Recently solar flares exhibiting a double J-shaped ribbons in the lower solar atmosphere have been paid increasing attention in the context of extending the two-dimensional standard flare model to three dimensions, as motivated by the spatial correlation between photospheric current channels and flare ribbons. Here we study the electric currents through the photospheric area swept by flare ribbons (termed synthesized ribbon area or SRA), with a sample of 71 two-ribbon flares, of which 36 are J-shaped. Electric currents flowing through one ribbon are highly correlated with those through the other, therefore belonging to the same current system. The non-neutrality factor of this current system is independent of the flare magnitude, implying that both direct and return currents participate in flares. J-shaped flares are distinct from non-J-shaped flares in the following aspects: 1) Electric current densities within J-shaped SRA are significantly smaller than those within non-J-shaped SRA, but J-shaped SRA and its associated magnetic flux are also significantly larger. 2) Electric currents through SRA are positively correlated with the flare magnitude, but J-shaped flares show stronger correlation than non-J-shaped flares. 3) The majority (75\%) of J-shaped flares are eruptive, while the majority (86\%) of non-J-shaped flares are confined; accordingly, hosting active regions of J-shaped flares are more likely to be sigmoidal than non-J-shaped flares. Thus, J-shaped flares constitute a distinct subset of two-ribbon flares, probably the representative of eruptive ones. Further, we found that combining SRA and its associated magnetic flux has the potential to differentiate eruptive from confined flares.
Evolution of Spatial Complexity in Flare Ribbon Substructure and Its Relationship to Magnetic Reconnection Dynamics
University of Colorado Boulder（科罗拉多大学博尔德分校）；National Solar Observatory（国家太阳观测台）；Catholic University of America（美利坚天主教大学）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Predictive Science Inc.（预测科学公司）
Statistical Properties of Ribbon Evolution and Reconnection Electric Fields in Eruptive and Confined Flares
本文对H $α$双带耀斑色球带演化进行了统计研究。该数据集由2000年6月至2015年6月发生的50次局限（$62\,\%$）和喷发（$38\,\%$）耀斑组成。耀斑是均匀地选择在H $α$和$\textit{GOES}$（地球同步业务环境卫星）类，重点是包括强大的封闭耀斑和弱喷发耀斑。Kanzelhöhe天文台的H $α$滤波图与$\textit{MDI}$（迈克尔逊多普勒成像仪）和$\textit{HMI}$（日震和磁成像仪）磁图相结合，用于推导带分离、带分离速度、磁场强度和重联电场。我们发现，爆发耀斑揭示统计更大的带状分离和更高的带状分离速度比密闭耀斑。此外，带状分离的爆发耀斑与GOES SXR通量，而没有明确的依赖被发现为封闭的耀斑。最大的带状分离速度与GOES通量没有相关性，但爆发耀斑揭示了平均更高的带状分离速度（由$\approx 10~$ km $~$ s $^{-1}$）。局限耀斑（$cc=0.50~\pm~0.02$）和爆发耀斑（$cc=0.77~\pm~0.03$）的局部重联电场与GOES通量相关，表明更强大的耀斑涉及更强的重联电场。此外，具有更高电场强度的爆发耀斑往往伴随着更快的日冕物质抛射。
Observations of solar flare ribbons show significant fine structure in the form of breaking wave-like perturbations and spirals. The origin of this structure is not well understood, but one possibility is that it is related to the tearing instability in the flare current sheet. Here we study this connection by constructing an analytical three-dimensional magnetic field representative of an erupting flux rope with a flare current sheet below it. We introduce small-scale flux ropes representative of those formed during a tearing instability in the current layer, and use the squashing factor on t…
The presence of current sheet instabilities, such as the tearing mode instability, are needed to account for the observed rate of energy release in solar flares. Insights into these current sheet dynamics can be revealed by the behaviour of flare ribbon substructure, as magnetic reconnection accelerates particles down newly reconnected field lines into the chromosphere to mark the flare footpoints. Behaviour in the ribbons can therefore be used to probe processes occurring in the current sheet. In this study, we use high-cadence (1.7 s) IRIS Slit Jaw Imager observations to probe for the growth…
