We present new results from the Interface Region Imaging Spectrograph showing the dynamic evolution of chromospheric evaporation and condensation in a flare ribbon, with the highest temporal and spatial resolution to date. IRIS observed the entire impulsive phase of the X-class flare SOL2014-09-10T17:45 using a 9.4 second cadence `sit-and-stare' mode. As the ribbon brightened successively at new positions along the slit, a unique impulsive phase evolution was observed for many tens of individual pixels in both coronal and chromospheric lines. Each activation of a new footpoint displays the same initial coronal up-flows of up to ~300 km/s, and chromospheric downflows up to 40 km/s. Although the coronal flows can be delayed by over 1 minute with respect to those in the chromosphere, the temporal evolution of flows is strikingly similar between all pixels, and consistent with predictions from hydrodynamic flare models. Given the large sample of independent footpoints, we conclude that each flaring pixel can be considered a prototypical, `elementary' flare kernel.
We analyze a confined multiple-ribbon M2.1 flare (SOL2015-01-29T11:42) that originated from a fan-spine coronal magnetic field configuration, within active region NOAA 12268. The observed ribbons form in two steps. First, two primary ribbons form at the main flare site, followed by the formation of secondary ribbons at remote locations. We observe a number of plasma flows at extreme-ultraviolet temperatures during the early phase of the flare (as early as 15 min before the onset) propagating towards the formation site of the secondary ribbons. The secondary ribbon formation is co-temporal with…
A statistical study of the chromospheric ribbon evolution in H$α$ two-ribbon flares is performed. The data set consists of 50 confined ($62\,\%$) and eruptive ($38\,\%$) flares that occurred from June 2000 to June 2015. The flares are selected homogeneously over the H$α$ and $\textit{GOES}$ (Geostationary Operational Environmental Satellite) classes, with an emphasis on including powerful confined flares and weak eruptive flares. H$α$ filtergrams from Kanzelhöhe Observatory in combination with $\textit{MDI}$ (Michelson Doppler Imager) and $\textit{HMI}$ (Helioseismic and Magnetic Imager) magne…
We present an analysis of the apparent elongation motion of flare ribbons along the polarity inversion line (PIL) as well as the shear of flare loops in several two-ribbon flares. Flare ribbons and loops spread along the PIL at a speed ranging from a few to a hundred km/s. The shear measured from conjugate foot-points is consistent with the measurement from flare loops, and both show the decrease of shear toward a potential field as a flare evolves and ribbons and loops spread along the PIL. Flares exhibiting fast bi-directional elongation appear to have a strong shear, which may indicate a la…
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…
We present a database of 3137 solar flare ribbon events corresponding to every flare of GOES class C1.0 and greater within 45 degrees from the central meridian, from April 2010 until April 2016, observed by the \emph{Solar Dynamics Observatory}. For every event in the database, we compare the GOES peak X-ray flux with corresponding active-region and flare-ribbon properties. We find that while the peak X-ray flux is not correlated with the active region unsigned magnetic flux, it is strongly correlated with the flare ribbon reconnection flux, flare ribbon area, and the fraction of active region…
We consider the observational basis for the belief that flare ribbons in the chromosphere result from energy transport from the overlying corona. We study ribbons of small flares using magnetic as well as intensity data from the Hinode, SDO and IRIS missions. While most ribbons appear connected to the corona, and they over-lie regions of significant vertical magnetic field, we examine one ribbon with no clear evidence for such connections. Evolving horizontal magnetic fields seen with Hinode suggest that reconnection with pre-existing fields below the corona can explain the data. The identific…
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…
