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1.
A major two-ribbon X17 flare occurred on 28 October 2003, starting at 11:01 UT in active region NOAA 10486. This flare was accompanied by the eruption of a filament and by one of the fastest halo coronal mass ejections registered during the October–November 2003 strong activity period. We focus on the analysis of magnetic field (SOHO/MDI), chromospheric (NainiTal observatory and TRACE), and coronal (TRACE) data obtained before and during the 28 October event. By combining our data analysis with a model of the coronal magnetic field, we concentrate on the study of two events starting before the main flare. One of these events, evident in TRACE images around one hour prior to the main flare, involves a localized magnetic reconnection process associated with the presence of a coronal magnetic null point. This event extends as long as the major flare and we conclude that it is independent from it. A second event, visible in Hα and TRACE images, simultaneous with the previous one, involves a large-scale quadrupolar reconnection process that contributes to decrease the magnetic field tension in the overlaying field configuration; this allows the filament to erupt in a way similar to that proposed by the breakout model, but with magnetic reconnection occurring at Quasi-Separatrix Layers (QSLs) rather than at a magnetic null point. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.  相似文献   

2.
By means of Hα, EUV, soft X-ray, hard X-ray, and photospheric magnetic field observations, we report the surge-like eruption of a small-scale filament, called “blowout surge” according to recent observations, occurring on a plage region around AR 10876 on 1 May 2006. Along magnetic polarity reversal boundaries with obvious magnetic cancelations, the filament was located underneath a compact coronal arcade and close to one end of large coronal loops around the AR’s periphery. The filament started to erupt about 8 min before the main impulsive phase of a small two-ribbon flare, which had two Hα blue-wing kernels connected by hard X-ray loop-top sources on the both sides of the filament. After the flare end, the filament further underwent a distant eruption following a path nearly along the preexisting large loops, and thus looked like an Hα surge and an EUV jet. During the eruption, a small coronal dimming was formed near the flare, while weak brightenings appeared around the remote end of the large loops. We interpret these joint observations as the filament eruption being confined and guided by the large loops. The filament eruption, initially embedded in one footpoint region of the large loops, can break away from the magnetic restraint of the overlying compact arcade, but might be still limited inside the large loops. As a result, the eruption took a surge form that can only expand laterally along the large loops rather than erupt radially.  相似文献   

3.
Every two-ribbon flare observed during the Skylab period produced an observable coronal transient, provided the flare occurred close enough to the limb. The model presented here treats these two events as a combined process. Transients that occur without flares are believed to involve magnetic fields that are too weak to produce significant chromospheric emission. Adopting the hypothesis that the rising flare loop systems observed during two-ribbon flares are exhibiting magnetic reconnection, a model of a coronal transient is proposed which incorporates this reconnection process as the driving force. When two oppositely directed field lines reconnect a lower loop is created rooted to the solar surface (the flare loop) and an upper disconnected loop is produced which is free to rise. The magnetic flux of these upper loops is proposed as the driver for the transient. The force is produced by the increase in magnetic pressure under the filament and transient.A quantitative model is developed which treats the transient configuration in terms of four distinct parts- the transient itself with its magnetic field and material, the region just below the transient but above the filament, the filament with its magnetic field, and the reconnected flux beneath the filament. Two cases are considered - one in which all the prominence material rises with the transient and one in which the material is allowed to fall out of the transient. The rate of rise of the neutral line during the reconnection process is taken from the observations of the rising X-ray flare loop system during the 29 July, 1973 flare. The MHD equations for the system are reduced to four non-linear ordinary coupled differential equations which are solved using parameters believed to be realistic for solar conditions. The calculated velocity profiles, widths, etc., agree quite well with the observed properties of coronal transients as seen in white light. Since major flares are usually associated with a filament eruption about 10–15 min before the flare and since this model associates the transient with the filament eruption, we suspect that the transient is actually initiated some time before the actual flare itself.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

