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1.
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
2.
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
3.
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
4.
通过对活动区NOAA 6891中三个X级耀斑前后的向量磁场分析 ,研究耀斑发生条件与耀斑发生前后横向磁场和磁剪切变化的关系。我们发现与Hagyard的耀斑发生条件不同的是 ,强的横向磁场和磁剪切不是活动区中耀斑发生的充要条件。我们的结果表明 ,活动区NOAA 6891 1 991年 30日的耀斑发生在横向磁场和磁剪切剧烈下降后。尽管 1 0月 2 7日的耀斑发生后横向磁场和磁剪切变化很大 ,但由于有新磁流浮现 ,造成磁中性线的改变 ,使得横向磁场和磁剪切变化与耀斑发生的联系变得比较复杂。 相似文献
5.
Tetsuya Watanabe Alphonse C. Sterling Hugh S. Hudson Louise K. Harra 《Solar physics》2001,201(1):71-91
We report temperature diagnostics derived from helium-like ions of sulphur for an active region NOAA 7978 obtained with Bragg Crystal Spectrometer (BCS) on board the Yohkoh satellite. For the same region we estimate conductive flux downward to the chromosphere by the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO) satellite. This region appeared as a region of soft X-ray enhancement in May 1996, underwent a period of enhanced activity coinciding with flux emergence between 6 July and 12 July, and then continued to exist in a nearly flareless state for several solar rotations until November 1996. Energy balance of the non-flaring active region is basically consistent with a model of an arcade of coronal loops having an average loop-top temperature of 4×106 K. Energy from flare activity during a period of flux emergence is comparable to the energy requirements of the non-flaring active region. However, the non-flaring energy is roughly constant for the subsequent solar rotations following the birth of the active region even after the flare activity essentially subsided. Energy partition between flare activity and steady active-region heating thus varies significantly over the lifetime of the active region, and active-region emission cannot always be identified with flaring. 相似文献
6.
Complex sunspots in four active regions of April and May 1980, all exhibiting regions of magnetic classification delta, were studied using data from the NASA Marshall Space Flight Center vector magnetograph. The vector magnetic field structure in the vicinity of each delta was determined, and the location of the deltas in each active region was correlated with the locations and types of flare activity for the regions. Two types of delta-configuration were found to exist, active and inactive, as defined by the relationships between magnetic field structure and activity. The active delta exhibited high flare activity, strong horizontal gradients of the longitudinal (line-of-sight) magnetic field component, a strong transverse (perpendicular to line-of-sight) component, and a highly non-potential orientation of the photospheric magnetic field, all indications of a highly sheared magnetic field. The inactive delta, on the other hand, exhibited little or no flare production, weaker horizontal gradients of the longitudinal component, weaker transverse components, and a nearly potential, non-sheared orientation of the magnetic field. We conclude that the presence of such sheared fields is the primary signature by which the active delta may be distinguished, and that it is this shear which produces the flare activity of the active delta.NASA Graduate Student Research Fellow. 相似文献
7.
A three-dimensional coronal magnetic field is reconstructed for the NOAA active region 11158 on 14 February 2011. A GPU-accelerated direct boundary integral equation (DBIE) method is implemented which is approximately 1000 times faster than the original DBIE used on solar non-linear force-free field modeling. Using the SDO/HMI vector magnetogram as the bottom boundary condition, the reconstructed magnetic field lines are compared with the projected EUV loop structures as observed in the front-view (SDO/AIA) and the side-view (STEREO-A/B) images for the first time; they show very good agreement three-dimensionally. A quantitative comparison with some stereoscopically reconstructed coronal loops shows that the average misalignment angles in our model are at the same order as the state-of-the-art results obtained from reconstructed coronal loops. It is found that the observed coronal loop structures can be grouped into a number of closed and open field structures with some central bright coronal loop features around the polarity inversion line. The reconstructed highly sheared magnetic field lines agree very well with the low-lying sigmoidal filament along the polarity inversion line. This central low-lying magnetic field loop system must have played a key role in powering the flare. It should be noted that while a strand-like coronal feature along the polarity inversion line may be related to the filament, one cannot simply interpret all the coronal bright features along the polarity inversion line as manifestation of the filament without any stereoscopic information. 相似文献
8.
