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1.
R. Chandra B. Schmieder C. H. Mandrini P. Démoulin E. Pariat T. Török W. Uddin 《Solar physics》2011,269(1):83-104
We present and interpret observations of two morphologically homologous flares that occurred in active region (AR) NOAA 10501
on 20 November 2003. Both flares displayed four homologous Hα ribbons and were both accompanied by coronal mass ejections
(CMEs). The central flare ribbons were located at the site of an emerging bipole in the centre of the active region. The negative
polarity of this bipole fragmented in two main pieces, one rotating around the positive polarity by ≈ 110° within 32 hours.
We model the coronal magnetic field and compute its topology, using as boundary condition the magnetogram closest in time
to each flare. In particular, we calculate the location of quasi-separatrix layers (QSLs) in order to understand the connectivity between the flare ribbons. Though several polarities were present in AR 10501,
the global magnetic field topology corresponds to a quadrupolar magnetic field distribution without magnetic null points.
For both flares, the photospheric traces of QSLs are similar and match well the locations of the four Hα ribbons. This globally
unchanged topology and the continuous shearing by the rotating bipole are two key factors responsible for the flare homology.
However, our analyses also indicate that different magnetic connectivity domains of the quadrupolar configuration become unstable
during each flare, so that magnetic reconnection proceeds differently in both events. 相似文献
2.
We present detailed observations of the formations of four distinct coronal dimmings during a flare of 17 September 2002,
which was followed by an eruption of a huge coronal loop system, and then an over-and-out partial halo coronal mass ejection
(CME), with the same direction as the loop system eruption but laterally far offset from the flare site. Among the four dimmings,
two compact ones were symmetrically located in the opposite polarity regions immediately adjacent to the highly sheared magnetic
polarity inversion line in the flare region, and hence were probably composed of bipolar double dimmings due to a flux-rope
eruption and represented its evacuated footpoints. However, another nearby compact dimming and a remote diffuse one were formed
in the opposite polarity footpoint regions of the eruptive loop system, and thus probably consisted of a pair of dimmings
magnetically linked by the erupting loop system and also indicated its evacuated footpoints. The loop system might have played
a role in guiding the erupting flare field and producing the over-and-out CME, but its eruption might simply have been pushed
out by the erupting flare field, because there was no reconnection signature between them. From comparison with a derived
potential-field source-surface (PFSS) magnetic configuration, our observations consistently suggest that the dimmings were
formed in pairs and originated from the eruptions of the two different magnetic systems. We thus define them as “quadrupolar
dimmings.” 相似文献
3.
The structure of the interplanetary magnetic field within the flare streams as well as associated variations of the geomagnetic disturbancy are considered. It is shown that in the main body of the flare stream the magnetic field is determined by the configuration of the large scale magnetic field on the Sun at the flare region. Within the head part of the flare stream the magnetic field represents by itself the compressed field of the background solar wind and hence is determined by the distribution of the super large scale solar magnetic field outside the flare region.A certain asymmetry in the parameters of the magnetic field within the streams associated with geoeffective and non-effective flares is shown to exist. 相似文献
4.
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
5.
C. H. Mandrini P. Demoulin B. Schmieder E. E. Deluca E. Pariat W. Uddin 《Solar physics》2006,238(2):293-312
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
6.
Pankaj Kumar Ablishek K. Srivastava B. Filippov R. Erdélyi Wahab Uddin 《Solar physics》2011,272(2):301-317
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
7.