4.
We observed 4B/X17.2 flare in Hα from super-active region NOAA 10486 at ARIES, Nainital. This is one of the largest flares of current solar cycle 23, which occurred near the Sun’s center and produced extremely energetic emission almost at all wavelengths from γ-ray to radio-waves. The flare is associated with a bright/fast full-halo earth directed CME, strong type II, type III and type IV radio bursts, an intense proton event and GLE. This flare is well observed by SOHO, RHESSI and TRACE. Our Hα observations show the stretching/de-twisting and eruption of helically twisted S shaped (sigmoid) filament in the south-west direction of the active region with bright shock front followed by rapid increase in intensity and area of the gigantic flare. The flare shows almost similar evolution in Hα, EUV and UV. We measure the speed of Hα ribbon separation and the mean value is ∼ 70 km s-1. This is used together with photospheric magnetic field to infer a magnetic reconnection rate at three HXR sources at the flare maximum. In this paper, we also discuss the energetics of active region filament, flare and associated CME.  相似文献   

5.
Using data from the Transition Region and Coronal Explorer (TRACE), Solar and Heliospheric Observatory (SOHO), Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and Hida Observatory (HO), we present a detailed study of an EUV jet and the associated Hα filament eruption in a major flare in the active region NOAA 10044 on 29 July 2002. In the Hα line wings, a small filament was found to erupt out from the magnetic neutral line of the active region during the flare. Two bright EUV loops were observed rising and expanding with the filament eruption, and both hot and cool EUV plasma ejections were observed to form the EUV jet. The two thermal components spatially separated from each other and lasted for about 25 minutes. In the white-light corona data, a narrow coronal mass ejection (CME) was found to respond to this EUV jet. We cannot find obvious emerging flux in the photosphere accounting for the filament eruption and the EUV jet. However, significant sunspot decay and magnetic-flux cancelation owing to collision of opposite flux before the events were noticed. Based on the hard X-ray data from RHESSI, which showed evidence of magnetic reconnection along the main magnetic neutral line, we think that all of the observed dynamical phenomena, including the EUV jet, filament eruption, flare, and CME, should have a close relation to the flux cancelation in the low atmosphere.  相似文献   

6.
Contarino  L.  Romano  P.  Yurchyshyn  V.B.  Zuccarello  F. 《Solar physics》2003,216(1-2):173-188
We describe a filament destabilization which occurred on 5 May 2001 in NOAA AR 9445, before a flare event. The analysis is based on Hα data acquired by THEMIS operating in IPM mode, Hα data and magnetograms obtained at the Big Bear Solar Observatory, MDI magnetograms and 171 Å images taken by TRACE. Observations at 171 Å show that ～ 2.5 hours before the flare peak, the western part of the EUV filament channel seems to split into two parts. The bifurcation of the filament in the Hα line is observed to take place ～ 1.5 hours before the flare peak, while one thread of the filament erupts ～10 min before the peak of the flare. Our analysis of longitudinal magnetograms shows the presence of a knot of positive flux inside a region of negative polarity, which coincides with the site of filament bifurcation. We interpret this event as occurring in two steps: the first step, characterized by the appearance of a new magnetic feature and the successive reconnection in the lower atmosphere between its field lines and the field lines of the old arcade sustaining the filament, leads to a new filament channel and to the observed filament bifurcation; the second step, characterized by the eruption of part of the filament lying on the old PIL, leads to a second reconnection, occurring higher in the corona.  相似文献   

7.
1 INTRODUCTIONCoronal majss ejections (CMEs) are often seen as spectacular eruptions of matter fromthe Sun which propagate outward through the heliosphere and often interact with the Earth'smagnetosphere (Hundhausen, 1997; Gosling, 1997; and references herein). It is well known thatthese interactions can have substalltial consequences on the geomagnetic environment of theEarth, sometimes resulting in damage to satellites (e.g., McAllister et al., 1996; Berdichevskyet al., 1998). CMEs…  相似文献   

8.
1 INTRODUCTION Filaments are cool, dense material suspended in the hot, tenuous corona. It is widely accepted that the global magnetic field surrounding the filaments plays a key role in their formation, structure and stability (Tandberg-Hanssen1995). Fil…  相似文献   

