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1.
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
2.
We propose a new model for the initiation of solar coronal mass ejections (CMEs) and CME-associated flares. The model is inferred from observations of a quiescent filament eruption in the north-western quadrant of the solar disk on 4 September 2000. The event was observed with the Siberian Solar Radio Telescope (5.7 GHz), the Nobeyama Radioheliograph (17 GHz) and SOHO/EIT and LASCO. Based on the observations, we suggest that the eruption could be caused by the interaction of two dextral filaments. According to our model, these two filaments merge together to form a dual-filament system tending to form a single long filament. This results in a slow upward motion of the dual-filament system. Its upward expansion is prevented by the attachment of the filaments to the photosphere by filament barbs as well as by overlying coronal arcades. The initial upward motion is caused by the backbone magnetic field (first driving factor) which connects the two merging filaments. Its magnetic flux increases slowly due to magnetic reconnection of the cross-interacting legs of these filaments. If a total length of the dual-filament system is large enough, then the filament barbs detach themselves from the solar surface due to magnetic reconnection between the barbs with oppositely directed magnetic fields. The detachment of the filament barbs completes the formation of the eruptive filaments themselves and determines the helicity sign of their magnetic fields. The appearance of a helical magnetic structure creates an additional upward-directed force (second driving factor). A combined action of these two factors causes acceleration of the dual-filament system. If the lifting force of the two factors is sufficient to substantially extend the overlying coronal magnetic arcade, then magnetic reconnection starts below the eruptive filament in accordance with the classical scheme, and the third driving factor comes into play. 相似文献
3.
We present multiwavelength observations of a large-amplitude oscillation of a polar-crown filament on 15 October 2002, which
has been reported by Isobe and Tripathi (Astron. Astrophys.
449, L17, 2006). The oscillation occurred during the slow rise (≈1 km s−1) of the filament. It completed three cycles before sudden acceleration and eruption. The oscillation and following eruption
were clearly seen in observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). The oscillation was seen only in a part of the filament, and it appears to be a standing oscillation rather than
a propagating wave. The amplitudes of velocity and spatial displacement of the oscillation in the plane of the sky were about
5 km s−1 and 15 000 km, respectively. The period of oscillation was about two hours and did not change significantly during the oscillation.
The oscillation was also observed in Hα by the Flare Monitoring Telescope at the Hida Observatory. We determine the three-dimensional
motion of the oscillation from the Hα wing images. The maximum line-of-sight velocity was estimated to be a few tens of kilometers
per second, although the uncertainty is large owing to the lack of line-profile information. Furthermore, we also identified
the spatial displacement of the oscillation in 17-GHz microwave images from Nobeyama Radio Heliograph (NoRH). The filament
oscillation seems to be triggered by magnetic reconnection between a filament barb and nearby emerging magnetic flux as was
evident from the MDI magnetogram observations. No flare was observed to be associated with the onset of the oscillation. We
also discuss possible implications of the oscillation as a diagnostic tool for the eruption mechanisms. We suggest that in
the early phase of eruption a part of the filament lost its equilibrium first, while the remaining part was still in an equilibrium
and oscillated. 相似文献
4.
Solar filaments/prominences exhibit rotational motion during different phases of their evolution from their formation to eruption. We have observed the rotational/vortical motion in the photosphere near the ends of ten filaments during their initial phase of eruption, at the onset of the fast rise phase. All the filaments were associated with active regions. The photospheric vortical motions we observed lasted for 4?–?20 minutes. In the vicinity of the conjugate ends of the filament the direction of rotation was opposite, except for two cases, where rotational motion was observed at only one end point. The sudden onset of a large photospheric vortex motion could have played a role in destabilizing the filament by transporting axial flux into the activated filament thereby increasing the outward magnetic pressure in it. The outward magnetic pressure may have pushed the filament/flux rope to the height where the torus instability criterion was satisfied, and hence it could have caused the filament instability and eruption. 相似文献
5.