M. J. Hagyard 《Solar physics》1987,107(2):239-246
In this paper we investigate the changes that occur in measured magnetic fields when they are transformed into a heliographic coordinate system. To carry out this investigation we took measurements of the vector magnetic field of an active region that was observed at 1/3 the solar radius from disk center and transformed the observed field into heliographic coordinates. We also examined differences in the calculated potential field that occur when the heliographic normal component of the field is used as the boundary condition rather than the observed line-of-sight component. The results of this analysis show (1) that the observed fields of sunspots more closely resemble the generally accepted picture of the distribution of umbral fields if they are displayed in heliographic coordinates, (2) that the differences in the potential calculations are less than 200 G in field strength and 20° in field azimuth outside sunspots, and (3) that differences in the two potential calculations in the sunspot areas are no more than 400 G in field strength but range from 60 to 80° in field azimuth in localized umbral areas. 相似文献
9.
Katsuo Tanaka 《Solar physics》1978,58(1):149-163
We report a digital analysis of high-time-resolution videomagnetograms taken during a class 2b flare that occurred at 60° east. The data were obtained at the Big Bear Observatory and calibrated by a Mt. Wilson magnetogram. Changes of weak magnetic fields (less than 100 G) with an amplitude from 30 to 100% have been detected over 55% of the optical flare region, apparently taking place at the initial phase of the flare. Statistical considerations suggest a real flare association with most of these changes.H observations show that large changes took place over the footpoints of heavily inclined structures like penumbral fibrils, while smaller changes took place over the plage region. An apparent polarity reversal was found at the feet of erupted fibrils.Based on force-free field calculations these changes can be reasonably explained as a transformation of the current-carrying fields to potential fields which produced large changes in the field line inclination and rotation.Visiting Associate, Summer 1977. 相似文献
10.
The active region NOAA 6555 had several locations of highly sheared magnetic field structure, yet, only one of them was the site for all the five X-class flares during its disk passage in March 1991. The pre-flare observations of high-resolution H filtergrams, vector magnetograms and H Dopplergrams of the 2B/X5.3 flare on 25 March 1991 show that the flaring site was characterized by a new rising emerging flux region (EFR) near the highly sheared magnetic field configuration. The polarity axis of the emerging flux was nearly perpendicular to the pre-existing magnetic neutral line. The location of the EFR was the site of initial brightening in H. The post-flare magnetograms show higher magnetic shear at the flare location compared to the post-flare magnetograms, which might indicate that the EFR was sheared at the time of its emergence. As the new EFR coincided with the occurrence of the flare, we suggest that it might have triggered the observed flare. Observations from Big Bear Solar Observatory and Marshall Space Flight Center also show that there was emergence of new flux at the same location prior to two other X-class flares. We find that out of five observed X-class flares in NOAA 6555, at least in three cases there are clear signatures of flare-related flux emergence. Therefore, it is concluded that EFRs might play an important role in destabilizing the observed sheared magnetic structures leading to large X-class flares of NOAA 6555. 相似文献
11.
Hui Li Purple Mountain Observatory Chinese Academy of Sciences Nanjing National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2002,2(2):174-182
1 INTRODUCTION Magnetic field plays an important role in solar activity. The stressing and subsequent partialrelaxation of magnetic fields in the active regions are generally accepted to be the energy sourceof solar flares. To quantitatively study the extent of stressed magnetic field as distinct from itspotential field, Hagyard et al. (1984) defined a magnetic shear angle膖he azimuth differencebetween the observed transverse magnetic field vector and the computed potential field vectorth… 相似文献
12.
We investigate how the divergence-free property of magnetic fields can be exploited to resolve the azimuthal ambiguity present
in solar vector magnetogram data, by using line-of-sight and horizontal heliographic derivative information as approximated
from discrete measurements. Using synthetic data we test several methods that each make different assumptions about how the
divergence-free property can be used to resolve the ambiguity. We find that the most robust algorithm involves the minimisation
of the absolute value of the divergence summed over the entire field of view. Away from disk centre this method requires the
sign and magnitude of the line-of-sight derivatives of all three components of the magnetic field vector. 相似文献
13.