We study a complex GOES M1.1 circular ribbon flare and related pre-flare activity on 26 January 2015 [SOL26-01-2015] in solar active region NOAA 12268. This flare activity was observed by the AIA on board SDO and the RHESSI. The examination of photospheric magnetograms during the extended period, prior to the event, suggests the successive development of a so-called 'anemone' type magnetic configuration. NLFFF extrapolation reveals a fan-spine magnetic configuration with the presence of a coronal null-point. We found that the pre-flare activity in the active region starts ~15 min prior to the …
Magnetic flux ropes play a key role in triggering solar flares in the solar atmosphere. In this paper, we investigate the evolution of active region NOAA 12268 within 36 hours from 2015 January 29 to 30, during which a flux rope was formed and three M-class and three C-class flares were triggered without coronal mass ejections. During the evolution of the active region, the flare emission seen in the H$α$ and ultraviolet wavebands changed from a circular shape (plus an adjacent conjugated ribbon and a remote ribbon) to three relatively straight and parallel ribbons. Based on a series of recons…
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…
A second peak in extreme ultraviolet sometimes appears during the gradual phase of solar flares, which is known as EUV late phase (ELP). Stereotypically ELP is associated with two separated sets of flaring loops with distinct sizes, and it has been debated whether ELP is caused by additional heating or extended plasma cooling in the longer loop system. Here we carry out a survey of 55 M-and-above GOES-class flares with ELP during 2010--2014. Based on the flare-ribbon morphology, these flares are categorized as circular-ribbon (19 events), two-ribbon (23 events), and complex-ribbon (13 events) …
We report flare ribbons approach (FRA) during a multiple-ribbon M-class flare on 2015 November 4 in NOAA AR 12443, obtained by the Interface Region Imaging Spectrograph and the Solar Dynamics Observatory. The flare consisted of a pair of main ribbons and two pairs of secondary ribbons. The two pairs of secondary ribbons were formed later than the appearance of main ribbons, with respective time delays of 15 and 19 minutes. The negative-polarity main ribbon spread outward faster than the first secondary ribbon with the same polarity in front of it, and thus the FRA was generated. Just before th…
The photospheric response to solar flares, also known as coronal back reaction, is often observed as sudden flare-induced changes in vector magnetic field and sunspot motions. However, it remains obscure whether evolving flare ribbons, the flare signature closest to the photosphere, are accompanied by changes in vector magnetic field therein. Here we explore the relationship between the dynamics of flare ribbons in the chromosphere and variations of magnetic fields in the underlying photosphere, using high-resolution off-band H-alpha images and near-infrared vector magnetograms of the M6.5 fla…
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…
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…
A solar jet on 2014 July 31, which was accompanied by a GOES C1.3 flare and a mini-filament eruption at the jet base, was studied by using observations taken by the New Vacuum Solar Telescope and the Solar Dynamic Observatory. Magnetic field extrapolation revealed that the jet was confined in a fan-spine magnetic system that hosts a null point at the height of about 9 Mm from the solar surface. An inner flare ribbon surrounded by an outer circular ribbon and a remote ribbon were observed to be associated with the eruption, in which the inner and remote ribbons respectively located at the footp…
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…
We analyze a unique event with an M1.8 confined circular-ribbon flare on 2016 February 13, with successive formations of two circular ribbons at the same location. The flare had two distinct phases of UV and EUV emissions with an interval of about 270 s, of which the second peak was energetically more important. The first episode was accompanied by the eruption of a mini-filament and the fast elongation motion of a thin circular ribbon (CR1) along the counterclockwise direction at a speed of about 220 km/s. Two elongated spine-related ribbons were also observed, with the inner ribbon co-tempor…