Peter Foukal 《Solar physics》1970,13(2):330-347
The one-day development of a young bright region with loops (BRL) led to the 1N flare of 00:35 UT, 25 April, 1968.The development of the active region is followed over the two previous rotations, and the peculiar polarity of the BRL, in which neither polarity is clearly leading, is explained from its location on the boundary of two large older active regions. It is likely that the flare occurred as a result of the relaxation of the unusual polarity in the BRL.The prominent active region filament is shown to have formed from the connection of two filaments previously existing in the older AR's.From the lack of meter wave radio emission it is concluded that a very closed field configuration exists in the AR. This is supported by observation of surges contained by the magnetic field, traveling at between 110 and 190 km sec–1.The X-ray emission measure is derived and suggests that the X-ray emission volume is considerably smaller than that emitting H.Comparison of the microwave and X-ray temperatures poses the problem of why the thermal free-free emission in microwaves is so weak from such a strong thermal bremsstrahlung X-ray source. 相似文献
8.
In this paper, we study multiwavelength observations of an M6.4 flare in Active Region NOAA 11045 on 7 February 2010. The space- and ground-based observations from STEREO, SoHO/MDI, EIT, and Nobeyama Radioheliograph were used for the study. This active region rapidly appeared at the north-eastern limb with an unusual emergence of a magnetic field. We find a unique observational signature of the magnetic field configuration at the flare site. Our observations show a change from dipolar to quadrapolar topology. This change in the magnetic field configuration results in its complexity and a build-up of the flare energy. We did not find any signature of magnetic flux cancellation during this process. We interpret the change in the magnetic field configuration as a consequence of the flux emergence and photospheric flows that have opposite vortices around the pair of opposite polarity spots. The negative-polarity spot rotating counterclockwise breaks the positive-polarity spot into two parts. The STEREO-A 195 Å and STEREO-B 171 Å coronal images during the flare reveal that a twisted flux tube expands and erupts resulting in a coronal mass ejection (CME). The formation of co-spatial bipolar radio contours at the same location also reveals the ongoing reconnection process above the flare site and thus the acceleration of non-thermal particles. The reconnection may also be responsible for the detachment of a ring-shaped twisted flux tube that further causes a CME eruption with a maximum speed of 446 km/s in the outer corona. 相似文献
9.
The active region NOAA 8032 of April 15, 1997 was observed to evolve rapidly. The GOES X-ray data showed a number of sub-flares
and two C-class flares during the 8–9 hours of its evolution. The magnetic evolution of this region is studied
to ascertain its role in flare production. Large changes were observed in magnetic field configuration due to the emergence
of new magnetic flux regions (EFR). Most of the new emergence occured very close to the existing magnetic regions, which resulted
in strong magnetic field gradients in this region. EFR driven reconnection of the field lines and subsequent flux cancellation
might be the reason for the continuous occurrence of sub-flares and other related activities. 相似文献
10.
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
11.
We study the magnetic field evolution and topology of the active region NOAA 10486 before the 3B/X1.2 flare of October 26, 2003, using observational data from the French–Italian THEMIS telescope, the Michelson Doppler Imager (MDI) onboard Solar and Heliospheric Observatory (SOHO), the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observation Station (HSOS), and the Transition Region and Coronal Explorer (TRACE). Three dimensional (3D) extrapolation of photospheric magnetic field, assuming a potential field configuration, reveals the existence of two magnetic null points in the corona above the active region. We look at their role in the triggering of the main flare, by using the bright patches observed in TRACE 1600 Å images as tracers at the solar surface of energy release associated with magnetic reconnection at the null points. All the bright patches observed before the flare correspond to the low-altitude null point. They have no direct relationship with the X1.2 flare because the related separatrix is located far from the eruptive site. No bright patch corresponds to the high-altitude null point before the flare. We conclude that eruptions can be triggered without pre-eruptive coronal null point reconnection, and the presence of null points is not a sufficient condition for the occurrence of flares. We propose that this eruptive flare results from the loss of equilibrium due to persistent flux emergence, continuous photospheric motion and strong shear along the magnetic neutral line. The opening of the coronal field lines above the active region should be a byproduct of the large 3B/X1.2 flare rather than its trigger. 相似文献
12.
