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1.
Series of white light heliograms and oft- and on-band H filtergrams have been obtained, with an average spatial resolution of 1, to study the flare active McMath region 15403 on 11 July, 1978. A great number of accurate heliographic positions were determined for the umbrae, the white light flare patches and several bright H flare knots, as well as along the principal zero filament and an arch prominence. Using the measured heliographic coordinates of these objects their motions could be analyzed in some detail. The velocities of several different objects could be deduced from the coordinates. Since the heliocentric angle of the region was about 45°, the variation in apparent heliographic coordinates also enabled some variations in heights to be determined.It is pointed out that the flare when fully developed, consisted almost entirely of loops. The zero filament which was activated prior to the flare ran between two umbrae of common penumbra and opposite polarity, one belonging to an old, the other to a new spot group. The white light flare developed on both sides of the filament where it passed between these two umbrae; it was also the place where the flare started. Observational evidence appears to indicate that the erupted filament re-formed from below.An indication has been found that there was a link between the motion of some umbrae and the major flare occurrence. 相似文献
2.
Katsuo Tanaka 《Solar physics》1976,47(1):247-259
We show observational results on the pre-flare evolutions of H structures as well as the developments of H flares. It is shown that the chromospheric features are brought to a sheared state before flares due to motions of footpoints which correspond to particular sunspot motions. Generally in evolutions of the chromospheric features it is found that motions and reconnections of the footpoints play essential roles. The following three stages are found for development of the neutral line filament before flares: (1) formation of a filament as a result of reconnection; (2) increase of the shear of the filament due to the shear motion; and (3) reconnection of fine components of the filament to form an elongated component immediately before flares. We further show developments of two particular flares with and without the filament, and point out basic release processes of flares. The flare that occurred at the filament (July 5, 1974) started with the activation of the elongated component of the filament after the process (3). The main phase of a two-ribbon flare is considered as the rises of short components of the filament triggered by the rising motion of the elongated component. The flare of September 10, 1974 occurred at the region where fibrils connect the sunspots in distorted form. Pre-flare distortion was produced by translational rotation of the sunspot. Development of this two-ribbon flare is interpreted as being due to successive rises of the fibrils with a self-trigger mechanism.On leave from Tokyo Astronomical Observatory (present address). 相似文献
3.
We have analyzed the variations in shear angle over a time interval of 30 s during a flare on June 11, 1991, using Kodaikanal Observatory spectroheliogram and photoheliogram data, and assuming H filaments are a proxy for the neutral lines. The changes in shear angles have been analysed at two points of the filament. The orientation of the H filament underwent a considerable change of 55° from June 10, 1991 to prior to the start of the flare on June 11, 1991. The photoheliogram on June 10, 1991 shows considerable twisting of the umbrae (in one common penumbra) and broke into parts before the onset of the flare on June 11, 1991. The twisting of umbrae on June 10, 1991 shows that sunspot proper motion plays an important role in bringing a non-potential character to the field lines. This in turn develops shear and kink and it is argued that changes in filament orientation over a small interval of a half minute triggers the eruption of the flare. 相似文献
4.
We have evaluated the shear angle of the neutral line of the non-potential magnetic field for one or two days prior to and after the flare event for 10 cases. We have used the H filament positions to evaluate the shear in the neutral line. We find from the samples we have studied that it is the change in the shear that occurs a day prior to the flare that can lead to the event. This change can be in either direction, i.e., it can be a large increase from a small value or a decrease from a large initial value. Thus it is the change in the shear angle that seems to be a deciding criterion for a flare to occur and not a large value for the shear angle itself. We have one instance where there was no significant change in the shear angle over a period of a few days and this region, although similar to other active regions studied, did not produce any flare activity. 相似文献
5.
We analyze the changes that projection effects produce in the evaluation of magnetic shear in off-disk center active regions by comparing angular shear calculated in image plane and heliographic coordinates. We describe the procedure for properly evaluating magnetic shear by transforming the observed vector magnetic field into the heliographic system and then apply this procedure to evaluate magnetic shear along the magnetic neutral line in an active region that was observed on 1984 April 24 at a longitude offset of -45°. In particular, we show that the number of critically sheared pixels along an east-west directed segment of the neutral line in the leader sunspot group changes from 16 in the image plane magnetogram to 14 in the heliographic magnetogram. We also show that the critical shear as calculated in the image plane served as a good predictor for the location of flaring activity since the flare ribbons of the great flare of April 24 bracketed the inversion line where the critical shear was located. These results indicate that for this particular region, projection effects did not significantly affect the evaluation of critical shear. 相似文献
6.
