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1.
Observations of the large two-ribbon flare on 7 November 2004 made using SOHO and TRACE data are interpreted in terms of a three-dimensional magnetic field model. Photospheric flux evolution indicates that ?1.4×1043 Mx2 of magnetic helicity was injected into the active region during the 40-hour buildup prior to the flare. The magnetic model places a lower bound of 8×1031 ergs on the energy stored by this motion. It predicts that 5×1021 Mx of flux would need to be reconnected during the flare to release the stored energy. This total reconnection compares favorably with the flux swept up by the flare ribbons, which we measure using high-time-cadence TRACE images in 1?600 Å. Reconnection in the model must occur in a specific sequence that would produce a twisted flux rope containing significantly less flux and helicity (1021 Mx and ?3×1042 Mx2, respectively) than the active region as a whole. The predicted flux compares favorably with values inferred from the magnetic cloud observed by Wind. This combined analysis yields the first quantitative picture of the flux processed through a two-ribbon flare and coronal mass ejection.  相似文献   

2.
Three homologous coronal mass ejections (CMEs) occurred on 5, 12 and 16 May 1997 from the single magnetic polarity inversion line (PIL) of AR8038. The three events together provide STEREO-like quadrature views of the 12 May 1997 CME and EIT double dimming. The recurrent CMEs with the nearly identical post-CME potential state and the ‘sigmoid to arcade to sigmoid’ transformations indicate a repeatable store?–?release?–?restore process of the free energy. How was the free magnetic energy re-introduced to the potential state corona after each release in this decaying active region? Making use of the known time interval bounded by the adjacent homologous CMEs, we made the following measures. The unsigned magnetic flux of AR8038, ΦAR, decreased by approximately 18% during 66 h, while the unsigned flux, ΦPIL, in a Gaussian-weighted PIL-region containing the flare site increased by about 50% during 36 hrs prior to the C1.3 flare on 12 May 1997. The significant increase of ΦPIL demonstrates the magnetic gradient increase and the build-up of free energy in the PIL-region during the time leading to the eruption. Fourier local correlation tracking (FLCT) flow speed in AR8038 ranges from 0 to 292.8 m?s?1 with a mean value of 63.2 m?s?1. The flow field contains a persistent converging flow towards the flaring PIL and an effective shear flow distributed in the AR. Minor angular motions were found. An integrated proxy Poynting flux S h estimates the energy input to the corona to be on the order of 1.15×1032 erg during the 66 hrs before the C1.3 flare. It suggests that sufficient energy for a flare/CME can be introduced to the corona on the order of several days by the flows deduced from photospheric magnetic field motions in this small decaying active region.  相似文献   

3.
Horizontal proper motions were measured with local correlation tracking (LCT) techniques in active region NOAA 11158 on 2011 February 15 at a time when a major (X2.2) solar flare occurred. The measurements are based on continuum images and magnetograms of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The observed shear flows along the polarity inversion line were rather weak (a few 100 m s–1). The counter‐streaming region shifted toward the north after the flare. A small circular area with flow speeds of up to 1.2 km s–1 appeared after the flare near a region of rapid penumbral decay. The LCT signal in this region was provided by small‐scale photospheric brigthenings, which were associated with fast traveling moving magnetic features. Umbral strengthening and rapid penumbral decay was observed after the flare. Both phenomena were closely tied to kernels of white‐light flare emission. The white‐light flare only lasted for about 15 min and peaked 4 min earlier than the X‐ray flux. In comparison to other major flares, the X2.2 flare in active region NOAA 11158 only produced diminutive photospheric signatures (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
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   

5.
In this study, photospheric vector magnetograms obtained with the Synoptic Optical Long-term Investigations of the Sun (SOLIS) survey are used as boundary conditions to model three-dimensional nonlinear force-free (NLFF) coronal magnetic fields as a sequence of NLFF equilibria in spherical geometry. We study the coronal magnetic field structure inside an active region and its temporal evolution. We compare the magnetic field configuration obtained from NLFF extrapolation before and after the flaring event in active region (AR) 11117 and its surroundings observed on 27 October 2010, and we also compare the magnetic field topologies and the magnetic energy densities and study the connectivities between AR 11117 and its surroundings. During the investigated time period, we estimate the change in free magnetic energy from before to after the flare to be 1.74×1032?erg, which represents about 13.5?% of the NLFF magnetic energy before the flare. In this study, we find that electric currents from AR 11117 to its surroundings were disrupted after the flare.  相似文献   