Using multi-wavelength data of Hinode, the rapid rotation of a sunspot in ac-tive region NOAA 10930 is studied in detail. We found extraordinary counterclockwise rotation of the sunspot with positive polarity before an X3.4 flare. From a series of vector magnetograms, it is found that magnetic force lines are highly sheared along the neu-tral line accompanying the sunspot rotation. Furthermore, it is also found that sheared loops and an inverse S-shaped magnetic loop in the corona formed gradually after the sunspot rotation. The X3.4 flare can be reasonably regarded as a result of this movement. A detailed analysis provides evidence that sunspot rotation leads to magnetic field linestwisting in the photosphere. The twist is then transported into the corona and triggers flares. 相似文献
14.
L. K. Harra C. H. Mandrini S. Dasso A. M. Gulisano K. Steed S. Imada 《Solar physics》2011,268(1):213-230
For large eruptions on the Sun, it is often a problem that the core dimming region cannot be observed due to the bright emission
from the flare itself. However, spectroscopic data can provide the missing information through the measurement of Doppler
velocities. In this paper we analyse the well-studied flare and coronal mass ejection that erupted on the Sun on 13 December
2006 and reached the Earth on 14 December 2006. In this example, although the imaging data were saturated at the flare site
itself, by using velocity measurements we could extract information on the core dimming region, as well as on remote dimmings.
The purpose of this paper is to determine more accurately the magnetic flux of the solar source region, potentially involved
in the ejection, through a new technique. The results of its application are compared to the flux in the magnetic cloud observed
at 1 AU, as a way to check the reliability of this technique. We analysed data from the Hinode EUV Imaging Spectrometer to estimate the Doppler velocity in the active region and its surroundings before and after the
event. This allowed us to determine a Doppler velocity ‘difference’ image. We used the velocity difference image overlayed
on a Michelson Doppler Imager magnetogram to identify the regions in which the blue shifts were more prominent after the event;
the magnetic flux in these regions was used as a proxy for the ejected flux and compared to the magnetic cloud flux. This
new method provides a more accurate flux determination in the solar source region. 相似文献
15.
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
16.
Moon Y.-J. Yun H.S. Lee S.W. Kim J.-H. Choe G.S. Park Y.D. Ai G. Zhang H.Q. Fang C. 《Solar physics》1999,184(2):323-338
In this paper we introduce a measure of magnetic field discontinuity, MAD, defined as Maximum Angular Difference between two adjacent magnetic field vectors. To examine the characteristics of the MAD, we have considered several active region models having a quadrupolar field configuration and computed MADs over these active regions by approximating the 3-D magnetic fields as an ensemble of charge potential fields or linear force-free fields. The computed MAD fields are studied in comparison with other flare activity indicators such as separators. It is found that (1) the region of high level MAD corresponds well with the separator, or practically the intersection of the separator with the plane of measurement, (2) it singles out local discontinuities of magnetic fields, and (3) the MAD can also be a measure of the evolutionary status of an active region.An observational test has been made for 2-D MADs, using the Yohkoh SXT observation of a flare in AR 6919 and the vector magnetogram taken at the Mees Solar Observatory during this flare activity. The high level contours of 2-D MAD are found to trace well the observed soft X-ray bright points, which indicates that the MAD could serve as a good flare activity indicator. 相似文献
17.
