔夫文速度的流动，但在耀斑和日冕物质抛射事件之后，流动可以变成阿尔夫文速度。在这封信中，我们推导出一个表达式的固定扭结模式频率由于虹吸流在日冕循环，有效的低速和高速制度。研究发现，虹吸流沿冠环引入了线性空间相关的相移和非对称的本征函数。我们演示了如何使用这个理论来确定的扭结和流动速度的振荡日冕循环的观测案例研究。结果表明，虹吸流的存在会导致传统地震学方法低估冕环中的磁场强度。
Standing oscillations with multiple periods were found in a number of atmospheric structures on the Sun. The ratio of the period of the fundamental to twice the one of its first overtone, $P_1/2P_2$, is important in applications of solar magneto-seismology. We examine how field-aligned flows impact $P_1/2P_2$ of standing modes in solar magnetic cylinders. For coronal loops, the flow effects are significant for both fast kink and sausage modes. For kink ones, they reduce $P_1/2P_2$ by up to 17\% relative to the static case even when the density contrast between the loop and its surroundings app…
Upflows in funnel-like legs of coronal magnetic loops
Ne viii的显著蓝移与平静太阳中磁网络的连接点有关，这一点仍然没有得到很好的理解。通过比较的日冕磁场结构所获得的位场重建与显着的蓝移补丁的多普勒频移Ne VIII在赤道安静的太阳区域观察到的，我们发现，大多数地区具有显着的上升流与漏斗状的腿的磁环和共空间的线宽的增量。这些准定常上升流可被视为日冕环物质供应的特征。通过使用线强度的平方根作为等离子体密度的代理，可以估计每个漏斗中的上升流的质量通量。我们发现，质量通量是反相关的漏斗的膨胀因子确定从外推的磁场。其中一个环系统与一个日冕亮点有关，它被几种仪器观测到，在不同的波长和观察方向上表现出各种形态。一个显着的协议之间的磁性结构和相关的EUV发射模式被发现，表明一个几乎势场性质的日冕磁场。我们还报告了直接检测的小规模虹吸流的STEREO卫星。然而，这种瞬态虹吸流发生在一个弱的混合极性场区域，这是外相邻的磁漏斗，因此，它可能是不相关的漏斗中的等离子体上升流。基于这些观测结果，我们认为，在上TR温度的主导流在安静的太阳日冕环是持久的上升流，而不是虹吸流。我们还讨论了日冕加热和未解决的磁结构的影响。
We report on the first Interface Region Imaging Spectrograph (IRIS) study of cool transition region loops. This class of loops has received little attention in the literature. A cluster of such loops was observed on the solar disk in active region NOAA11934, in the Si IV 1402.8 Å spectral raster and 1400 Å slit-jaw (SJ) images. We divide the loops into three groups and study their dynamics and interaction. The first group comprises relatively stable loops, with 382--626\,km cross-sections. Observed Doppler velocities are suggestive of siphon flows, gradually changing from -10 km/s at one end t…
We extend our earlier multidimensional, magnetohydrodynamic simulations of coronal rain occurring in magnetic arcades with higher resolution, grid-adaptive computations covering a much longer ($>6$ hour) timespan. We quantify how in-situ forming blob-like condensations grow along and across field lines and show that rain showers can occur in limit cycles, here demonstrated for the first time in 2.5D setups. We discuss dynamical, multi-dimensional aspects of the rebound shocks generated by the siphon inflows and quantify the thermodynamics of a prominence-corona-transition-region like structure…
We present a temperature and a magnetic-field surface map of the K2 subgiant of the active binary II Peg. Employed are high resolution Stokes IV spectra obtained with the new Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT). Our main result is that the temperature features on II Peg closely correlate with its magnetic field topology. We find a warm spot (350K warmer with respect to the effective temperature) of positive polarity and radial field density of 1.1 kG coexisting with a cool spot (780K cooler) of negative polarity of 2 kG. Seve…
Solar low-lying cool loops and their contribution to the transition region EUV output
在过去的30年里，人们提出并讨论了小而冷的磁环（高度< 8 Mm，T < 10^5 K）的存在，以解释向色球层的DEM（差分发射测量）的增加。我们提出了流体动力学模拟的低洼冷回路，研究它们的存在和稳定性的条件，以及它们的过渡区EUV输出的贡献。我们发现，稳定的，准静态的冷却回路（速度< 1公里/秒），可以得到不同的和更现实的假设下的辐射损失函数相对于以前的作品。将这些冷环和温度在10^5 ~ 10^6 K之间的中间环的DEM混合，可以再现在临界温度点（T ~ 2x10^5 K）和低于T = 10^5 K时观察到的下过渡区的发射。