6.
Yurchyshyn  Vasyl B.  Wang  Haimin 《Solar physics》2001,202(2):309-318
In this paper we study the evolution of magnetic fields of a 1F/2.4C solar flare and following magnetic flux cancellation. The data are Big Bear Solar Observatory and SOHO/MDI observations of active region NOAA 8375. The active region produced a multitude of subflares, many of them being clustered along the moat boundary in the area with mixed polarity magnetic fields. The study indicates a possible connection between the flare and the flux cancellation. The cancellation rate, defined from the data, was found to be 3×1019 Mx h–1. We observed strong upward directed plasma flows at the cancellation site. Suggesting that the cancellation is a result of reconnection process, we also found a reconnection rate of 0.5 km s–1, which is a significant fraction of Alfvén speed. The reconnection rate indicates a regime of fast photospheric reconnection happening during the cancellation.  相似文献   

7.
Energy is stored when the force-free magnetic field in an active region departs from a potential field, the departure showing up as a shear in the field. As soon as the field untwists, energy will be released to produce flares. Based on this idea, we derived an analytical solution of the equation of force-free field under the assumption of a constant force-free factor, and found expressions for seven important quantities for quadrupolar sunspots: the magnetic energy of the twisted field, that of potential field, the extractable free energy ΔM, the magnetic flux, the total current, the force-free factor and the field decay factor, in terms of three observables: the field intensity, the twist angle and the distance between two spots of the same polarity. The expression for ΔM can be useful in solar prediction work. For the active region of August, 1972, we found ΔM up to 6 × 1032 erg, sufficient to supply the energy of the observed flare activity. Observations of this active region are in good general agreement with our theoretical expectations: in the entire twisting of the quadrupolar sunspot group, each spot assumes the form of a complete spiral in the clockwise direction for each of the four spots.  相似文献   

8.
When magnetic flux emerges from beneath the photosphere, it displaces the preexisting field in the corona, and a current sheet generally forms at the boundary between the old and new magnetic domains. Reconnection in the current sheet relaxes this highly stressed configuration to a lower energy state. This scenario is most familiar and most often studied in flares, where the flux transfer is rapid. We present here a study of steady, quiescent flux transfer occurring at a rate three orders of magnitude lower than that in a large flare. In particular, we quantify the reconnection rate and the related energy release that occurred as the new polarity emerged to form NOAA Active Region 11112 (SOL16 October 2010T00:00:00L205C117) within a region of preexisting flux. A bright, low-lying kernel of coronal loops above the emerging polarity, observed with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory and the X-ray Telescope onboard Hinode, originally showed magnetic connectivity only between regions of newly emerged flux when overlaid on magnetograms from the Helioseismic and Magnetic Imager. Over the course of several days, this bright kernel advanced into the preexisting flux. The advancement of an easily visible boundary into the old flux regions allows measuring the rate of reconnection between old and new magnetic domains. We compare the reconnection rate with the inferred heating of the coronal plasma. To our knowledge, this is the first measurement of steady, quiescent heating related to reconnection. We determined that the newly emerged flux reconnects at a fairly steady rate of 0.38×1016 Mx?s?1 over two days, while the radiated power varies between (2?–?8)×1025 erg?s?1 over the same time. We found that as much as 40 % of the total emerged flux at any given time may have reconnected. The total amounts of transferred flux (～?1×1021 Mx) and radiated energy (～?7.2×1030 ergs) are comparable to that of a large M- or small X-class flare, but are stretched out over 45 hours.  相似文献   