Flare ribbons are bright manifestations of flare energy dissipation in the lower solar atmosphere. For the first time, we report on high-resolution imaging spectroscopy observations of flare ribbons situated off-limb in the H$β$ and Ca II 8542 Å lines and make a detailed comparison with radiative hydrodynamic simulations. Observations of the X8.2-class solar flare SOL2017-09-10T16:06 UT obtained with the Swedish Solar Telescope reveal bright horizontal emission layers in H$β$ line wing images located near the footpoints of the flare loops. The apparent separation between the ribbon observed in…
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 provide an important clue to the magnetic reconnection process and associated magnetic field topology in the solar corona. We detected a large-scale secondary flare ribbon of a circular shape that developed in association with two successive M-class flares and one CME. The ribbon revealed interesting properties such as 1) a quasi-circular shape and enclosing the central active region; 2) the size as large as 500\arcsec\, by 650\arcsec\,, 3) successive brightenings in the clockwise direction at a speed of \kms{160} starting from the nearest position to the flaring sunspots, …
We present temporal variations of the Si IV line profiles at the flare ribbons in three solar flares observed by the Interface Region Imaging Spectrograph (IRIS). In the M1.1 flare on 2014 September 6 and the X1.6 flare on 2014 September 10, the Si IV line profiles evolve from wholly redshifted to red-wing enhanced with the flare development. However, in the B1.8 flare on 2016 December 2, the Si IV line profiles are wholly redshifted throughout the flare evolution. We fit the wholly redshifted line profiles with a single Gaussian function but the red-asymmetric ones with a double Gaussian func…
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$-$8, 1$-$70, and 70$-$370 Å, total radiative loss, peak thermal energy derived from GOES and RHESSI, nonthermal energy in flare-accelerated electrons, and magnetic free energy before flares. It is found that the energy components increase systematically with the flare class, indicating that more energies are involved in larger flar…
In this paper, we present unique observations of a blowout coronal jet that possibly triggered a two-ribbon confined C1.2 flare in a bipolar solar active region NOAA 12615 on 2016 December 5. The jet activity initiates at chromospheric/transition-region heights with a small brightening that eventually grows in a larger volume with well developed standard morphological jet features, viz., base and spire. The spire widens up with a collimated eruption of cool and hot plasma components, observed in the 304 and 94 A channels of AIA, respectively. The speed of the plasma ejection, which forms the j…
Employing the high spatio-temporal Interface Region Imaging Spectrograph 1330 Å observations, we investigated the jet-like features that occurred during the X8.2 class flare in NOAA active region (AR) 12673 on 2017 September 10. These jet-like features were rooted in the flare ribbons. We examined 15 features, and the mean values of the lifetimes, projected widths, lengths and velocities of these features were 87 s, 890 km, 2.7 Mm and 70 km s$^{-1}$, respectively. We also observed many jet-like features which happened during the X1.0 class flare on 2014 October 25. We studied the spectra at th…
On 23 July 2016 after 05:00\,UTC, the first 48-antenna stage of the Siberian Radioheliograph detected two flares of M7.6 and M5.5 GOES importance that occurred within half an hour in the same active region. Their multi-instrument analysis reveals the following. The microwave spectra were flattened at low frequencies and the spectrum of the stronger burst had a lower turnover frequency. Each flare was eruptive, emitted hard X-rays and gamma-rays exceeding 800\,keV, and had a rare three-ribbon configuration. An extended hard X-ray source associated with a longest middle ribbon was observed in th…
On the 2012 October 23 circular ribbon flare: emission features and magnetic topology
环带耀斑通常与含有零点的脊扇型磁拓扑有关。本文利用\textit{Solar Dynamics Observatory}、\textit{Hinode}和\textit{Ramaty High Energy Solar Spectroscopic Imager}的多波长观测资料，对2012年10月23日发生的X级环带耀斑进行了研究。在\ion{Ca}{2} H辐射中，耀斑呈现出三条带状，其中两条带状的高度拉长的带状物分别位于准圆形带状物的内侧和外侧。在极紫外（EUV）辐射中显示出一个热通道，推断出磁通量绳的存在。两个12- 25 keV能带的硬X射线源位于该热通道的足点。利用非线性无力磁场外推法，我们确定了三种拓扑结构：（1）一个三维零点，（2）在零点扇形下方的磁通绳，（3）由活动区的类四极磁场诱导的大尺度准分界线层（QSL）。我们发现，零点是嵌入在大规模的QSL。在我们的例子中，必须考虑所有三个确定的拓扑结构来解释与观测到的耀斑相关的所有发射特征。此外，HXR源被认为是磁绳内部或边界附近重联的结果。