We present an analysis of off-limb cool flare loops observed by SDO/AIA during the gradual phase of SOL2017-09-10T16:06 X8.2-class flare. In the EUV channels starting from the 335 Å one, cool loops appear as dark structures against the bright loop arcade. These dark structures were precisely coaligned (spatially and temporally) with loops observed by SST in emission lines of hydrogen and ionized calcium. Recently published semi-empirical model of cool loops based on SST observations serves us to predict the level of hydrogen and helium recombination continua. The continua were synthesized usin…
Hinode EIS Observations of Plasma Composition Evolution and Radiative Cooling of Solar Flare Loops
Hinode EIS观测揭示太阳耀斑环中等离子体组成变化影响其辐射冷却速率，通过分析不同区域的冷却时间和FIP偏倚差异，揭示了等离子体组成演变对耀斑环动态的潜在影响。
Minimal observational evidence exists for fast transition region (TR) upflows in the presence of cool loops. Observations of such occurrences challenge notions of standard solar atmospheric heating models, as well as their description of bright TR emission. Using the {\it EUV Imaging Spectrometer} (EIS) onboard {\it Hinode}, we observe fast upflows ($v_λ$\,$\le$\,$-$10 km s$^{-1}$) over multiple TR temperatures (5.8\,$\le$\,$\log T$\,$\le$ 6.0) at the footpoint sites of a cool loop ($\log T$\,$\le$\,6.0). Prior to cool loop energizing, asymmetric flows of $+$\,5 km s$^{-1}$ and $-$\,60 km s$^{…
Coronal loops are basic building blocks of solar atmosphere and are observed on various length scales. However, their formation mechanism is still unclear. In this paper, we present the spectroscopic and imaging observations of small-scale transients and subsequent formation of transient loops. For the purpose, we have utilized the multi-wavelength observations recorded by AIA and IRIS-SJI, along with spectroscopic measurements provided by IRIS. For the photospheric magnetic field data, we obtained line-of-sight magnetogram data provided by HMI. Small-scale transients are simultaneously observ…
We observe plasma flows in cool loops using the Slit-Jaw Imager (SJI) onboard the Interface Region Imaging Spectrometer (IRIS). Huang et al. (2015) observed unusually broadened Si IV 1403 angstrom line profiles at the footpoints of such loops that were attributed to signatures of explosive events (EEs). We have chosen one such uni-directional flowing cool loop system observed by IRIS where one of the footpoints is associated with significantly broadened Si IV line profiles. The line profile broadening indirectly indicates the occurrence of numerous EEs below the transition region (TR), while i…
Small-scale Hα Jets in the Solar Chromosphere
利用Dunn太阳望远镜上太阳大气快速振荡多波长成像仪的高时空分辨率观测，研究了正在形成的太阳活动区中小尺度Hα喷流的速度。该数据集包括Hα核心、Ca II K和G波段的同步成像，以及光球视线磁图。时间-距离技术被用来确定投影的天空平面速度。Hα图像本质上是高度动态的，估计喷流速度高达45 km s^{-1}。这些喷流是单向的，它们的起源似乎与潜在的Ca II K增亮和G带磁亮点有关。我们认为冷冕环的虹吸流模型适合于解释我们的观测结果。喷流与小规模的爆炸事件有关，并可能提供从光球到日冕的物质外流。
We investigate the increase of the DEM (differential emission measure) towards the chromosphere due to small and cool magnetic loops (height $\lesssim8$~Mm, $T\lesssim10^5$~K). In a previous paper we analysed the conditions of existence and stability of these loops through hydrodynamic simulations, focusing on their dependence on the details of the optically thin radiative loss function used. In this paper, we extend those hydrodynamic simulations to verify if this class of loops exists and it is stable when using an optically thick radiative loss function. We study two cases: constant backgro…
High speed magnetized flows in the quiet Sun