The resistive MHD equations are numerically solved in two dimensions for an initial-boundary-value problem which simulates reconnection between an emerging magnetic flux region and an overlying coronal magnetic field. The emerging region is modelled by a cylindrical flux tube with a poloidal magnetic field lying in the same plane as the external, coronal field. The plasma betas of the emerging and coronal regions are 1.0 and 0.1, respectively, and the magnetic Reynolds number for the system is 2 × 103. At the beginning of the simulation the tube starts to emerge through the base of the rectangular computational domain, and, when the tube is halfway into the computational domain, its position is held fixed so that no more flux of plasma enters through the base. Because the time-scale of the emergence is slower than the Alfvén time-scale, but faster than the reconnection time-scale, a region of closed loops forms at the base. These loops are gradually opened and reconnected with the overlying, external magnetic field as time proceeds.The evolution of the plasma can be divided into four phases as follows: First, an initial, quasi-steady phase during which most of the emergence is completed. During this phase, reconnection initially occurs at the slow rate predicted by the Sweet model of diffusive reconnection, but increases steadily until the fast rate predicted by the Petschek model of slow-shock reconnection is approached. Second, an impulsive phase with large-scale, super-magnetosonic flows. This phase appears to be triggered when the internal mechanical equilibrium inside the emerging flux tube is upset by reconnection acting on the outer layers of the flux tube. During the impulsive phase most of the flux tube pinches off from the base to form a cylindrical magnetic island, and temporarily the reconnection rate exceeds the steady-state Petschek rate. (At the time of the peak reconnection rate, the diffusion region at the X-line is not fully resolved, and so this may be a numerical artifact.) Third, a second quasi-steady phase during which the magnetic island created in the impulsive phase is slowly dissipated by continuing, but low-level, reconnection. And fourth, a static, non-evolving phase containing a potential, current-free field and virtually no flow.During the short time in the impulsive phase when the reconnection rate exceeds the steady-state Petschek rate, a pile-up of magnetic flux at the neutral line occurs. At the same time the existing Petschek-slow-mode shocks are shed and replaced by new ones; and, for a while, both new and old sets of slow shocks coexist. 相似文献
6.
Jiangtao Su Yu Liu Hiroki Kurokawa Xinjie Mao Shangbin Yang Hongqi Zhang Haimin Wang 《Solar physics》2007,242(1-2):53-63
We present new observations of the interactions of two close, but distinct, Hα filaments and their successive eruptions on
5 November 1998. The magnetic fields of the filaments are both of the sinistral type. The interactions between the two filaments
were initiated mainly by an active filament of one of them. Before the filament eruptions, two dark plasma ejections and chromospheric
brightenings were observed. They indicate that possible magnetic reconnection had occurred between the two filaments. During
the first filament eruption, salient dark mass motions transferring from the left erupting filament into the right one were
observed. The right filament erupted 40 minutes later. This second filament eruption may have been the result of a loss of
stability owing to the sudden mass injection from the left filament. Based on the Hα observations, we have created a sketch
for understanding the interactions between two filaments and accompanying activities. The traditional theory of filament merger
requires that the filaments share the same filament channel and that the reconnection occurs between the two heads, as simulated
by DeVore, Antiochos, and Aulanier (Astrophys. J.
629, 1122, 2005; 646, 1349, 2006). Our interpretation is that the external bodily magnetic reconnection between flux ropes of the same chirality is another
possible way for two filament bodies to coalesce.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
7.
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
8.
Vršnak Bojan Warmuth Alexander Maričić Darije Otruba Wolfgang Ruždjak Vladimir 《Solar physics》2003,217(1):187-198
A huge filament eruption of 12 September 2000 associated with a two-ribbon spotless flare is described. During the acceleration phase the shape of the filament changed, and signatures of topological restructuring of large-scale coronal magnetic fields were inferred by tracking changes of nearby coronal holes. At the same time electron beams associated with the flare impulsive phase escaped into interplanetary space. Based on the time–spatial relationships a hypothesis is put forward, according to which the reconnection between the arcade magnetic field and the ambient field provides a temporary link between the open field lines and the flare energy release site, enabling the escape of electron beams into interplanetary space. 相似文献
9.