9.
We report observations of the formation of two filaments?–?one active and one quiescent, and their subsequent interactions prior to eruption. The active region filament appeared on 17 May 2007, followed by the quiescent filament about 24 hours later. In the 26 hour interval preceding the eruption, which occurred at around 12:50 UT on 19 May 2007, we see the two filaments attempting to merge and filament material is repeatedly heated suggesting magnetic reconnection. The filament structure is observed to become increasingly dynamic preceding the eruption with two small hard X-ray sources seen close to the active part of the filament at around 01:38 UT on 19 May 2007 during one of the activity episodes. The final eruption on 19 May at about 12:51 UT involves a complex CME structure, a flare and a coronal wave. A magnetic cloud is observed near Earth by the STEREO-B and WIND spacecraft about 2.7 days later. Here we describe the behaviour of the two filaments in the period prior to the eruption and assess the nature of their dynamic interactions.  相似文献   

10.
We present a multi-wavelength analysis of an eruption event that occurred in active region NOAA 11093 on 7 August 2010, using data obtained from SDO, STEREO, RHESSI, and the GONG Hα network telescope. From these observations, we inferred that an upward slow rising motion of an inverse S-shaped filament lying along the polarity inversion line resulted in a CME subsequent to a two-ribbon flare. Interaction of overlying field lines across the filament with the side-lobe field lines, associated EUV brightening, and flux emergence/cancelation around the filament were the observational signatures of the processes leading to its destabilization and the onset of eruption. Moreover, the time profile of the rising motion of the filament/flux rope corresponded well with flare characteristics, viz., the reconnection rate and hard X-ray emission profiles. The flux rope was accelerated to the maximum velocity as a CME at the peak phase of the flare, followed by deceleration to an average velocity of 590 km s−1. We suggest that the observed emergence/cancelation of magnetic fluxes near the filament caused it to rise, resulting in the tethers to cut and reconnection to take place beneath the filament; in agreement with the tether-cutting model. The corresponding increase/decrease in positive/negative photospheric fluxes found in the post-peak phase of the eruption provides unambiguous evidence of reconnection as a consequence of tether cutting.  相似文献   

11.
A theory of two-ribbon solar flares is presented which identifies the primary energy release site with the tops of the flare loops. The flare loops are formed by magnetic reconnection of a locally opened field configuration produced by the eruption of a pre-flare filament. Such eruptions are commonly observed about 15 min prior to the flare itself. It is proposed that the flare loops represent the primary energy release site even during the earliest phase of the flare, i.e., the flare loops are in fact the flare itself.Based upon the supposition that the energy release at the loop tops is in the form of Joulean dissipation of magnetic energy at the rising reconnection site, a quantitative model of the energy release process is developed based upon an analytic reconnecting magnetic field geometry believed to represent the basic process. Predicted curves of energy density vs time are compared with X-ray observations taken aboard Skylab for the events of 29 July, 13 August, and 21 August in 1973. Considering the crudity of the model, the comparisons appear reasonable. The predicted field strengths necessary to produce the observed energy density curves are also reasonable, being in the range 100–1000 G.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

12.
We present the first evidence for occurrences of magnetic interactions between a jet, a filament and coronal loops during a complex event, in which two flares sequen-tially occurred at different positions of the same active region and were closely associated with two successive coronal mass ejections (CMEs), respectively. The coronal loops were located outside but nearby the filament channel before the flares. The jet, originating from the first flare during its rise phase, not only hit the filament body but also met one of the ends of the loops. The filament then underwent an inclined eruption followed by the second flare and met the same loop end once more. Both the jet and the filament erup- tion were accompanied by the development of loop disturbances and the appearances of brightenings around the meeting site. In particular, the erupting filament showed clear manifestations of interactions with the loops. After a short holdup, only its portion passed through this site, while the other portion remained at the same place. Following the fila-ment eruption and the loop disappearance, four dimmings were formed and located near their four ends. This is a situation that we define as "quadrupolar dimmings." It appears that the two flares consisted of a sympathetic pair physically linked by the interaction between the jet and the filament, and their sympathy indicated that of the two CMEs.Moreover, it is very likely that the two sympathetic CMEs were simultaneously associ-ated with the disappearing loops and the quadrupole dimmings.  相似文献   