我们已经研究了这些事件的空间和偏振特性，使用各种数据从日之出航天器。我们还推断了大气层结的物理参数反演的观测斯托克斯轮廓采用斯托克斯反演响应函数（SIR）代码的基础上。最后，我们使用同一仪器的时间序列分析了它们的演变。蓝移事件倾向于出现在颗粒边缘的明亮区域，而红移事件主要出现在颗粒间通道的黑暗区域。在连接它们的区域中可以看到大的线性偏振信号。从时间序列推断的磁性结构显示，该结构对应于一个$Ω$环，一个足点总是在颗粒的边缘和其他内部的粒间巷。从这两个事件中观测到的斯托克斯剖面反演得到的物理参数表明，相对于哈佛-史密斯参考大气，$\logτ_{500} \in (-1, -3)$的温度增加，大气底部的强磁场$B \ge 1$ kG迅速向上减小，直到在$\logτ_{500} \approx -2$消失。在蓝移事件中，视线速度从大气底部的上升流变为大气顶部的下降流。红移事件显示相反的速度分层。视线速度的符号变化发生在磁场为零的相同光学深度处。最好地解释推断的磁场配置和流动运动的物理机制是沿拱形磁通量管的虹吸流。然而，需要进一步的调查，因为虹吸流的预期特征不能明确识别。
The first spectroscopic observations of cool Mg II loops above the solar limb observed by NASA's Interface Region Imaging Spectrograph ({\it IRIS}; \cite{IRIS}) are presented. During the observation period IRIS is pointed off-limb allowing the observation of high-lying loops, which reach over 70~Mm in height. Low-lying cool loops were observed by the {\it IRIS} slit jaw camera for the entire 4 hour observing window. There is no evidence of a central reversal in the line profiles and the Mg II h/k ratio is approximately 2. The Mg II spectral lines show evidence of complex dynamics in the loops …
We study the dynamics of low-lying cool loop systems for three datasets as observed by the Interface Region Imaging Spectrograph (IRIS). Radiances, Doppler shifts and line widths are investigated in and around observed cool loop systems using various spectral lines formed between the photosphere and transition region (TR). Footpoints of the loop threads are either dominated by blueshifts or redshifts. The co-spatial variation of velocity above the blue-shifted footpoints of various loop threads shows a transition from very small upflow velocities ranging from (-1 to +1) km/s in the Mg\,{\sc ii…
Influence of Cross-sectional Expansion on Coronal Emissions from a Radiatively Cooling Solar Flare Loop
研究横截面扩张对太阳耀斑环日冕辐射的影响，发现其能有效抑制环状结构材料流失并改变辐射输出温度分布。
Flare loops form an integral part of eruptive events, being detected in the range of temperatures from X-rays down to cool chromospheric-like plasmas. While the hot loops are routinely observed by the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA), cool loops seen off-limb are rare. In this paper we employ unique observations of the SOL2017-09-10T16:06 X8.2-class flare which produced an extended arcade of loops. The Swedish 1-m Solar Telescope (SST) made a series of spectral images of the cool off-limb loops in the Ca II 8542 Å and the hydrogen H$β$ lines. Our focus is on …
How the solar corona is heated to high temperatures remains an unsolved mystery in solar physics. In the present study we analyse observations of 50 whole active-region loops taken with the Extreme-ultraviolet Imaging Spectrometer (EIS) on board the Hinode satellite. Eleven loops were classified as cool (<1 MK) and 39 as warm (1-2 MK) loops. We study their plasma parameters such as densities, temperatures, filling factors, non-thermal velocities and Doppler velocities. We combine spectroscopic analysis with linear force-free magnetic-field extrapolation to derive the three-dimensional structur…
The evolution of a coronal loop is studied by means of numerical simulations of the fully compressible three-dimensional magnetohydrodynamic equations using the HYPERION code. The footpoints of the loop magnetic field are advected by random motions. As a consequence the magnetic field in the loop is energized and develops turbulent nonlinear dynamics characterized by the continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Dissipation is non-uniformly distributed so that only a fraction of the coronal mass and volume ge…
Continuous upflows and sporadic downflows observed in active regions
我们提出了一个研究的时间演化的日冕循环在活动区和它的影响，在日冕循环的动力学。我们分析了太阳动力学天文台（SDO）上的大气成像组件（AIA）在多种温度下的图像，以检测日冕环中的视运动。准周期性的亮度波动向上传播的循环足迹在热发射在1MK，而零星的下行流被认为是在冷发射低于1MK。热辐射的上升运动在冷的下降流之后增加。表面的传播模式表明，从环足点的热上升流，并被认为是供应热等离子体进入日冕环，但波状现象不能被排除。日冕环中偶而发生日冕凝结，冷物质向下流动到足点。冷等离子体的发射可能有显着的贡献，热AIA通道在日冕凝结的事件。
