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1.
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
2.
The claim by Pudovkin and his co-workers that the geomagnetic effects of a solar flare are controlled almost exclusively by the direction of the large scale magnetic field at the flare site is in apparent conflict with the well established correlation between flares with type IV radio bursts and subsequent geomagnetic storms. We examine the claims of Pudovkin et al., and show that while the direction of the magnetic field is important in determining the geomagnetic effect of a flare, it is not as important as an accompanying type IV burst. 相似文献
3.
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
4.
B. V. Somov 《Astronomy Letters》2012,38(2):128-138
The role of the electric currents distributed over the volume of an active region on the Sun is considered from the standpoint
of solar flare physics. We suggest including the electric currents in a topological model of the magnetic field in an active
region. Typical values of the mutual inductance and the interaction energy of the coronal electric currents flowing along
magnetic loops have been estimated for the M7/1N flare on April 27, 2006. We show that if these currents actually make a significant
contribution to the flare energetics, then they must manifest themselves in the photosphericmagnetic fields. Depending on
their orientation, the distributed currents can both help and hinder reconnection in the current layer at the separator during
the flare. Asymmetric reconnection of the currents is accompanied by their interruption and an inductive change in energy.
The reconnection of currents in flares differs significantly from the ordinary coalescence instability of magnetic islands
in current layers. Highly accurate measurements of the magnetic fields in active regions are needed for a quantitative analysis
of the role of distributed currents in solar flares. 相似文献
5.
Solar flares release large amounts of energy at different layers of the solar atmosphere, including at the photosphere in the case of exceptionally major events. Therefore, it is expected that large flares would be able to excite acoustic waves on the solar surface, thereby affecting the p-mode oscillation characteristics. We have applied the ring-diagram analysis technique to 3-D power spectra obtained for different flare regions in order to study how flares affect the amplitude, frequency and width of the acoustic modes. Data from the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO) has been used. We have used data obtained for several active regions of the current solar cycle that have produced flares. In most cases, during the period of high flare activity, power in p modes appears to be larger when compared to that in non-flaring regions of similar magnetic field strength. 相似文献
6.
Solar flares are powered by the energy stored in magnetic fields, so evolutionary information of the magnetic field is important
for short-term prediction of solar flares. However, the existing solar flare prediction models only use the current information
of the active region. A sequential supervised learning method is introduced to add the evolutionary information of the active
region into a prediction model. The maximum horizontal gradient, the length of the neutral line, and the number of singular
points extracted from SOHO/MDI longitudinal magnetograms are used in the model to describe the nonpotentiality and complexity
of the photospheric magnetic field. The evolutionary characteristics of the predictors are analyzed by using autocorrelation
functions and mutual information functions. The analysis results indicate that a flare is influenced by the 3-day photospheric
magnetic field information before flare eruption. A sliding-window method is used to add evolutionary information of the predictors
into machine learning algorithms, then C4.5 decision tree and learning vector quantization are employed to predict the flare
level within 48 hours. Experimental results indicate that the performance of the short-term solar flare prediction model within
the sequential supervised learning framework is significantly improved. 相似文献
7.
This paper reviews studies of the relationship between the evolution of vector magnetic fields and the occurrence of major solar flares. Most of the data were obtained by the video magnetograph systems at Big Bear Solar Observatory (BBSO) and Huairou Solar Observatory (HSO). Due to the favorable weather and seeing conditions at both stations, high-resolution vector magnetograph sequences of many active regions that produced major flares during last solar maximum (1989–1993) have been recorded. We have analyzed several sequences of magnetograms to study the evolution of vector magnetic fields of flare productive active regions. The studies have focused on the following three aspects: (1) processes which build up magnetic shear in active regions; (2) the pre-flare magnetic structure of active regions; and (3) changes of magnetic shear immediately preceding and following major flares. We obtained the following results based on above studies: (1) Emerging flux regions (EFRs) play very important roles in the production of complicated photospheric flow patterns, magnetic shear and flares. (2) Although the majority of flares prefer to occur in magnetically sheared regions, many flares occurred in regions without strong photospheric magnetic shear. (3) We found that photospheric magnetic shear increased after all the 6 X-class flares studied by us. We want to emphasize that this discovery is not contradictory to the energy conservation principle, because a flare is a three-dimensional process, and the photosphere only provides a two-dimensional boundary condition. This argument is supported by the fact that if two initial ribbons of a flare are widely separated (which may correspond to a higher-altitude flare), the correlation of the flare with strong magnetic shear is weak; if the two ribbons of a flare are close (which may correspond to a lower-altitude flare), its correlation with the strong shear is strong. (4) We have analyzed 18 additional M-class flares observed by HSO in 1989 and 1990. No detectable shear change was found for all the cases. It is likely that only the most energetic flares can affect the photospheric magnetic topology. 相似文献
8.