13.
The solar X-ray observing satellite Yohkoh has discovered various new dynamic features in solar flares and corona, e.g., cusp-shaped flare loops, above-the-loop-top hard X-ray sources, X-ray plasmoid ejections from impulsive flares, transient brightenings (spatially resolved microflares), X-ray jets, large scale arcade formation associated with filament eruption or coronal mass ejections, and so on. It has soon become clear that many of these features are closely related to magnetic reconnection. We can now say that Yohkoh established (at least phenomenologically) the magnetic reconnection model of flares. In this paper, we review various evidence of magnetic reconnection in solar flares and corona, and present unified model of flares on the basis of these new Yohkoh observations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

14.
We carried out a multi-wavelength study of a Coronal Mass Ejection (CME) and an associated flare, occurring on 12 May 1997. We present a detailed investigation of magnetic-field variations in NOAA Active Region 8038 which was observed on the Sun during 7??C?16 May 1997. This region was quiet and decaying and produced only a very small flare activity during its disk passage. However, on 12 May 1997 it produced a CME and associated medium-size 1B/C1.3 flare. Detailed analyses of H?? filtergrams and SOHO/MDI magnetograms revealed continual but discrete surge activity, and emergence and cancellation of flux in this active region. The movie of these magnetograms revealed the two important results that the major opposite polarities of pre-existing region as well as in the emerging-flux region were approaching towards each other and moving magnetic features (MMF) were ejected from the major north polarity at a quasi-periodicity of about ten hours during 10??C?13 May 1997. These activities were probably caused by magnetic reconnection in the lower atmosphere driven by photospheric convergence motions, which were evident in magnetograms. The quantitative measurements of magnetic-field variations such as magnetic flux, gradient, and sunspot rotation revealed that in this active region, free energy was slowly being stored in the corona. Slow low-layer magnetic reconnection may be responsible for the storage of magnetic free energy in the corona and the formation of a sigmoidal core field or a flux rope leading to the eventual eruption. The occurrence of EUV brightenings in the sigmoidal core field prior to the rise of a flux rope suggests that the eruption was triggered by the inner tether-cutting reconnection, but not the external breakout reconnection. An impulsive acceleration, revealed from fast separation of the H?? ribbons of the first 150 seconds, suggests that the CME accelerated in the inner corona, which is also consistent with the temporal profile of the reconnection electric field. Based on observations and analysis we propose a qualitative model, and we conclude that the mass ejections, filament eruption, CME, and subsequent flare were connected with one another and should be regarded within the framework of a solar eruption.  相似文献   

15.
From observations of two-ribbon solar flares, we present a new line of evidence that magnetic reconnection is of key importance in magnetospheric substorms. We infer that in substorms reconnection of closed field lines in the near-Earth thinned plasma sheet both initiates and is driven by the overall MHD instability that drives the tailward expulsion of the reconnected closed field (0 loops). The general basis for this inference is the longstanding notion that two-ribbon flares and substorms are essentially similar phenomena, driven by similar processes. We give an array of observed similarities that substantiate this view. More specifically, our inference for substorms is drawn from observations of filament eruptions in two-ribbon flares, from which we conclude that the heart of the overall instability consists of reconnection and eruption of the closed magnetic field in and around the filament. We propose that essentially the same overall instability operates in substorms. Our point is not that the magnetic field configuration or the microphysics in substorms is identical to that in two-ribbon flares, but that the overall instability results from essentially the same combination of reconnection and eruption of closed magnetic field.  相似文献   

16.
Observations of the quiescent filament eruption and the spotless two-ribbon flare of 12 September 2000 are presented. A simple flare morphology, large spatial scales, and a suitable viewing angle provide insight into characteristics of the energy release process which is attributed to the reconnection process in the current sheet formed below the eruptive filament. The flare ribbons appeared and started to expand laterally while the filament was still recognizable, enabling simultaneous measurements of the ribbon separation w and the height of the lower edge of the filament, h. The ratio w/h estimated for the expanding portions of ribbons indicates that the width-to-length ratio of the current sheet at the onset of the fast reconnection ranges between and . The ribbon elements characterized by w/h> remained stationary. The Nançay radioheliograph data in the decimeter–meter wavelengths show one group of radio bursts ahead of the filament (moving type IV burst) and another group behind the filament. The centroids of the radio sources behind the filament were confined to the region outlined by the lower edge of the filament and the magnetic inversion line, suggestive of emission from the current sheet. Sources were preferably located close to the lower edge of the filament and some appeared close to the magnetic inversion line. Two possible explanations are discussed: one in terms of the fast-mode bow shocks in the reconnection outflow jets, and another in terms of a multiple tearing of the current sheet and subsequent coalescence of plasmoids.  相似文献   