9.
Pores can be exploited for the understanding of the interaction between small-scale vertical magnetic field and the surrounding convective motions as well as the transport of mechanical energy into the chromosphere along the magnetic field. For better understanding of the physics of pores, we investigate tiny pores in a new emerging active region (AR11117) that were observed on 26 October 2010 by the Solar Optical Telescope (SOT) on board Hinode and the Fast Imaging Solar Spectrograph (FISS) of the 1.6 meter New Solar Telescope (NST). The pores are compared with nearby small magnetic concentrations (SMCs), which have similar magnetic flux as the pores but do not appear dark. Magnetic flux density and Doppler velocities in the photosphere are estimated by applying the center-of-gravity method to the Hinode/Spectro-Polarimeter data. The line-of-sight motions in the lower chromosphere are determined by applying the bisector method to the wings of the Hα and the Ca?ii 8542 Å line simultaneously taken by the FISS. The coordinated observation reveals that the pores are filled with plasma which moves down slowly and are surrounded by stronger downflow in the photosphere. In the lower chromosphere, we found that the plasma flows upwards inside the pores while the plasma in the SMCs is always moving down. Our inspection of the Ca?ii 8542 Å line from the wing to the core shows that the upflow in the pores slows down with height and turns into downflow in the upper chromosphere while the downflow in the SMCs gains its speed. Our results are in agreement with the numerical studies which suggest that rapid cooling of the interior of the pores drives a strong downflow, which collides with the dense lower layer below and rebounds into an upflow.  相似文献   

10.
We present a multiwavelength analysis of a long-duration, white-light solar flare (M8.9/3B) event that occurred on 04 June 2007 from AR NOAA 10960. The flare was observed by several spaceborne instruments, namely SOHO/MDI, Hinode/SOT, TRACE, and STEREO/SECCHI. The flare was initiated near a small, positive-polarity, satellite sunspot at the center of the active region, surrounded by opposite-polarity field regions. MDI images of the active region show a considerable amount of changes in the small positive-polarity sunspot of δ configuration during the flare event. SOT/G-band (4305 Å) images of the sunspot also suggest the rapid evolution of this positive-polarity sunspot with highly twisted penumbral filaments before the flare event, which were oriented in a counterclockwise direction. It shows the change in orientation, and also the remarkable disappearance of twisted penumbral filaments (≈35?–?40%) and enhancement in umbral area (≈45?–?50%) during the decay phase of the flare. TRACE and SECCHI observations reveal the successive activation of two helically-twisted structures associated with this sunspot, and the corresponding brightening in the chromosphere as observed by the time-sequence of SOT/Ca?ii H line (3968 Å) images. The secondary, helically-twisted structure is found to be associated with the M8.9 flare event. The brightening starts six?–?seven minutes prior to the flare maximum with the appearance of a secondary, helically-twisted structure. The flare intensity maximizes as the secondary, helically-twisted structure moves away from the active region. This twisted flux tube, associated with the flare triggering, did not launch a CME. The location of the flare activity is found to coincide with the activation site of the helically-twisted structures. We conclude that the activation of successive helical twists (especially the second one) in the magnetic-flux tubes/ropes plays a crucial role in the energy build-up process and the triggering of the M-class solar flare without a coronal mass ejection (CME).  相似文献   

11.
Mathew  Shibu K.  Ambastha  Ashok 《Solar physics》2000,197(1):75-84
Active region NOAA 8038 was observed from 10 to 13 May, 1997 using the USO solar video magnetograph. During this period, the active region was mostly inactive, and gave rise to only a single notable flare of 1N/C1.3 class on May 12, 1997/04:45 UT. The flare occurred in a weak field location, but new emerging fluxes were observed prior to the flare onset. Horizontal motions of the network photospheric magnetic fluxes were inferred using USO and SOHO magnetograms, and velocities in the range 300–800 m s–1 were estimated. The initial flare brightening was observed at the flux cancellation site where magnetic field gradients were found to increase. Detailed analyses of flux motions, cancellation and their relation with the flare are presented.  相似文献   