The energy source of a flare is the magnetic field in the corona. A topological model of the magnetic field is used here for interpreting the recently discovered drastic changes in magnetic field associated with solar flares. The following observational results are self‐consistently explained: (1) the transverse field strength decreases at outer part of active regions and increases significantly in their centers; (2) the center‐of‐mass positions of opposite magnetic polarities converge towards the magnetic neutral line just after flares onset; (3) the magnetic flux of active regions decreases steadily during the course of flares. For X‐class flares, almost 50% events show such changes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
9.
Martin D. Altschuler 《Solar physics》1976,47(1):183-192
Recent Skylab and magnetograph observations indicate that strong photospheric electric currents underlie small flare events such as X-ray loops and surges. What is not yet certain, because of the non-local dynamics of a fluid with embedded magnetic field, is whether flare emission derives from the energy of on-site electric currents or from energy which is propagated to the flare site through an intermediary, such as a stream of fast electrons or a group of waves. Nevertheless, occurrences of: (1) strong photospheric electric currents beneath small flares; (2) similar magnetic fine structure inside and outside active regions; (3) eruptive prominences and coronal white light transients in association with big flares; and, (4) active boundaries of large unipolar regions suggest the possibility that all phenomena of solar activity are manifestations of the rapid ejection and/or gradual removal of electric currents of various sizes from the photosphere. The challenge is to trace the precise magnetofluid dynamics of each active phenomenon, particularly the role of electric current build-up and dissipation in the low corona. 相似文献
10.
T. J. Janssens 《Solar physics》1972,27(1):149-163
Using a newly developed Aerospace digital videomagnetograph, three solar active regions are studied as to their magnetic configurations and their flare productivity. These three regions have very different types of magnetic configurations and different types of flare productivity. We review previous theoretical and experimental research on flares and magnetic energy storage, and discuss various ways to observe magnetic energy release due to flares. Results for six subflares are presented. Five showed no measurable magnetic energy change and one result is questionable.We show three counterexamples to Zirin's (1972) contention that as a rule H plage brightness is proportional to magnetic field strength. Each of these three cases involved two plage regions of the same polarity and equal field strengths with one of the plages adjacent to a neutral line. In all three cases the plage region nearer the neutral line was much brighter. 相似文献
11.
By analysing the relationship between flares and the morphology of velocity and magnetic fields in active regions AR 5528,
AR 5629, and AR 6891, we found that initial brightening points at the earliest phase and flare ribbons at the maximum phase
are more closely related to the velocity field patterns than to magnetic field patterns. We also found that the velocity patterns
related to the flares are different from Evershed flows in the chromosphere. Finally, a model of vortex-induced reconnection
has been applied to solar flares and some preliminary results are discussed. 相似文献
12.
《天文和天体物理学研究(英文版)》2017,(9)
With SDO observations and a data-constrained magnetohydrodynamics(MHD)model,we identify a confined multi-ribbon flare that occurred on 2010 October 25 in solar active region 11117 as a magnetic bald patch(BP)flare with strong evidence.From the photospheric magnetic field observed by SDO/HMI,we find there are indeed magnetic BPs on the polarity inversion lines(PILs)which match parts of the flare ribbons.From the 3D coronal magnetic field derived from an MHD relaxation model constrained by the vector magnetograms,we find strikingly good agreement of the BP separatrix surface(BPSS)footpoints with the flare ribbons,and the BPSS itself with the hot flaring loop system.Moreover,the triggering of the BP flare can be attributed to a small flux emergence under the lobe of the BPSS,and the relevant change of coronal magnetic field through the flare is reproduced well by the pre-flare and post-flare MHD solutions,which match the corresponding pre-and post-flare AIA observations,respectively.Our work contributes to the study of non-typical flares that constitute the majority of solar flares but which cannot be explained by the standard flare model. 相似文献
13.