17.
Radosław Rek 《Solar physics》2010,267(2):361-375
Solar flares take place in regions of strong magnetic fields and are generally accepted to be the result of a resistive instability leading to magnetic reconnection. When new flux emerges into a pre-existing active region it can act as a flare and coronal mass ejection trigger. In this study we observed active region 10955 after the emergence of small-scale additional flux at the magnetic inversion line. We found that flaring began when additional positive flux levels exceeded 1.38×1020 Mx (maxwell), approximately 7 h after the initial flux emergence. We focussed on the pre-flare activity of one B-class flare that occurred on the following day. The earliest indication of activity was a rise in the non-thermal velocity one hour before the flare. 40 min before flaring began, brightenings and pre-flare flows were observed along two loop systems in the corona, involving the new flux and the pre-existing active region loops. We discuss the possibility that reconnection between the new flux and pre-existing loops before the flare drives the flows by either generating slow mode magnetoacoustic waves or a pressure gradient between the newly reconnected loops. The subsequent B-class flare originated from fast reconnection of the same loop systems as the pre-flare flows.  相似文献   

18.
We present a theory of filament eruption before the impulsive phase of solar flares. We show that the upward motion of the magnetic X-point tracing the filament eruption begins several minutes before the impulsive phase of the flare, where the explosive magnetic reconnection starts at the X-point magnetic field configuration located under the filament. No change occurs in the character of the motion of the X-point during the onset of the explosive magnetic reconnection. The upward speed of the X-point is about 110 km s-1 at the onset of the impulsive phase. We give an important condition leading to filament eruptions, which relate to the state of the current sheet under the filament, where the magnetic energy can be released.  相似文献   

19.
We present and interpret observations of the preflare phase of the eruptive flare of 15 November, 1991 in NOAA AR 6919. New flux emerged in this region, indicated by arch filaments in Hα and increasing vertical flux in vector magnetograms. With increasing frequency before the eruption, transient dark Hα fibrils were observed that crossed Hα bright plage and the magnetic inversion line to extend from the region of flux emergence to the filament, whose eruption was associated with the flare. These crossing fibrils were dynamic, and were often associated with sites of propagating torsional motion. These sites propagated from the region of flux emergence into the filament flux system. We interpret these morphological and dynamic features in terms of relaxation after magnetic reconnection episodes which create longer field lines within the filament flux system, as envisioned in the tether cutting model, and transfer twist to it, as well. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005086108043  相似文献   

20.
Predictions of Energy and Helicity in Four Major Eruptive Solar Flares   总被引：1，自引：0，他引：1  
In order to better understand the solar genesis of interplanetary magnetic clouds (MCs), we model the magnetic and topological properties of four large eruptive solar flares and relate them to observations. We use the three-dimensional Minimum Current Corona model (Longcope, 1996, Solar Phys. 169, 91) and observations of pre-flare photospheric magnetic field and flare ribbons to derive values of reconnected magnetic flux, flare energy, flux rope helicity, and orientation of the flux-rope poloidal field. We compare model predictions of those quantities to flare and MC observations, and within the estimated uncertainties of the methods used find the following: The predicted model reconnection fluxes are equal to or lower than the reconnection fluxes inferred from the observed ribbon motions. Both observed and model reconnection fluxes match the MC poloidal fluxes. The predicted flux-rope helicities match the MC helicities. The predicted free energies lie between the observed energies and the estimated total flare luminosities. The direction of the leading edge of the MC’s poloidal field is aligned with the poloidal field of the flux rope in the AR rather than the global dipole field. These findings compel us to believe that magnetic clouds associated with these four solar flares are formed by low-corona magnetic reconnection during the eruption, rather than eruption of pre-existing structures in the corona or formation in the upper corona with participation of the global magnetic field. We also note that since all four flares occurred in active regions without significant pre-flare flux emergence and cancelation, the energy and helicity that we find are stored by shearing and rotating motions, which are sufficient to account for the observed radiative flare energy and MC helicity.  相似文献   

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