The variation of the vector magnetic field along structures in the solar corona remains unmeasured. Using a unique combination of spectropolarimetry and stereoscopy, we infer and compare the vector magnetic field structure and three-dimensional morphology of an individuated coronal loop structure undergoing a thermal instability. We analyze spectropolarimetric data of the He I 10830 Å triplet ($1s2s{\ }^{3}S_{1} - 1s2p{\ }^{3}P_{2,1,0}$) obtained at the Dunn Solar Telescope with the Facility Infrared Spectropolarimeter on 19 September 2011. Cool coronal loops are identified by their prominent …
Extreme UV (EUV) and X-ray loops in the solar corona connect regions of enhanced magnetic activity, but they are not usually rooted in the dark umbrae of sunspots because the strong magnetic field found there suppresses convection. This means that the Poynting flux of magnetic energy into the upper atmosphere is not significant within the umbra as long as there are no light bridges or umbral dots. Here we report a rare observation of a coronal loop rooted in the dark umbra of a sunspot without any traces of light bridges or umbral dots. We used the slit-jaw images and spectroscopic data from I…
Solar filaments can be formed via chromospheric evaporation followed by condensation in the corona or by the direct injection of cool plasma from the chromosphere to the corona. In this paper, with high-resolution H$α$ data observed by the 1.6 m New Solar Telescope of the Big Bear Solar Observatory on 2015 August 21, we confirmed that an active-region filament is maintained by the continuous injection of cold chromospheric plasma. We find that the filament is rooted along a bright ridge in H$α$, which corresponds to the intersection of a magnetic quasi-separatrix layer with the solar surface. …
We present the properties of the inverse Evershed flow (IEF) based on the center-to-limb variation of the plasma speed and loop geometry of chromospheric superpenumbral fibrils in eleven sunspots that were located at a wide range of heliocentric angles from 12 to 79 deg. The observations were acquired at the Dunn Solar Telescope in the spectral lines of Halpha at 656nm, CaII IR at 854 nm and HeI at 1083 nm. All sunspots display opposite line-of-sight (LOS) velocities on the limb and center side with a distinct shock signature near the outer penumbral edge. We developed a simplified flexible su…
Theoretical Models of Sunspot Structure and Dynamics
综述了太阳黑子理论模拟的最新进展。在垂直的单片磁场中的磁对流的现实模拟很好地再现了本影点的观察到的属性。为了理解半影，区分内半影和外半影是很有用的，内半影主要由包含细长暗核的亮丝组成，外半影由宽度相当的暗丝和亮丝组成，相应的磁场倾角相差约30度，暗丝中沿着几乎水平或向下倾伏的磁场有强的埃弗谢德流。通过数值实验研究了磁通量泵在外半影淹没磁通量中的作用，并根据高分辨率观测结果讨论了半影磁场的不同几何模型。最近，现实的数值MHD模拟的整个太阳黑子已经成功地再现的本影和内半影的对流模式的显着特点。虹吸流动机制仍然是埃弗谢德流动的最好解释，特别是在外部半影区，那里通常由冷的超音速下降流组成。
Observations of the Formation and Disappearance of a Funnel Prominence
本文观测研究了漏斗状日珥的形成与消失过程，发现色球等离子体被输送至日冕腔后经垂直下降流排出可形成漏斗状日珥，揭示了其演化受磁重联及物质流动驱动。
Enhanced Peak and Extended Cooling of the Extreme-ultraviolet Late Phase in a Confined Solar Flare
研究分析一次X1.8非爆发性太阳耀斑，提出磁通量绳失败爆发加热及环截面随高度扩张机制，解释EUV晚期相的增强峰值与延长冷却。
Slow magnetosonic waves and fast flows in active region loops
最近的EUV光谱观测表明，慢磁声波存在于活动区（AR）环路。一些光谱数据也被解释为快速（~100-300 km/s）准周期流动的证据。我们已经进行了三维磁流体动力学（3D MHD）建模的双极AR，其中包含脉冲产生的波和流动的日冕循环。AR模型是由偶极磁场和重力分层密度开始的，在磁环的足点处的局部区域中稳定地或周期性地驱动上升流。通过将材料注入通量管并建立虹吸流，沿AR的磁场线产生的流与周围等离子体相比产生更高密度的回路。我们发现，与亚声速的流动的冲击开始的结果在阻尼慢磁声波的激励，沿环路传播和耦合的非线性驱动的快模式波。慢磁声波的相速度接近日冕声速。当驱动脉冲的振幅增加时，我们发现产生了慢激波状的波列。当周期性地驱动上升流时，产生无阻尼振荡，其周期由上升流的周期性确定。基于三维MHD模型的结果，我们认为观测到的慢磁声波和持续上升流可能是由同一脉冲事件在AR的底部产生的。