We analyze high-cadence vector magnetograms (135~s) and flare-ribbon observations of 37 flares from the Solar Dynamics Observatory to understand the spatial and temporal properties of changes in the photospheric vector magnetic field and their relationship to footpoints of reconnected fields. Confirming previous studies, we find that the largest permanent changes in the horizontal field component lie near the polarity inversion line, whereas changes in the vertical field are less pronounced and are distributed throughout the active region. We find that pixels swept up by ribbons do not always …
In this article, we measure the mean magnetic shear from the morphological evolution of flare ribbons, and examine the evolution of flare thermal and non-thermal X-ray emissions during the progress of flare reconnection. We analyze three eruptive flares and three confined flares ranging from GOES class C8.0 to M7.0. They exhibit well-defined two ribbons along the magnetic polarity inversion line (PIL), and have been observed by the Atmospheric Imaging Assembly and the Ramaty High Energy Solar Spectroscopic Imager from the onset of the flare throughout the impulsive phase. The analysis confirms…
Rapid increase of horizontal magnetic field ($B_h$) around the flaring polarity inversion line is the most prominent photospheric field change during flares. It is considered to be caused by the contraction of flare loops, the details behind which is still not fully understood. Here we investigate the $B_h$-increase in 35 major flares using HMI high-cadence vector magnetograms. We find that $B_h$-increase is always accompanied by the increase of field inclination. It usually initiates near the flare ribbons, showing step-like change in between the ribbons. In particular, its evolution in early…
Lower atmospheric lines show peculiar profiles at the leading edge of ribbons during solar flares. In particular, increased absorption of the BBSO/GST \hei~10830~Å line \citep[e.g.][]{Xu2016}, as well as broad and centrally reversed profiles in the spectra of the \mgii~and \cii~lines observed by the \iris~satellite \citep[e.g.][]{Panos2018,Panos2021a} have been reported. In this work, we aim to understand the physical origin of the \iris\ ribbon front line profiles, which seem to be common of many, if not all, flares. To achieve this, we quantify the spectral properties of the \iris~\mgii~ribb…
Flare Ribbons Approach Observed by the Interface Region Imaging Spectrograph and the Solar Dynamics Observatory
我们报告了2015年11月4日在NOAA AR 12443中的多带M级耀斑期间的耀斑带接近（FRA），由界面区域成像光谱仪和太阳动力学观测台获得。耀斑由一对主带和两对次带组成。这两对次级带的形成晚于主带的出现，分别延迟了15分钟和19分钟。负极性的主带比在其前面的具有相同极性的第一次级带更快地向外扩展，因此产生了FRA。就在他们相遇之前，主带急剧变暗，其强度在2分钟内下降了约70%，这意味着产生两个主带的主相重联被抑制。FRA导致主带向副带方向偏转，偏转角约为60度。大约2分钟后形成了后接近拱廊，并沿新拱廊检测到速度为35-40 km/s的下降流，表明FRA过程中的磁重组。我们认为，有三个拓扑结构域的足迹概述的三对丝带。这些域的紧密接近导致与磁场拓扑一致的带的偏转。
Automatic detection of Flare Ribbon Fine Structures as Proxies for Plasmoid Dynamics in Flare Reconnection
Department of Mathematical Sciences, Durham University（达勒姆大学数学科学系）；Heliophysics Science Division, NASA Goddard Space Flight Center（NASA戈达德太空飞行中心日球物理学部）；Astronomy Department, University of Maryland, College Park（马里兰大学天文学系）；Scottish Universities Physics Alliance, School of Physics and Astronomy, University of Glasgow（格拉斯哥大学物理与天文学学院苏格兰大学物理联盟）；Rosseland Centre for Solar Physics, University of Oslo（奥斯陆大学罗瑟兰太阳物理学中心）
We report multi-wavelength study of a complex M-class solar eruptive flare that consists of three different sets of flare ribbons, viz. circular, parallel, and remote ribbons. Magnetic field modeling of source active region NOAA 12242 exhibits the presence of 3D null-point magnetic topology which encompasses an inner bipolar region. The event initiates with the faint signatures of the circular ribbon along with remote brightening right from the pre-flare phase which points toward the ongoing slow yet persistent null-point reconnection. We first detected flux cancellation and an associated brig…
Dual Origins of Rapid Flare Ribbon Downflows in an X9-class Solar Flare