Transition-region explosive events (TREEs) have long been proposed as a consequence of magnetic reconnection. However, several
critical issues have not been well addressed, such as the location of the reconnection site, their unusually short lifetime
(about one minute), and the recently discovered repetitive behaviour with a period of three to five minutes. In this paper,
we perform MHD numerical simulations of magnetic reconnection, where the effect of five-minute solar p-mode oscillations is examined. UV emission lines are synthesised on the basis of numerical results in order to compare with
observations directly. It is found that several typical and puzzling features of the TREEs with impulsive bursty behaviour
can only be explained if there exist p-mode oscillations and the reconnection site is located in the upper chromosphere at a height range of around 1900 km < h < 2150 km above the solar surface. Furthermore, the lack of proper motions of the high-velocity ejection may be due to a
rapid change of temperature along the reconnection ejecta. 相似文献
10.
P. C. Liewer E. M. De Jong J. R. Hall R. A. Howard W. T. Thompson J. L. Culhane L. Bone L. van Driel-Gesztelyi 《Solar physics》2009,256(1-2):57-72
A filament eruption, accompanied by a B9.5 flare, coronal dimming, and an EUV wave, was observed by the Solar TERrestrial Relations Observatory (STEREO) on 19 May 2007, beginning at about 13:00 UT. Here, we use observations from the SECCHI/EUVI telescopes and other solar observations to analyze the behavior and geometry of the filament before and during the eruption. At this time, STEREO A and B were separated by about 8.5°, sufficient to determine the three-dimensional structure of the filament using stereoscopy. The filament could be followed in SECCHI/EUVI 304 Å stereoscopic data from about 12 hours before to about 2 hours after the eruption, allowing us to determine the 3D trajectory of the erupting filament. From the 3D reconstructions of the filament and the chromospheric ribbons in the early stage of the eruption, simultaneous heating of both the rising filamentary material and the chromosphere directly below is observed, consistent with an eruption resulting from magnetic reconnection below the filament. Comparisons of the filament during eruption in 304 Å and Hα? show that when it becomes emissive in He II, it tends to disappear in Hα?, indicating that the disappearance probably results from heating or motion, not loss, of filamentary material. 相似文献
11.
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
12.
A filament disappearance event was observed on 22 May 2008 during our recent campaign JOP 178. The filament, situated in the Southern Hemisphere, showed sinistral chirality consistent with the hemispheric rule. The event was well observed by several observatories, in particular by THEMIS. One day, before the disappearance, Hα observations showed up- and down-flows in adjacent locations along the filament, which suggest plasma motions along twisted flux rope. THEMIS and GONG observations show shearing photospheric motions leading to magnetic flux canceling around barbs. STEREO A, B spacecraft with separation angle 52.4°, showed quite different views of this untwisting flux rope in He ii 304 Å images. Here, we reconstruct the three-dimensional geometry of the filament during its eruption phase using STEREO EUV He ii 304 Å images and find that the filament was highly inclined to the solar normal. The He ii 304 Å movies show individual threads, which oscillate and rise to an altitude of about 120 Mm with apparent velocities of about 100 km?s?1 during the rapid evolution phase. Finally, as the flux rope expands into the corona, the filament disappears by becoming optically thin to undetectable levels. No CME was detected by STEREO, only a faint CME was recorded by LASCO at the beginning of the disappearance phase at 02:00 UT, which could be due to partial filament eruption. Further, STEREO Fe xii 195 Å images showed bright loops beneath the filament prior to the disappearance phase, suggesting magnetic reconnection below the flux rope. 相似文献
13.
Jiayan Yang Yunchun Jiang Bo Yang Junchao Hong Dan Yang Yi Bi Ruisheng Zheng Haidong Li 《New Astronomy》2012,17(8):732-738
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
14.