EUV imaging observations from several space missions (SOHO/EIT, TRACE, and SDO/AIA) have revealed a presence of propagating intensity disturbances in solar coronal loops. These disturbances are typically interpreted as slow magnetoacoustic waves. Recent spectroscopic observations with Hinode/EIS of active region loops, however, revealed that the propagating intensity disturbances are associated with intermittent plasma upflows (or jets) at the footpoints which are presumably generated by magnetic reconnection. For this reason, whether these disturbances are waves or periodic flows is still bei…
We report on the first direct observation of a fast-mode wave propagating along and perpendicular to cool (171 Å) arcade loops observed by the SDO/AIA. The wave was associated with an impulsive/compact flare, near the edge of a sunspot. The EUV wavefront expanded radially outward from the flare center and decelerated in the corona from 1060-760 km/s within ~3-4 minute. Part of the EUV wave propagated along a large-scale arcade of cool loops and was partially reflected back to the flare site. The phase speed of the wave was about 1450 km/s, which is interpreted as a fast-mode wave. A second ove…
We present the observations of a blowout jet that experienced two distinct ejection stages. The first stage started from the emergence of a small positive magnetic polarity, which cancelled with the nearby negative magnetic field and caused the rising of a mini-filament and its confining loops. This further resulted in a small jet due to the magnetic reconnection between the rising confining loops and the overlying open field. The second ejection stage was mainly due to the successive removal of the confining field by the reconnection. Thus that the filament erupted and the erupting cool filam…
Spectroscopic Diagnostic of the Footpoints of the Cool loops
本文利用IRIS的Si IV谱线诊断冷环足点，发现β-γ活动区足点的强度、FWHM和光谱复杂度均高于β活动区，且超过半数足点位置受不透明度或共振散射影响，揭示两类活动区足点性质显著不同。
Active region transition region loop populations and their relationship to the corona
不同温度下冕环结构之间的关系尚未确定。先前的研究表明，在活动区域的核心，日冕环不会通过较低的温度冷却，因此会稳定地加热。如果环是冷却的，过渡区将是一个理想的温度制度，以寻找其演变的签名。日出号上的极紫外成像光谱仪（EIS）以前所未有的节奏和空间分辨率提供太阳过渡区和日冕的单色图像，使其成为揭示这一问题的理想仪器。对2007年12月8 - 19日活动区10978的观测分析表明，活动区存在两种主要的环群：核心多温环，在0.4 - 2.5MK甚至更高的温度范围内经历连续的加热和冷却过程，如X射线望远镜（XRT）所示;以及主要在0.4 - 1.3MK温度范围内演化的外围环。在过渡区温度的环可以达到150毫米的高度，在冠以上的肢体和发展下降流的速度在39 - 105公里/秒的范围内。
Recent observations in extreme-ultraviolet (EUV) wavelengths reveal an EUV late phase in some solar flares that is characterized by a second peak in warm coronal emissions ($\sim3$~MK) several tens of minutes to a few hours after the soft X-ray (SXR) peak. Using the model enthalpy-based thermal evolution of loops (EBTEL), in this paper we numerically probe the production of EUV late-phase solar flares. Starting from two main mechanisms of producing the EUV late phase, i.e., long-lasting cooling and secondary heating, we carry out two groups of numerical experiments to study the effects of thes…
We report on the properties of coronal loop foot-point heating with observations at the highest resolution, from the CRisp Imaging Spectro-Polarimeter (CRISP) located at the Swedish 1-m Solar Telescope (SST) and co-aligned NASA Solar Dynamics Observatory (SDO) observations, of Type II spicules in the chromosphere and their signatures in the EUV corona. Here, we address one important issue, as to why there is not always a one-to-one correspondence, between Type II spicules and hot coronal plasma signatures, i.e. beyond TR temperatures. We do not detect any difference in their spectral propertie…