A recurrent H surge was observed on 7 October, 1991 on the western solar limb with the Meudon MSDP spectrograph. The GOES satellite recorded X-ray subflares coincident with all three events. During two of the surges high-resolutionYohkoh Soft X-ray Telescope (SXT) images have been taken. Low X-ray loops overlying the active region where the surges occurred were continuously restructuring. A flare loop appeared at the onset of each surge event and somewhat separated from the footpoint of the surge. The loops are interpreted as causally related to the surges. It is suggested that surges are due to magnetic reconnection between a twisted cool loop and open field lines. Cold plasma bubbles or jets squeezed among untwisting magnetic field lines could correspond to the surge material. No detection was made of either X-ray emission along the path of the surges or X-ray jets, possibly because of the finite detection threshold of theYohkoh SXT. 相似文献
13.
Using high-cadence magnetograms from the SOHO/MDI we have investigated variations of the photospheric magnetic field during
solar flares and CMEs. In the case of a strong X-class flare of May 2, 1998, we have detected variations of magnetic field
in a form of a rapidly propagating magnetic wave. During the impulsive phase of the flare we have observed a sudden decrease
of the magnetic energy in the flare region. This provides direct evidence of magnetic energy release in solar flares. We discuss
the physics of the magnetic field variations, and their relations to the Moreton Hα waves and the coronal waves observed by
the EIT. 相似文献
14.
Relationship between the geoefficiency of the solar flares as well as of the active regions passing the central meridian of the Sun and the configuration of the large scale solar magnetic field is studied.It is shown that if the tangential component of the large scale magnetic field at the active region or at the flare region is directed southwards, that region and that flare produce geomagnetic storm. In case when the tangential magnetic field is directed northward, the active region and the flares occurring at that region do not cause any geomagnetic disturbance.An index of the geoefficiency of the solar flares and of the active regions is proposed. 相似文献
15.
Wahab Uddin Ramesh Chandra Syed Salman Ali 《Journal of Astrophysics and Astronomy》2006,27(2-3):267-276
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
16.
We analyze large-scale H-alpha movies of the large spot group of Sept. 13–26, 1963, together with radio, ionospheric and magnetic field data as well as white light pictures. The evolution of the group and associated magnetic fields is followed, and the positions of solar flares relative to the fields are noted, along with their morphology. Although the magnetic field is deformed in time, characteristic field structures may be traced through the deformation as the seat of recurrent homologous flares.We find that most flares are homologous, and some are triggered by disturbances elsewhere in the region. We note events produced by surges falling back to the surface, and one flare initiated by a bright bead seen to fly across the region. In almost every case of an isolated type III radio burst, a corresponding H-alpha brightening could be found, but not all flares produced bursts. Flares close to the sunspots are most likely to produce radio bursts. Flare surface waves in the region all travel out to the west, because of more open magnetic field structure there. In one case (Sept. 25) a wave is turned back by the closed field structure to the east.In almost all cases the time association of radio or ionospheric events is with the beginning of the flare or with the flash phase.Several morphological classes of flares are noted as recurrent types. 相似文献
17.
Haimin Wang 《Solar physics》1992,140(1):85-98
This paper studies the evolution of vector magnetic fields in the active region Boulder No. 6233 during an 11-hour observing period and its relationship to an X-3 flare on August 27, 1990.We observed the evolution of magnetic fields, which includes magnetic shear build-up, directly in high-resolution vector magnetograph movies. The magnetic shear is observed to be built up in two ways: (1) shear motion between two poles of opposite magnetic polarities and (2) direct collision of two poles of opposite polarities. When two magnetic elements of opposite polarities are canceling, the field lines are observed to turn from direct connection (potential) to a sheared configuration during the process.An X-3 flare occurred at 2100 UT. The vector magnetic structure showed an unexpected pattern of changes during and after the flare. The shear (defined as the angle between the measured transverse field and the calculated potential field) in the area covering two major footpoints increased rapidly coinciding with the burst of GOES X-ray flux. While the flare faded away in about one hour, the high shear status dropped slowly for the remainder of the observing period. Immediately after the flare, new flux emerged more rapidly and the flow speed of several magnetic elements increased near the flare footpoints.In this active region and a few other flare-productive regions we have studied recently, we always find rapid and complicated flow motions near the sites where flares occur. Photospheric flows appear to be another important factor for the production of flares. 相似文献
18.