12.
We present the multiwavelength observations of a flux rope that was trying to erupt from NOAA AR 11045 and the associated M-class solar flare on 12 February 2010 using space-based and ground-based observations from TRACE, STEREO, SOHO/MDI, Hinode/XRT, and BBSO. While the flux rope was rising from the active region, an M1.1/2F class flare was triggered near one of its footpoints. We suggest that the flare triggering was due to the reconnection of a rising flux rope with the surrounding low-lying magnetic loops. The flux rope reached a projected height of ≈0.15R ⊙ with a speed of ≈90 km s−1 while the soft X-ray flux enhanced gradually during its rise. The flux rope was suppressed by an overlying field, and the filled plasma moved towards the negative polarity field to the west of its activation site. We found the first observational evidence of the initial suppression of a flux rope due to a remnant filament visible both at chromospheric and coronal temperatures that evolved a couple of days earlier at the same location in the active region. SOHO/MDI magnetograms show the emergence of a bipole ≈12 h prior to the flare initiation. The emerged negative polarity moved towards the flux rope activation site, and flare triggering near the photospheric polarity inversion line (PIL) took place. The motion of the negative polarity region towards the PIL helped in the build-up of magnetic energy at the flare and flux rope activation site. This study provides unique observational evidence of a rising flux rope that failed to erupt due to a remnant filament and overlying magnetic field, as well as associated triggering of an M-class flare.  相似文献   

13.
The aim of this paper is to look at the magnetic helicity structure of an emerging active region and show that both emergence and flaring signatures are consistent with a same sign for magnetic helicity. We present a multiwavelength analysis of an M1.6 flare occurring in the NOAA active region 10365 on 27 May 2003, in which a large new bipole emerges in a decaying active region. The diverging flow pattern and the “tongue” shape of the magnetic field in the photosphere with elongated polarities are highly suggestive of the emergence of a twisted flux tube. The orientation of these tongues indicates the emergence of a flux tube with a right-hand twist (i.e., positive magnetic helicity). The flare signatures in the chromosphere are ribbons observed in Hα by the MSDP spectrograph in the Meudon solar tower and in 1600 Å by TRACE. These ribbons have a J shape and are shifted along the inversion line. The pattern of these ribbons suggests that the flare was triggered by magnetic reconnection at coronal heights below a twisted flux tube of positive helicity, corresponding to that of the observed emergence. It is the first time that such a consistency between the signatures of the emerging flux through the photosphere and flare ribbons has been clearly identified in observations. Another type of ribbons observed during the flare at the periphery of the active region by the MSDP and SOHO/EIT is related to the existence of a null point, which is found high in the corona in a potential field extrapolation. We discuss the interpretation of these secondary brightenings in terms of the “breakout” model and in terms of plasma compression/heating within large-scale separatrices.  相似文献   

14.
The majority of flare activity arises in active regions which contain sunspots, while Coronal Mass Ejection (CME) activity can also originate from decaying active regions and even so-called quiet solar regions which contain a filament. Two classes of CME, namely flare-related CME events and CMEs associated with filament eruption are well reflected in the evolution of active regions. The presence of significant magnetic stresses in the source region is a necessary condition for CME. In young active regions magnetic stresses are increased mainly by twisted magnetic flux emergence and the resulting magnetic footpoint motions. In old, decayed active regions twist can be redistributed through cancellation events. All the CMEs are, nevertheless, caused by loss of equilibrium of the magnetic structure. With observational examples we show that the association of CME, flare and filament eruption depends on the characteristics of the source regions:
  • ?the strength of the magnetic field, the amount of possible free energy storage,
  • ?the small- and large-scale magnetic topology of the source region as well as its evolution (new flux emergence, photospheric motions, cancelling flux), and
  • ?the mass loading of the configuration (effect of gravity). These examples are discussed in the framework of theoretical models.
    •   相似文献   

    15.
    Shocks driven by fast coronal mass ejections (CMEs) are the dominant particle accelerators in large, “gradual” solar energetic particle (SEP) events. In these events, the event-integrated value of the iron-to-oxygen ratio (Fe/O) is typically ～?0.1, at least at energies of a few MeV/nucleon. However, at the start of some gradual events, when intensities are low and growing, initially Fe/O is ～?1. This value is also characteristic of small, “impulsive” SEP events, in which particle acceleration is due to magnetic reconnection. These observations suggested that SEPs in gradual events also include a direct contribution from the flare that accompanied the CME launch. If correct, this interpretation is of critical importance: it indicates a clear path to interplanetary space for particles from the reconnection region beneath the CME. A key issue for the flare origin is “magnetic connectedness”, i.e., proximity of the flare site to the solar footpoint of the observer’s magnetic field line. We present two large gradual events observed in 2001 by Wind at L1 and by Ulysses, when it was located at >?60° heliolatitude and beyond 1.6 AU. In these events, transient Fe/O enhancements at 5?–?10 MeV/nucleon were seen at both spacecraft, even though one or both is not “well-connected” to the flare. These observations demonstrate that an initial Fe/O enhancement cannot be cited as evidence for a direct flare component. Instead, initial Fe/O enhancements are better understood as a transport effect, driven by the different mass-to-charge ratios of Fe and O. We further demonstrate that the time-constant of the roughly exponential decay of the Fe/O ratio scales as R 2, where R is the observer’s radial distance from the Sun. This behavior is consistent with radial diffusion. These observations thus also provide a potential constraint on models in which SEPs reach high heliolatitudes by cross-field diffusion.  相似文献   