Velocity measurements for a solar active region fan loop from Hinode/EIS observations
利用Hinode卫星上的极紫外成像光谱仪（EIS）的数据，推导出温度范围为0.15-1.5 MK的太阳活动区内的风扇环结构的速度模式。该环与观测者的视线对齐，并显示出约15 km/s的下降流（红移），温度高达0.8 MK，但对于1.0 MK及以上的温度，测量的速度变化与无净流一致。这个速度的结果适用于在一个投影的空间距离为9毫米，并表明，较冷，红移等离子体是物理断开的较热，静止等离子体。一个方案中，风扇回路包括至少两组的“股”-一个冷却器和向下流动，其他热和固定-建议。较冷的股线可能代表较热的股线的后期进化阶段。Mg VII的密度诊断显示，在0.8 MK附近，电子密度从环底部的3.2 x 10^9 cm^-3下降到投影高度为15 μ m时的5.0 x 10^8 cm^-3。在接近Mg VII形成温度的温度下，填充因子为0.2（0.8 MK），证实了较冷的，向下流动的等离子体仅占表观回路体积的一小部分。扇形环的根源是一个所谓的“外流区”，在Fe XII 195.12 A（形成于1.5 MK）中显示出低强度和高达25 km/s的蓝移，而在0.8 MK时环的红移为15 km/s。一种新的技术，用于获得绝对波长校准的EIS仪器和仪器的影响，可能与一个扭曲的点扩散函数，影响速度测量被确定。
A three-dimensional view of the thermal structure in a super-penumbral canopy
我们通过确定活动区域的三维热结构来研究超半影冠层的热拓扑。我们推导出的温度分层在活性区域的钙II IR线在854.2 nm的反转，假设LTE。我们跟踪的3D拓扑结构的个人功能位于超级半影冠层，主要是径向定向的原纤维。我们发现，大约有一半的原纤维形成短，拱形，低洼的温度立方体环。这些闭合的环从半影中或接近半影的明亮颗粒连接到距离太阳黑子几毫米远的光球。它们的高度不到1毫米。另一半的纤维上升与距离太阳黑子，直到他们离开钙II IR形成的高度。许多原纤维显示一个中央暗核和两个侧面增亮，如线核强度图像所示。相应的速度图像显示了与在强度上看到的原纤维一样宽的原纤维，而没有横向子结构。此外，我们更详细地研究了一个异常亮度的例子。它属于另一类结构，没有突出的质量流，并具有由两个平行的闭合回路连接相反极性的斑块形成的3D拓扑结构。我们提出的证据表明，逆Evershed流到太阳黑子在较低的色球层的虹吸流沿短循环连接光球脚点的后果。色球纤维的暗核结构不可能有对流起源，因为它们位于光学薄大气中的规则颗粒之上。暗芯最有可能是由沿原纤维的显著流速引起的中心轴和侧边缘之间的不透明度差异引起的。
Coronal fuzziness modelled with pulse-heated multistranded loop systems
观测到日冕活动区在越来越硬的能带或谱线中变得越来越模糊（即越来越混乱和均匀）。我们解释这一证据是由于精细的多温度结构的日冕环。为此，我们建立了由细线组成的环束模型，每个环束都由短而强的热脉冲加热。为了简单起见，我们假设热脉冲都是相等的，并且在随机时间在每条链中仅触发一次。选择脉冲强度和节奏，以便平均具有稳定的活性区环（$\sim 3$ MK）。我们用流体力学环模型计算了受限加热等离子体的演化。然后，我们计算沿着每条链的几条谱线的发射，从冷（$\leq 1$ MK）到暖（$2-3$ MK）线，用Hinode/EIS检测到热X射线线。然后将这些链并排放置以构建活性区环束。我们发现，在温暖的线（$2-3$ MK）的循环发射填充所有可用的图像表面。因此，发射看起来相当均匀，很难分辨单个环，而在冷线中，环的对比度要高得多，区域也不那么模糊。这种效应的主要原因是，在它们的演变过程中，即脉冲加热和缓慢冷却，每条线在$2-3$ MK附近的温度下花费相对较长的时间，并且在该阶段期间具有高发射测量，因此整个区域看起来更均匀或模糊。我们预测，在热的紫外线和X射线谱线中，富勒烯应该减少。
Employing Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) multi-wavelength images, we report the coronal condensation during the magnetic reconnection (MR) between a system of open and closed coronal loops. Higher-lying magnetically open structures, observed in AIA 171 A images above the solar limb, move downward and interact with the lower-lying closed loops, resulting in the formation of dips in the former. An X-type structure forms at the interface. The interacting loops reconnect and disappear. Two sets of newly-reconnected loops then form and recede from the MR region.…
Spectroscopic Observations of Coronal Rain Formation and Evolution following an X2 Solar Flare
本文报告了Hinode/EIS对X2.1耀斑后日冕雨形成与演化的罕见光谱观测，通过等离子体成分、非热速度和多普勒测量揭示了凝结演化过程，为日冕加热率与日冕雨集体行为提供了见解。
Catastrophic cooling and cessation of heating in the solar corona
在极紫外线（EUV）下，通常可以观察到温度超过10^6 K的太阳热日冕中的凝聚。虽然它们对太阳EUV总辐射的贡献仍然是一个有争议的问题，但这些凝结无疑为研究日冕对加热过程的动态响应提供了一个有价值的工具。我们研究了不同的能量输入在时间和空间上的分布，以研究哪个过程与理解这些日冕凝聚最相关。为了与观测结果进行比较，我们从一个随时间变化的一维模型中合成了EUV辐射，其中我们采用了两种加热方案：简单地关闭加热和加热非常集中在循环足点的模型，同时保持总热输入恒定。加热关/开模型不会导致使用SDO/AIA观察到的显著EUV计数率。相比之下，足点附近的加热集中导致环路顶部附近的热不平衡，从而导致众所周知的灾难性冷却。这一过程与日冕凝聚的观测结果非常吻合。这表明日冕需要稳定的能量供应来支持日冕等离子体，即使在日冕凝聚期间。否则，电晕会非常快地流失，太快了，甚至不能形成冷凝。
Solar Dynamics Observatory discovers thin high temperature strands in coronal active regions
一种解释百万度太阳日冕的方案是一种精细的日冕，其中每一股都被快速脉冲加热。然而，这样的精细结构既没有通过直接成像观测解决，也没有通过扩展的超热等离子体的间接观测得出结论。最近已经表明，观察到的冷和暖日冕环（分别为~1 MK，~2-3 MK）的外观差异-暖环比冷环看起来“模糊”-可以用亚弧秒链组成的环模型来解释，这些环被脉冲加热到~10 MK。这项工作预测，热日冕环（>~6 MK）的图像应该再次显示出精细的结构。在这里，我们表明，预测的效果确实被广泛观察到在一个活跃的区域与太阳动力学天文台，从而支持的情况下，脉冲加热的细环股在供电的活动日冕中发挥着重要作用。
Elemental Composition Evolution during the 2024 September 30 Solar Eruption: A Comparison of Hot and Cool Plasma Components with Solar Orbiter/SPICE, Hinode/EIS, and Chandrayaan-2/XSM