NOAA active region 6659, during its June 1991 transit across the solar disk, showed highly sheared vector magnetic field structures
and produced numerous powerful flares, including five white-light flares. Photospheric vector magnetograms of this active
region were obtained at the Huairou Solar Observing Station of the Beijing Astronomical Observatory. After the resolution
of the 180° ambiguity of the transverse magnetic field and transformation of off-center vector magnetograms to the heliographic
plane, we have determined the photospheric vertical current density and discussed the relationship with powerful flares. The
following results were obtained: (a) The powerful 3B/X12 flare on June 9, 1991 was triggered by the interaction between the
large-scale electric current system and magnetic flux of opposite polarity. (b) The kernels of the powerful Hβ flare (sites of the white-light flare) were close to the peaks of the vertical electric current density. (c) Some small-scale
structures of the vertical current relative to the magnetic islands of opposite polarity have not been found. This probably
implies that the electric current is not always parallel to the magnetic field in solar active regions. 相似文献
19.
We study the changes of the CaI λ6102.7 Å line profile and the magnetic field structure during the 1B/M2.2 while-light flare of August 12, 1981. The two brightest flare knots located in the penumbra of a sunspot with a δ configuration are investigated. The 1 ± V line profiles are analyzed. The reduction and analysis of our observations have yielded the following results. (1) The line profiles changed significantly during the flare, especially at the time of optical continuum emission observed near the flare maximum. In addition to the significant decrease in the depth, a narrow polarized emission whose Zeeman splitting corresponded to a longitudinal magnetic field strength of 3600 Gs was observed. This is much larger than the magnetic field strength in the underlying sunspot determined from the Zeeman splitting of absorption lines. (2) The largest changes of the CaI λ6102.7 Å line profile observed during the flare can lead to an underestimation of the longitudinal magnetic field strength measured with a video magnetograph by a factor of 4.5, but they cannot be responsible for the polarity reversal. (3) A sharp short-term displacement of the neutral line occurred at a time close to the flare maximum, which gave rise to a reversed-polarity magnetic field on a small area of the active region, i.e., a magnetic transient. This can be interpreted as a change in the inclination of the magnetic field lines to the line of sight during the flare. The short-term depolarization of the CaI λ6102.7 Å line emission observed at the other flare knot can also be the result of a change in the magnetic field structure. (4) These fast dynamic changes of the magnetic field lines occurred after the maximum of the impulsive flare phase and were close in time to the appearance of type II radio emission. 相似文献
20.
We analyze in detail the X2.6 flare that occurred on 2005 January 15 in the NOAA AR 10720 using multiwavelength observations. There are several interesting properties of the flare that reveal possible two-stage magnetic reconnection similar to that in the physical picture of tether-cutting, where the magnetic fields of two separate loop systems reconnect at the flare core region, and subsequently a large flux rope forms, erupts, and breaks open the overlying arcade fields. The observed manifestations include: (1) remote Hα brightenings appear minutes before the main phase of the flare; (2) separation of the flare ribbons has a slow and a fast phase, and the flare hard X-ray emission appears in the later fast phase; (3) rapid transverse field enhancement near the magnetic polarity inversion line (PIL) is found to be associated with the flare. We conclude that the flare occurrence fits the tether-cutting reconnection picture in a special way, in which there are three flare ribbons outlining the sigmoid configuration. We also discuss this event in the context of what was predicted by Hudson et al. (2008), where the Lorentz force near the flaring PIL drops after the flare and consequently the magnetic field lines there turn to be more horizontal as we observed. 相似文献