M. J. Hagyard 《Solar physics》1988,115(1):107-124
We have analyzed the vector magnetic field of an active region at a location of repeated flaring to determine the nature of the currents flowing in the areas where the flares initiated. The component of electric current density crossing the photosphere along the line-of-sight was derived from the observed transverse component of the magnetic field. The maximum concentrations of these currents occurred exactly at the sites of flare initiation and where the photospheric field was sheared the most. The calculated distribution of current density at the flare sites suggested that currents were flowing out of an area of positive magnetic polarity and across the magnetic inversion line into two areas of negative polarity. This interpretation was reinforced by a calculation of the source field, the magnetic field produced in the photosphere by the electric currents above the photosphere. In the vicinity of the flare sites, the calculated source field exhibited three particular characteristics: (1) maximum magnitudes at the sites of flare initiation, (2) a rotational direction where the vertical current density was concentrated, and (3) a fairly constant angular orientation with the magnetic inversion line. The source field was thus very similar to the field produced by two arcades of currents crossing the inversion line at the locations of greatest magnetic shear with orientations of about 60° to the inversion line. With this orientation, the inferred arcades would be aligned with the observed chromospheric fibrils seen in the H data so that the currents were field-aligned above the photosphere. The field thus exhibited a vertical gradient of magnetic shear with the shear decreasing upward from the photosphere. We estimated the currents in the two arcades by matching the source field derived from observations with that produced by a model of parallel loops of currents. We found that the loops of the model would each have a radius of 4500 km, a separation of 1830 km, and carry a current of 0.15 × 1012 A. Values of vertical current densities and source fields appearing in the umbrae of the two large sunspots away from the flare sites were shown to lie at or below the level of uncertainty in the data. The main source of this uncertainty lay in the method by which the 180° ambiguity in the azimuth of the transverse field is resolved in umbral areas. We thus concluded that these quantities in large umbrae should be treated with a healthy skepticism. Finally, we found that the source field at the flare sites was produced almost entirely by the angular difference between the observed and potential field and not by the difference in field intensity. 相似文献
7.
K. Jockers 《Solar physics》1976,47(1):221-221
The two-dimensional force-free field equations are studied. The solar photosphere is considered as flat and infinitely extended and the magnetic field component perpendicular to the photosphere is prescribed as the field of a submerged line dipole, i.e. with two magnetic polarities divided by a straight infinitely long neutral line. In addition the shear of the field lines along the neutral line, i.e. the difference of the coordinate parallel to the neutral line of the two foot-points of a field line, is prescribed as a function f of the distance to the neutral line times a nonnegative constant . The function f is zero at the neutral line, goes through a maximum and drops to zero at large distances from the neutral line. The case = 0 corresponds to the current-free field. An approximate solution is obtained by a test function method. It is shown that for certain choices of the function f there exists a maximum value of beyond which a steady continuation of the solution is impossible. This forces the field to jump to a state of lower energy. The potential field, for instance, is such a lower energy state. Since the shear was prescribed as a boundary condition, the jump of the magnetic field will always be accompanied by a field line reconnection. Even though the field calculated does not closely resemble the flare geometry it is speculated that discontinuities like this one may also occur in more realistic field configurations and may actually trigger the flare.An extended version of this paper is to be published elsewhere. 相似文献
8.
Of 21 flares of importance 1 or greater, observed on 15 days, all were found to lie adjacent to a neutral line in the longitudinal component of photospheric magnetic fields. In most of these cases, the flare consisted of two or more segments separated by the neutral line and located in areas of strong field and high-longitudinal field gradient. In some cases, the flare segments extended into areas of weak-magnetic field and low-field gradient, but maintained an orientation adjacent to a neutral line.Optical and magnetic field records of higher resolution were obtained on 6 July 1965. These observations reveal an excellent correlation between the size, shape, and intensity of the H fine structures and the longitudinal component of the photospheric magnetic fields, except in the vicinity of the neutral line. Sections of the neutral line are marked by long fibrils lying perpendicular to the neutral line or by small filaments lying along the neutral line.The development of a flare of importance 1 in this region appeared to be more precisely related to the neutral line than was found for the flares and magnetic fields observed with lower resolution. The two major segments of this flare lengthened in directions approximately parallel to the neutral line, while simultaneously drifting perpendicularly away from the neutral line. The initial rate of drift systematically varied from 1 to 12 km/sec at a series of positions approximately parallel to the neutral line and corresponding to increasing distance from strong fields. The rate of drift was also observed to decelerate throughout the life of the flare. 相似文献
9.