University of Colorado Boulder（科罗拉多大学博尔德分校）；Southwest Research Institute（西南研究所）；National Solar Observatory（国家太阳观测台）；Royal Observatory of Belgium（比利时皇家天文台）
We present the analysis of three kinds of oscillating behavior using multi-wavelength observations of the 10 November 2013 (SOL2013-11-10T05:14) circular-ribbon flare. This event is a typical circular-ribbon flare with an outer spine structure and homologous jets. We found three kinds of oscillations (or perturbations): i) flux oscillation (or QPP) with a dominant period of about 20 seconds in X-ray, EUV, and microwave emissions, ii) periodic jets with an intermittent cadence of around 72 seconds, iii) an outer loop perturbing half a cycle with a duration of about 168 seconds. Similar to the p…
We studied a circular-ribbon flare, SOL2014-12-17T04:51, with emphasis on its thermal evolution as determined by the Differential Emission Measure (DEM) inversion analysis of the extreme ultraviolet (EUV) images of the Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO). Both temperature and emission measure start to rise much earlier than the flare, along with an eruption and formation of a hot halo over the fan structure. In the main flare phase, another set of ribbons forms inside the circular ribbon, and expands as expected for ribbons at the footpoin…
This paper studies the magnetic topology of successively erupting active regions (ARs) 11429 and 12371. Employing vector magnetic field observations from Helioseismic and Magnetic Imager, the pre-eruptive magnetic structure is reconstructed by a model of non-linear force-free field (NLFFF). For all the five CMEs from these ARs, the pre-eruptive magnetic structure identifies an inverse-S sigmoid consistent with the coronal plasma tracers in EUV observations. In all the eruption cases, the quasi-separatrix layers (QSLs) of Large Q values are continuously enclosing core field bipolar regions in w…
Study of Two Successive Three-Ribbon Solar Flares on 2012 July 6
这封信报告了2012年7月6日在NOAA AR 11515中观察到的两个罕见的三带耀斑（M1.9和C9.2），我们用新太阳望远镜的0.1”分辨率的Halpha观测和Hinode的CaII H图像发现了这两个耀斑。耀斑网站的特点是一个有趣的“鱼骨状”的形态证明了这两个Halpha图像和非线性无力场（NLFFF）外推，其中两个半平行行的低洼，剪切环连接一个细长的，寄生的负场与寄生的正场。NLFFF模型还表明，这两排环的高度是不对称的，有相反的扭曲，并被大规模的磁力线，包括开放的领域。两次耀斑在半小时内相继发生，位于耀斑区的两端。每个耀斑的三个带状物平行于PIL，外部两个位于正磁场中，中心一个位于负磁场中。这两个耀斑都显示出明显朝向偏远地区的Halpha浪涌流，而C9.2耀斑也伴随着EUV喷流，可能沿着开放场线。有趣的是，C9.2耀斑的12-25 keV硬X射线源首先与中央带状物对齐，然后转移到集中在环的较高分支的顶部。这些结果进行了讨论有利于重联沿日冕零线产生的三个耀斑带和相关的喷射。
Solar flare ribbons structured by uncombed chromospheric loops
Max-Planck-Institut für Sonnensystemforschung（马克斯·普朗克太阳系统研究所）；University of St Andrews（圣安德鲁斯大学）；Instituto de Astrofísica de Andalucía, CSIC（安达卢西亚天体物理研究所，西班牙国家研究委员会）；Universitat de Valencia（瓦伦西亚大学）；Instituto Nacional de Técnica Aeroespacial (INTA)（国家航空航天技术研究所）
Solar flares with a fan-spine magnetic topology can form circular ribbons. The previous study based on Hαline observations of the solar flares during March 05, 2014 by Xu et al. (2017) revealed uniform and continuous rotation of the magnetic fan-spine. Preliminary analysis of the flare time profiles revealed quasi-periodic pulsations (QPPs) with similar properties in hard X-rays, Hα, and microwaves. In this work, we address which process the observed periodicities are related to: periodic acceleration of electrons or plasma heating? QPPs are analysed in the Hαemission from the centre of the fa…
In this study, we investigated the energy partition of four confined circular-ribbon flares (CRFs) near the solar disk center, which are observed simultaneously by SDO, GOES, and RHESSI. We calculated different energy components, including the radiative outputs in 1$-$8, 1$-$70, and 70$-$370 Å, total radiative loss, peak thermal energy derived from GOES and RHESSI, nonthermal energy in flare-accelerated electrons, and magnetic free energy before flares. It is found that the energy components increase systematically with the flare class, indicating that more energies are involved in larger flar…