A major solar active event called Bastille Day Event occurred in AR 9077 on July 14, 2000. Simultaneous occurrence of a filament
eruption, a flare and a coronal mass ejection was observed in this event. Previous analyses of this event show that before
the event, there existed an activation and eruption of a huge trans-equatorial filament, which might play a crucial role in
triggering the Bastille Day event. This implies that independent flux systems are closely related to and affect each other,
which has encouraged us to investigate the catastrophic behavior of a multiple coronal flux rope system with the use of a
2.5-D time-dependent MHD model. A force-free field that contains three separate coronal flux ropes is taken to be the initial
state. Starting from this state, we increase either the annular or the axial flux of a certain flux rope to examine the catastrophic
behavior of the system in two regimes, the ideal MHD regime and the resistive MHD regime. It is found that a catastrophe occurs
if the flux exceeds a certain critical value, or the magnetic energy of the system exceeds a certain threshold: the rope of
interest breaks away from the base and escapes to infinity, leaving a current sheet below. Moreover, the destiny of the remainder
flux ropes relies on whether reconnection takes place across the current sheet. In the ideal MHD regime, i.e., in the absence of reconnection, these ropes remain to be attached to the base in equilibrium, whereas in the resistive MHD
regime they abruptly erupt upward during reconnection and escape to infinity. Reconnection causes the field lines to close
back to the base and thus changes the background field outside the attached flux ropes in such a way that the constraint on
these ropes is substantially relaxed and the corresponding catastrophic energy threshold is reduced accordingly, leading to
a catastrophic eruption of these ropes. Since magnetic reconnection is generally inevitable when a current sheet forms and
develops through an eruption of one flux rope, the eruption of this flux rope must lead to an eruption of the others. This
provides an example to demonstrate the interaction between several independent magnetic flux systems in different regions,
as implied by the Bastille Day event, and may serve as a possible mechanism for sympathetic events occurring on the Sun. 相似文献
15.
Haidong Li Jiayan Yang Yunchun Jiang Yi Bi Zhining Qu Hechao Chen 《Astrophysics and Space Science》2018,363(2):26
We present a study of a mini-filament erupting in association with a circular ribbon flare observed by NVST and SDO/AIA on 2014 March 17. The filament was located at one footpoint region of a large loops. The potential field extrapolation shows that it was embedded under a magnetic null point configuration. First, we observed a brightening of the filament at the corresponding EUV images, close to one end of the filament. With time evolution, a circular flare ribbon was observed around the filament at the onset of the eruption, which is regarded as a signature of reconnection at the null point. After the filament activation, its eruption took the form of a surge, which ejected along one end of a large-scale closed coronal loops with a curtain-like shape. We conjecture that the null point reconnection may facilitate the eruption of the filament. 相似文献
16.
Magnetic reconnection in the temperature minimum region of the solar photosphere can account for the canceling magnetic features
on the Sun. Litvinenko (1999a) showed that a reconnection model explains the quiet-Sun features with the magnetic flux cancelation
rate of order 1017 Mx hr−1. In this paper the model is applied to cancelation in solar active regions, which is characterized by a much larger rate
of cancelation ∖ ge1019 Mx hr−1. In particular, the evolution of a photospheric canceling feature observed in an active region on July 2, 1994 is studied.
The theoretical predictions are demonstrated to be in reasonable agreement with the measured speed of approaching magnetic
fragments, the magnetic field in the fragments, and the flux cancelation rate, deduced from the combined Big Bear Hα time-lapse
images and videomagnetograms calibrated against the daily NSO/Kitt Peak magnetogram. Of particular interest is the prediction
that photospheric reconnection should lead to a significant upward mass flux and the formation of a solar filament. Hα observations
indeed showed a filament that had one of its ends spatially superposed with the canceling feature.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005284116353 相似文献
17.
Several laboratory experiments on magnetic field line reconnection are briefly reviewed. Emphasis is placed on the double inverse pinch device (DIPD) in which magnetic flux is built up during a quiescent reconnection phase and then abruptly transferred during an impulsive reconnection phase. Scaling estimates show that this impulsive phase corresponds to a solar release of 1030 ergs in 102 seconds with the production of GeV potentials. The trigger for the impulsive flare is a conduction mode instability (ion-acoustic) which abruptly changes the resistance of the neutral point region when the reconnection current density reaches a critical value.Some results are presented from another reconnection device which has exactly antiparallel fields at the boundaries. This flat plate device develops one x-type neutral point rather than tearing into many neutral points. The reconnection rate is more quiescent than in the DIPD. A mild conduction mode instability occurs. The results suggest that regions with flattened boundary fields may not be as conducive to flares as regions with more curved fields. 相似文献
18.