On September 14–18, 2000, a medium-small solar active region was observed at Ganyu Station of Purple Mountain Observatory. Its spots were not large, but it had a peculiar active filament. On Sep.16, a flare of importance IIIb with rather intense geophysical effects was produced. Our computation of the magnetic structure of the active region reveals that the rope-shaped filament was concerned with a low magnetic arc close to magnetic neutral line. An intense shear of magnetic field occurred near magnetic rope. The QSL analysis shows that a 3-D magnetic reconnection might appear in the vicinity of filament, and this can be used to interpret the formation of a large flare. 相似文献
10.
We have analyzed the H filtergrams and vector magnetograms of the active region NOAA 7070, in which a 3B/X3.3 flare occurred on February 27, 1992. The average area per sunspot of this active region was in declining phase at the time of the flare. The vector magnetograms indicate that the magnetic field was non-potential at the flaring site. Besides non-potentiality, the longitudinal field gradient was found to be the highest at the region showing initial H brightening. Further, in H filtergrams no appreciable change in the morphology of the filament tracing the magnetic neutral line was noticed in the post-flare stage. Also, the photospheric vector magnetograms show considerable shear in post-flare magnetic field of the active region. In this paper we present the observations and discuss the possible mechanism responsible for the 3B/X3.3 flare. 相似文献
11.
This paper is based on observations in the H line with the aim to carry out a detailed study of the spotless flare of importance 1N that was observed at the Baikal Astrophysical Observatory on 16 March 1981. The study focuses on the evolution of the region of interest from the time of its appearance from behind the limb, and on the pre-flare activation of chromospheric features four hours before the flare. The disturbances that preceded the flare spanned an area of about 120 square degrees. The bulk of activations occurred along and near the path of the polarity inversion line (PIL) of the longitudinal component of the magnetic field. The flare was preceded by an eruptive filament, a disturbance of the fine structure of supergranulation cells, and by the formation of dark vortex structures in regions where flare ribbons form; dark mottles in these regions signaled the operation of an oscillatory process with a period of about 3–4 min, and the region where one of the flare ribbons formed showed a `tunnel' of a system of small-scale dark loops. A close association of the chromospheric activations and flare mottles, with the boundaries of the chromospheric and magnetic networks, is established. 相似文献
12.
Vector magnetic field evolution,energy storage,and associated photospheric velocity shear within a flare-productive active region 总被引：1，自引：0，他引：1
The evolution of vector photospheric magnetic fields has been studied in concert with photospheric spot motions for a flare-productive active region. Over a three-day period (5–7 April, 1980), sheared photospheric velocity fields inferred from spot motions are compared both with changes in the orientation of transverse magnetic fields and with the flare history of the region. Rapid spot motions and high inferred velocity shear coincide with increased field alignment along the B
L= 0 line and with increased flare activity; a later decrease in velocity shear precedes a more relaxed magnetic configuration and decrease in flare activity. Crude energy estimates show that magnetic reconfiguration produced by the relative velocities of the spots could cause storage of 1032 erg day–1, while the flares occurring during this time expended 1031 erg day–1.Maps of vertical current density suggest that parallel (as contrasted with antiparallel) currents flow along the stressed magnetic loops. For the active region, a constant-, force-free magnetic field (J = B) at the photosphere is ruled out by the observations.Presently located at NASA/MSFC, Huntsville, Ala. 35812, U.S.A. 相似文献
13.
1986年2月4日太阳耀斑的演化研究 总被引：1，自引：0，他引：1
本文根据乌鲁木齐天文站的H_α耀斑及3.2cm射电流量观侧资料、云南天文台的黑子精细结构照相和Marshall Space Flight Center的向量磁场图,对1986年2月4日的六个耀斑的形态相关及演化联系,特别是0736UT 4B/3X大耀斑的发展过程进行了综合分析。主要结果是: 1.4日大耀斑的初始亮点和闪光相的主要形态演化,与活动区中沿中性线新浮现的强大电流/磁环系密切相关。后者的主要标志是沿中性线的长的剪切半影纤维及它两端的偶极旋涡黑子群(1_3F_3)。 2.上述大耀斑与1972年8月4日0624 UT大耀斑爆发的磁场背景及主要形态特征相似,表明两者的储能和触发机制可能相同。 3.大耀斑爆发的H_α初始亮点,双带出现,环系形成,亮物质抛射和吸收冕珥等现象同3.2cm射电流量的变化在时间上有较好的对应关系。 4.重复性的前期小耀斑爆发位置和发展趋势与大耀斑的主要形态及演化特征相似。它们相对于剪切的纵场中性线两侧的位置相近或相同。因而,可以看作上述强大电流/磁环系不稳性发展过程中的前置小爆发。 相似文献
14.