该研究利用Solar Orbiter、Hinode、Chandrayaan-2的相关仪器，观测2024年9月30日M7.6级太阳耀斑，发现高低温等离子体成分丰度演化模式不同，揭示了FIP偏差变化与日冕重联外流和色球层等离子体混合相关的机制。
Constraints on the Heating of High Temperature Active Region Loops: Observations from Hinode and SDO
我们目前的观测高温辐射的核心太阳活动区使用的仪器日出和SDO。这些多仪器观测使我们能够确定等离子体温度的分布，并跟踪不同温度下发射的演变。我们发现，在高温环的顶点处，发射测量分布在4 MK附近强烈达到峰值，并且在较高和较低的温度下急剧下降。也许最重要的是，在0.5 MK的发射测量从在4 MK的峰值减少了两个以上的数量级。我们还发现，在宽波段软X射线图像的时间演变是相对恒定的约6小时的观察。在较冷的SDO/AIA带通中的观测通常不显示活动区核心中的冷却回路，这与在高温下观测到的稳定发射一致。这些观测结果表明，在活动区核心观测到的高温环接近平衡。我们发现，这是可能的，以重现一个简单的，高频加热的情况下，加热事件发生的时间尺度远小于冷却时间的高温发射线的相对强度。相比之下，低频加热的情况下，这通常被调用来描述日冕加热的纳米耀斑模型，不再现高温发射线的相对强度和预测的低温发射，大约是一个数量级太大。我们还提出了一个初步的图像从SDO/AIA 94 A通道，这是敏感的Fe XVIII。
On the Nature of the Extreme-Ultraviolet Late Phase of Solar Flares
太阳耀斑的极紫外（EUV）晚期是暖日冕发射的第二个峰值（例如，Fe XVI）在GOES软X射线峰之后的许多分钟到几个小时。它首先由太阳动力学天文台（SDO）上的EUV变率实验（EVE）观测到。晚相发射源自第二组较长的环（晚相环），其高于主耀斑环。它被认为是由额外的加热或长期冷却引起的。在本文中，我们研究的作用，长期持续的冷却和额外的加热在产生EUV后期使用“基于循环的热演化”（EBTEL）模型。我们发现，一个长期的冷却过程中的后期阶段环路可以很好地解释的EUV后期阶段发射的存在，但我们不能排除在衰变阶段的额外加热的可能性。此外，我们提供了两个初步的方法的基础上的紫外线和极紫外线发射的大气成像组件（AIA）上SDO，以确定是否有额外的加热发挥一定的作用或没有在后期阶段的排放。利用非线性无力场模型，我们研究了极紫外后期的磁位形。研究发现，晚相既可以在与磁零点相关联的热脊磁力线中产生，也可以在多极磁场的大尺度磁环中产生。在本文中，我们还讨论了为什么在暖日冕辐射中通常观察到EUV晚期相，以及为什么大多数耀斑不表现出EUV晚期相。
Employing Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) multi-wavelength images, we have presented coronal condensations caused by magnetic reconnection between a system of open and closed solar coronal loops. In this Letter, we report the quasi-periodic fast magnetoacoustic waves propagating away from the reconnection region upward across the higher-lying open loops during the reconnection process. On 2012 January 19, reconnection between the higher-lying open loops and lower-lying closed loops took place, and two sets of newly reconnected loops formed. Thereafter, cooling and…
New and advanced space-based observing facilities continue to lower the resolution limit and detect solar coronal loops in greater detail. We continue to discover even finer sub-structures within coronal loop cross sections, in order to understand the nature of the solar corona. Here, we push this lower limit further to search for the finest coronal loop sub-structures, through taking advantage of the resolving power of the Swedish 1- m Solar Telescope (SST) / CRisp Imaging Spectro-Polarimeter (CRISP), together with co-observations from the Solar Dynamics Observatory (SDO) / Atmospheric Image …
We intend to investigate the underlying physics for the coronal rain phenomenon in a representative bipolar magnetic field, including the formation and the dynamics of coronal rain blobs. With the MPI-AMRVAC code, we performed three dimensional radiative magnetohydrodynamic (MHD) simulation with strong heating localized on footpoints of magnetic loops after a relaxation to quiet solar atmosphere. Progressive cooling and in-situ condensation starts at the loop top due to radiative thermal instability. The first large-scale condensation on the loop top suffers Rayleigh-Taylor instability and bec…
The Neutron star Interior Composition ExploreR (NICER) X-ray observatory observed two powerful X-ray flares equivalent to superflares from the nearby young solar-like star, kappa1 Ceti, in 2019. NICER follows each flare from the onset through the early decay, collecting over 30 cts s-1 near the peak, enabling a detailed spectral variation study of the flare rise. The flare in September varies quickly in ~800 sec, while the flare in December has a few times longer timescale. In both flares, the hard band (2-4 keV) light curves show typical stellar X-ray flare variations with a rapid rise and sl…
Can Thermal Nonequilibrium Explain Coronal Loops?