We study a flare which occurred on 3 November 1997 at 10:31 UT in the vicinity of a parasitic polarity of AR 8100. Using SOHO/EIT 195 Å observations, we identify the brightening of thin transequatorial loops connecting AR 8100 and AR 8102, and dimmings located between the two active regions. Difference images highlight the presence of a loop-like structure rooted near the flare location usually called an EIT wave. The coronal magnetic field derived from potential extrapolations from a SOHO/MDI magnetogram shows that the topology is complex near the parasitic polarity. There, a `bald patch' (defined as the locations where the magnetic field is tangent to the photosphere) is present. We conclude that the flare was a `bald patch flare'. Moreover, the extrapolation confirms that there is a large coronal volume filled with transequatorial field lines interconnecting AR 8100 and AR 8102, and overlaying the bald patch. We show that the dimmings are located at the footpoints of these large field lines, which can be also related to the thin bright loops observed during the flare. As this event was related to a coronal mass ejection (CME) observed by SOHO/LASCO, we propose that the observed dimmings are due to a decrease in plasma density during the opening of the transequatorial loops connecting both ARs. We propose a scenario where these large field lines are in fact pushed up by the opening of low-lying sheared field lines forming the bald patch. We finally discuss how the fast opening of these field lines can produce the brightening near the footpoints of the separatrix, observed as an `EIT wave'. 相似文献
18.
The finite energy force-free magnetic fields of the active region NOAA 9077 on 14 July 2000 above the photosphere were reconstructed. We study the evolution of the 3D magnetic field structures in AR 9077 and compare the reconstructed field lines with TRACE EUV 171 Å flare loops during the flare maximum, which confirms the process that flaring loops extended from lower sheared level to higher arcades. We also demonstrate the 3D magnetic field evolution before the 3B/X5.7 flare on 14 July and the magnetic structure after the flare on 15 July. This shows that the helical magnetic structures were significantly changed, suggesting that the flux rope was indeed erupted during the energetic flare at 10:24 UT on 14 July. 相似文献
19.
Ramesh Chandra Rajmal Jain Wahab Uddin Keiji Yoshimura Takeo Kosugi Taro Sakao Anita Joshi M. R. Deshpande 《Solar physics》2006,239(1-2):239-256
We present Hα observations from ARIES (Nainital) of a compact and impulsive solar flare that occurred on March 10, 2001 and
which was associated with a CME. We have also analyzed HXT, SXT/Yohkoh observations as well as radio observations from the Nobeyama Radio Observatory to derive the energetics and dynamics of this
impulsive flare. We coalign the Hα, SXR, HXR, MW, and magnetogram images within the instrumental spatial-resolution limit.
We detect a single HXR source in this flare, which is found spatially associated with one of the Hα bright kernels. The unusual
feature of HXR and Hα sources, observed for the first time, is the rotation during the impulsive phase in a clockwise direction.
We propose that the rotation may be due to asymmetric progress of the magnetic reconnection site or may be due to the change
of the peak point of the electric field. In MW emission we found two sources. The main source is at the main flare site and
another is in the southwest direction. It appears that the remote source is formed by the impact of accelerated energetic
electrons from the main flare site. From the spatial correlation of multiwavelength images of the different sources, we conclude
that this flare has a three-legged structure. 相似文献
20.
An X17 class (GOES soft X-ray) two-ribbon solar flare on October 28, 2003 is analyzed in order to determine the relationship
between the timing of the impulsive phase of the flare and the magnetic shear change in the flaring region. EUV observations
made by the Transition Region and Coronal Explorer (TRACE) show a clear decrease in the shear of the flare footpoints during the flare. The shear change stopped in the middle
of the impulsive phase. The observations are interpreted in terms of the splitting of the sheared envelope field of the greatly
sheared core rope during the early phase of the flare. We have also investigated the temporal correlation between the EUV
emission from the brightenings observed by TRACE and the hard X-ray (HXR) emission (E > 150 keV) observed by the anticoincidence system (ACS) of the spectrometer SPI on board the ESA INTEGRAL satellite. The
correlation between these two emissions is very good, and the HXR sources (RHESSI) late in the flare are located within the
two EUV ribbons. These observations are favorable to the explanation that the EUV brightenings mainly result from direct bombardment
of the atmosphere by the energetic particles accelerated at the reconnection site, as does the HXR emission. However, if there
is a high temperature (T > 20 MK) HXR source close to the loop top, a contribution of thermal conduction to the EUV brightenings cannot be ruled out. 相似文献