In this paper, the chromospheric magnetic structures and their relation to the photospheric vector magnetic field in the vicinity of a dark filament in active region 5669 have been demonstrated. Structural variations are shown in chromospheric magnetograms after a solar flare. Filament-like structures in the chromospheric magnetograms occurred after a solar flare. They correspond to the reformation of the chromospheric dark filament, but there is no obvious variation of the photospheric magnetic field. We conclude that (a) some of the obvious changes of the chromospheric magnetic fields occurred after the flare, and (b) a part of these changes is perhaps due to flare brightening in the chromospheric H line.During the reforming process of the dark filament, a part of its chromospheric velocity field shows downward flow, and it later shows upward flow. 相似文献
15.
A quantitative study relating observed shear in photospheric magnetic fields to repeated flaring 总被引：3，自引：0，他引：3
In this paper we present a quantitative evaluation of the shear in the magnetic field along the neutral line in an active region during an epoch of flare activity. We define shear as the angular difference in the photosphere between the potential magnetic field, which fits the boundary conditions imposed by the observed line-of-sight field, and the observed magnetic field. For the active region studied, this angular difference (shear) is non-uniform along the neutral line with maxima occurring at the locations of repeated flare onsets. We suggest that continued magnetic evolution causes the field's maximum shear to exceed a critical value of shear, resulting in a flare around the site of maximum shear. Evidently, the field at the site of the flare must relax to a state of shear somewhat below the critical value (but still far from potential), with subsequent evolution returning the field to the critical threshold. We draw this inference because several flares occurred at sites of maximum photospheric shear which were persistent in location.NOAA, Boulder, Colorado. 相似文献
16.
Tuan-Hui Zhou Hai-Sheng Ji 《中国天文和天体物理学报》2009,9(3)
We give an extensive multi-wavelength analysis of an eruptive M1.0/1N class solar flare, which occurred in the active region NOAA 10044 on 2002 July 26. Our empha-sis is on the relationship between magnetic shear and flare shear. Flare shear is defined as the angle formed between the line connecting the centroids of the two ribbons of the flare and the line perpendicular to the magnetic neutral line. The magnetic shear is computed from vector magnetograms observed at Big Bear Solar Observatory (BBSO), while the flare shear is computed from Transition Region and Coronal Explorer (TRACE) 1700A images. By a detailed comparison, we find that: 1) The magnetic shear and the flare shear of this event are basically consistent, as judged from the directions of the transverse mag-netic field and the line connecting the two ribbons' centroids. 2) During the period of the enhancement of magnetic shear, flare shear had a fast increase followed by a fluctuated decrease. 3) When the magnetic shear stopped its enhancement, the fluctuated decreasing behavior of the flare shear became very smooth. 4) Hard X-ray (HXR) spikes are well correlated with the unshearing peaks on the time profile of the rate of change of the flare shear. We give a discussion of the above phenomena. 相似文献
17.
By using a topological model for the potential magnetic field above the photosphere, the appearance and development of the separator as a result of vortex plasma flows in the locality of the photospheric neutral line is considered. The possible relation of such vortex flows with a flare activity is revealed. The arrangement and shape of the flare ribbons in the chromosphere, the formation of X-ray intersecting loops, the early appearance of bright knots on flare ribbon edges are naturally explained by the model provided a reconnecting current sheet arises along the separator in the coronal magnetic field of active regions as a result of the evolution of the magnetic field sources in the photosphere. 相似文献
18.
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
19.
《Chinese Astronomy and Astrophysics》1982,6(3):186-192
An analysis of 20 flares of spotless regions observed at Yunnan Observatory during the peak years of Cycle 21 shows 1) the fraction of flares produced in spotless regions is about 3%, 2) their Carrington longitudes show a tendency to drift eastward, 3) the majority of spotless flares are low-energy flares, 4) the background conditions for producing spotless flares are the same as for flares in general, namely, there must be local magnetic structures of opposite polarities. The spotless flares occur on the sides or in the vicinity of the local neutral line.The quiescent dark filaments floating on the neutral line are activated a few hours and one or two days before the flare, the filament nearest to the flare position first enlarges, accompanied by brightening of plages. A few minutes before the flare, or during the flare, this filament rapidly weakens, even vanishes. Meanwhile, visible fibrils become less inclined to the main filament showing pressure force is transformed into shear force. 相似文献
20.
Frances Tang 《Solar physics》1978,60(1):119-122
H flare patches usually do not occur in sunspot umbrae. Presented here are cases of a type of umbral flare in which the flare patch originated in, and was confined to, the p spot umbra. All are H subflares. Two of the four flares were accompanied by type III radio bursts. The simplicity and similarity of the magnetic fields of these regions were striking. 相似文献