任何成功的日冕环模型都必须解释许多观测到的性质。对于暖循环（~ 1 MK），这些包括：1.过剩密度，2.平坦的温度曲线，3.超流体静力学尺度高度，4.非结构化强度分布，和5. 1000--5000 s寿命。我们研究是否热不平衡可以重现的意见进行流体动力学模拟的基础上稳定的日冕加热，随高度呈指数下降。我们考虑单片和多股循环。这些模拟成功地再现了观测结果的某些方面，包括超额密度，但每一个都至少在一个关键方面失败了。整体模型有太多的强度结构，而多链模型要么太结构化，要么太长寿。我们的研究结果似乎排除了广泛存在的加热，这是高度集中的低日冕和稳定或准稳定（缓慢变化或脉冲与快速节奏）。如果主要的加热机制具有这些性质，那么活跃区域将具有非常不同的外观。然而，热不平衡可能在连续性和灾难性冷却事件中起重要作用（例如，日冕雨）占据了日冕体积的一小部分。然而，模型和冷却事件观测之间的明显不一致还有待理解。
Analysis of the Stellar Occultations During the Unprecedented Long-Duration Flare
该研究分析年轻主序星27小时超级耀斑中的多次掩星，重建冷耀斑环拱的几何与物理参数，首次在太阳以外恒星上证实此类遮蔽结构。
We investigate intensity variations and energy deposition in five coronal loops in active region cores. These were selected for their strong variability in the AIA/SDO 94 Å intensity channel. We isolate the hot Fe XVIII and Fe XXI components of the 94 Å and 131 Å by modeling and subtracting the "warm" contributions to the emission. HMI/SDO data allow us to concentrate on "inter-moss" regions in the loops. The detailed evolution of the inter-moss intensity time series reveals loops that are impulsively heated in a mode compatible with a nanoflare storm, with a spike in the hot 131 Å signals lea…
Evidence for Widespread Cooling in an Active Region Observed with the SDO Atmospheric Imaging Assembly
离散日冕环的EUV光曲线的公知行为是较冷通道或谱线的峰值强度在比较热通道逐渐晚的时间达到。这种时间滞后被理解为是热日冕环等离子体通过这些较低的各自温度冷却的结果。然而，环通常仅包括有源区中的总发射的一小部分。这种冷却模式是活动区日冕等离子体的共同特性，还是只发生在独特的环境、地点和时间？SDO/AIA的新数据为系统地回答整个活跃地区的这个问题提供了一个极好的机会。我们使用2010年6月19日观测到的AR 11082的24小时图像测量SDO/AIA EUV通道对之间的时间滞后。我们发现，有一个时间滞后的信号与冷却等离子体一致，就像通常发现的环路，在整个活动区域，包括整个24小时的持续时间之间的环路的扩散发射。在24小时的时间段内，对于所有通道对和窗口长度的选择，该模式始终保持不变，这使我们相信等离子体正在从大于3 MK的温度冷却，有时超过7 MK，降至低于~ 0.8 MK的温度。这表明，在这个活跃区域中，大量的日冕等离子体发射并不稳定;相反，它是动态的，不断演变。这些测量为任何试图描述日冕加热的模型提供了关键的限制。
Asymmetries of solar coronal extreme ultraviolet emission lines
在电晕中形成的发射线的轮廓包含关于热等离子体的动力学和加热的信息。直到最近，才有足够高的光谱分辨率的数据可以用来研究远高于10^6 K时所形成的发射线轮廓的细节。这些显示了线翼中的增强发射，这还没有被理解。用多高斯拟合方法研究了日本日出太阳空间天文台极紫外成像光谱仪（EIS）在2.5MK下观测到的Fe XV谱线轮廓，重点研究了谱线宽度和多普勒频移。在活性区的主要部分，光谱最好由窄线芯和宽次要组分拟合。后者约占总排放量的10%至20%，比核心宽约2倍，并显示出高达50 km/s的强烈蓝移。平均而言，对于两个组件，线宽从足迹到循环顶部增加。在较小的限制区域中也可以发现具有高上升速度的组件。日冕结构包括至少两个类，这两个类不能在空间上分辨，而只能在光谱上分辨，并且与线核和次要成分有关。由于其巨大的线宽和强大的上升流，它提出的加热和质量供应的日冕的主要部分实际上是位于源区域的次要组成部分。虹吸流和排水回路中看到的线核心组件是一致的结构中发现的三维MHD日冕模型。尽管在过渡区线中看到的大活动区日冕和小网络元素的外观完全不同，但两者都显示出相似的线轮廓特征。这表明，相同的过程控制着过渡区和日冕的加热和动力学。
The plasma contributing to emission from the Sun between the cool chromosphere ($\le 10^4$K) and hot corona ($\ge 10^6$K) has been subjected to many different interpretations. Here we look at the magnetic structure of this transition region (TR) plasma, based upon the implications of CLASP2 data of an active region recently published by Ishikawa et al., and earlier IRIS and SDO data of quiet regions. Ishikawa et al. found that large areas of sunspot plages are magnetically unipolar as measured in the cores of \ion{Mg}{2} resonance lines, formed in the lower transition region under low plasma-$…
Quasi-constant heating at the footpoints of loops leads to evaporation and condensation cycles of the plasma: thermal non-equilibrium (TNE). This phenomenon is believed to play a role in the formation of prominences and coronal rain. However, it is often discarded to be involved in the heating of warm loops as the models do not reproduce observations. Recent simulations have shown that these inconsistencies with observations may be due to oversimplifications of the geometries of the models. In addition, our recent observations reveal that long-period intensity pulsations (several hours) are co…
The Enthalpy Based Thermal Evolution of Loops (EBTEL) approximate model for static and dynamic coronal loops is developed to include the effect of a loop cross-sectional area which increases from the base of the transition region (TR) to the corona. The TR is defined as the part of a loop between the top of the chromosphere and the location where thermal conduction changes from an energy loss to an energy gain. There are significant differences from constant area loops due to the manner in which the reduced volume of the TR responds to conductive and enthalpy fluxes from the corona. For static…
In solar filament formation mechanisms, magnetic reconnection between two sets of sheared arcades forms helical structures of the filament with numerous magnetic dips, and cooling and condensation of plasma trapped inside the helical structures supply mass to the filament. Although each of these processes, namely, magnetic reconnection and coronal condensation have been separately reported, observations that show the whole process of filament formation are rare. In this Letter, we present the formation of a sigmoid via reconnection between two sets of coronal loops, and the subsequent formatio…
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