We studied the evolution of a small eruptive flare (GOES class C1) from its onset phase using multi-wavelength observations
that sample the flare atmosphere from the chromosphere to the corona. The main instruments involved were the Coronal Diagnostic
Spectrometer (CDS) aboard SOHO and facilities at the Dunn Solar Tower of the National Solar Observatory/Sacramento Peak. Transition
Region and Coronal Explorer (TRACE) together with Ramaty High-Energy Spectroscopic Imager (RHESSI) also provided images and
spectra for this flare. Hα and TRACE images display two loop systems that outline the pre-reconnection and post-reconnection magnetic field lines and
their topological changes revealing that we are dealing with an eruptive confined flare. RHESSI data do not record any detectable
emission at energies ≥25 keV, and the observed count spectrum can be well fitted with a thermal plus a non-thermal model of
the photon spectrum. A non-thermal electron flux F ≈ 5 × 1010 erg cm−2 s−1 is determined. The reconstructed images show a very compact source whose peak emission moves along the photospheric magnetic
inversion line during the flare. This is probably related to the motion of the reconnection site, hinting at an arcade of
small loops that brightens successively. The analysis of the chromospheric spectra (Ca II K, He I D3 and Hγ, acquired with a four-second temporal cadence) shows the presence of a downward velocity (between 10 and 20 km s−1) in a small region intersected by the spectrograph slit. The region is included in an area that, at the time of the maximum
X-ray emission, shows upward motions at transition region (TR) and coronal levels. For the He I 58.4 and O v 62.97 lines, we determine a velocity of ≈−40 km s−1 while for the Fe XIX 59.22 line a velocity of ≈−80 km s−1 is determined with a two-component fitting. The observations are discussed in the framework of available hydrodynamic simulations
and they are consistent with the scenario outlined by Fisher (1989). No explosive evaporation is expected for a non-thermal
electron beam of the observed characteristics, and no gentle evaporation is allowed without upward chromospheric motion. It
is suggested that the energy of non-thermal electrons can be dissipated to heat the high-density plasma, where possibly the
reconnection occurs. The consequent conductive flux drives the evaporation process in a regime that we can call sub-explosive. 相似文献
19.
Kazunari Shibata 《Astrophysics and Space Science》1998,264(1-4):129-144
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
20.
E. R. Priest 《Solar physics》1976,47(1):41-75
Current sheets have been suggested as the site for flare energy release because they can convert magnetic energy very rapidly into both heat and directed plasma energy. Also they contain electric fields with the potential of accelerating particles to high energies.The basic properties of current sheets are first reviewed. For instance, magnetic flux may be carried into a current sheet and annihilated. An exact solution for such a process in an infinitely long sheet has been found; it describes the annihilation of fields which are inclined at any angle, not just 180°. Moreover, field lines which are expelled from the ends of a current sheet can be described as having been reconnected. The only workable model for fast reconnection in the solar atmosphere, namely Petschek's mechanism, has recently been put on a firm foundation; it gives a reconnection rate which depends on the electrical conductivity but is typically a tenth or a hundredth of the Alfvén speed. A current sheet may be formed when the sources of an initially potential field start to move; a simple analytic technique for finding the position and shape of such a sheet in two dimensions now exists. Finally, a sheet with no transverse magnetic field component is subject to the tearing-mode instability, which rapidly produces a series of loops in the field.The main ways in which current sheets have been used for solar flare models is described. Syrovatskii's mechanism relies on the increase of the electric current density during the formation of a sheet, to a value in excess of the critical value j
* for the onset of microinstabilities. But Anzer has recently demonstrated that the critical value is most unlikely to be reached during the initial formation process. Sturrock, on the other hand, has advocated the occurrence of the tearing-mode instability in an open streamer-like configuration (which may result from the eruption of a force-free field). But recent observations do not point to that as the relevant configuration. Rather, they suggest that flares are triggered by the emergence of new magnetic flux from below the solar photosphere. This has led Heyvaerts, Priest, and Rust (1976) to propose a new emerging flux model, according to which, as more and more flux emerges, so reconnection occurs, producing some preflare heating. When the current sheet reaches such a height (around the transition region) that its current density exceeds j
*, then the impulsive phase of the flare is triggered. The main phase is caused by an enhanced level of magnetic energy conversion in a turbulent current sheet. The type of flare depends on the magnetic environment in which the emerging flux finds itself. A surge flare results if the flux appears near a strong unipolar region such as a simple sunspot, whereas a two ribbon flare may be produced by flux emergence near an active region filament, in which case the main phase energy is released from the field that surrounds the filament. 相似文献