    16.
      相似文献   

    17.
    In this paper, we reconstruct the finite energy force-free magnetic field of the active region NOAA 8100 on 4 November 1997 above the photosphere. In particular, the 3-D magnetic field structures before and after a 2B/X2 flare at 05:58 UT in this region are analyzed. The magnetic field lines were extrapolated in close coincidence with the Yohkoh soft X-ray (SXR) loops accordingly. It is found that the active region is composed of an emerging flux loop, a complex loop system with differential magnetic field shear, and large-scale, or open field lines. Similar magnetic connectivity has been obtained for both instants but apparent changes of the twisting situations of the calculated magnetic field lines can be observed that properly align with the corresponding SXR coronal loops. We conclude that this flare was triggered by the interaction of an emerging flux loop and a large loop system with differential magnetic field shear, as well as large-scale, or open field lines. The onset of the flare was at the common footpoints of several interacting magnetic loops and confined near the footpoints of the emerging flux loop. The sheared configuration remained even after the energetic flare, as demonstrated by calculated values of the twist for the loop system, which means that the active region was relaxed to a lower energy state but not completely to the minimum energy state (two days later another X-class flare occurred in this region).  相似文献   

    18.
    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   

    19.
    Sequences of line-of-sight (LOS) magnetograms recorded by the Michelson Doppler Imager are used to quantitatively characterize photospheric magnetic structure and evolution in three active regions that rotated across the Sun??s disk during the Whole Heliosphere Interval (WHI), in an attempt to relate the photospheric magnetic properties of these active regions to flares and coronal mass ejections (CMEs). Several approaches are used in our analysis, on scales ranging from whole active regions, to magnetic features, to supergranular scales, and, finally, to individual pixels. We calculated several parameterizations of magnetic structure and evolution that have previously been associated with flare and CME activity, including total unsigned magnetic flux, magnetic flux near polarity-inversion lines, amount of canceled flux, the ??proxy Poynting flux,?? and helicity flux. To catalog flare events, we used flare lists derived from both GOES and RHESSI observations. By most such measures, AR 10988 should have been the most flare- and CME-productive active region, and AR 10989 the least. Observations, however, were not consistent with this expectation: ARs 10988 and 10989 produced similar numbers of flares, and AR 10989 also produced a few CMEs. These results highlight present limitations of statistics-based flare and CME forecasting tools that rely upon line-of-sight photospheric magnetic data alone.  相似文献   

    20.
    Longcope  D. W.  Silva  A. V. R. 《Solar physics》1998,179(2):349-377
    Observations of the flare on 7 January 1992 are interpreted using a topological model of the magnetic field. The model, developed here, applies a theory of three-dimensional reconnection to the inferred magnetic field configuration for 7 January. In the model field a new bipole ( 1021 Mx) emerges amidst pre-existing active region flux. This emergence gives rise to two current ribbons along the boundaries (separators) separating the distinct, new and old, flux systems. Sudden reconnection across these boundary curves transfers 3 ×1020 Mx of flux from the bipole into the surrounding flux. The model also predicts the simultaneous (sympathetic) flaring of the two current ribbons. This explains the complex two-loop structure noted in previous observations of this flare. We subject the model predictions to comparisons with observations of the flare. The locations of current ribbons in the model correspond closely with those of observed soft X-ray loops. In addition the footpoints and apexes of the ribbons correspond with observed sources of microwave and hard X-ray emission. The magnitude of energy stored by the current ribbons compares favorably to the inferred energy content of accelerated electrons in the flare.  相似文献   

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