本文利用紫金山天文台太阳光谱仪缝前附属Ｄａｙｓｔａｒ滤光器拍摄的，发生在ＮＯＡＡ５３９５活动区中的三个耀斑的Ｈα单色光资料，对比北京天文台怀柔观测站取得的光球磁场资料，研究耀斑产生位置与光球磁场演化的关系，结果表明：（１）在所研究的５０个耀斑亮核中，有３８个位于新浮磁流区附近，另有少数亮核出现在磁对消区；（２）耀斑亮核多集中在横场方向交叉，剪切角大的复杂磁区，耀斑后多数区域磁场结构简化；（３）耀斑 相似文献
14.
ＡＲ６６５９是２２周以来最重要的一个活动区，它爆发了２２周最强大的高能事件。本文用云南天文台的光球、色球精细结构照片和北京天文台怀柔站的磁场速度场资料，分析了该活动区磁场速度场的二维位形和大耀斑期间的演化特征。本文分析的４个大耀斑均爆发在中性线附近的Ｎ极区磁场梯度大的地方及色球速度场的红移区。偏带观测也显示耀斑物质是向红端移动的。耀斑波沿横场传播在离本黑子群几万至十几万公里的地方激起感生耀斑，在原生耀斑与感生耀斑之间往往有耀斑环相连。此外，本文还从演化特征出发分析了耀斑爆发前活动区等离子体的宏观不稳定性。 相似文献
15.
M. R. Kundu S. M. White V. I. Garaimov P. Subramanian S. Ananthakrishnan P. Janardhan 《Solar physics》2006,236(2):369-387
Observations of a solar flare at 617 MHz with the Giant Meter-wave Radio Telescope (GMRT) are used to study the morphology
of flare radio emission at decimetric wavelengths. There has been very little imaging in the 500 – 1000 MHz frequency range,
but it is of great interest, since it corresponds to densities at which energy is believed to be released in solar flares.
This event has a very distinctive morphology at 617 MHz: the radio emission is clearly resolved by the 30″ beam into arc-shaped
sources seeming to lie at the tops of long loops, anchored at one end in the active region in which the flare occurs, with
the other end lying some 200 000 km away in a region of quiet solar atmosphere. Microwave images show fairly conventional
behaviour for the flare in the active region: it consists of two compact sources overlying regions of opposite magnetic polarity
in the photosphere. The decimetric emission is confined to the period leading up to the impulsive phase of the flare, and
does not extend over a wide frequency range. This fact suggests a flare mechanism in which the magnetic field at considerable
height in the corona is destabilized a few minutes prior to the main energy release lower in the corona. The radio morphology
also suggests that the radiating electrons are trapped near the tops of magnetic loops, and therefore may have pitch angles
near 90˚. 相似文献
16.
Maria D. Kazachenko Richard C. Canfield Dana W. Longcope Jiong Qiu 《Solar physics》2012,277(1):165-183
In order to better understand the solar genesis of interplanetary magnetic clouds (MCs), we model the magnetic and topological
properties of four large eruptive solar flares and relate them to observations. We use the three-dimensional Minimum Current Corona model (Longcope, 1996, Solar Phys.
169, 91) and observations of pre-flare photospheric magnetic field and flare ribbons to derive values of reconnected magnetic
flux, flare energy, flux rope helicity, and orientation of the flux-rope poloidal field. We compare model predictions of those
quantities to flare and MC observations, and within the estimated uncertainties of the methods used find the following: The
predicted model reconnection fluxes are equal to or lower than the reconnection fluxes inferred from the observed ribbon motions.
Both observed and model reconnection fluxes match the MC poloidal fluxes. The predicted flux-rope helicities match the MC
helicities. The predicted free energies lie between the observed energies and the estimated total flare luminosities. The
direction of the leading edge of the MC’s poloidal field is aligned with the poloidal field of the flux rope in the AR rather
than the global dipole field. These findings compel us to believe that magnetic clouds associated with these four solar flares
are formed by low-corona magnetic reconnection during the eruption, rather than eruption of pre-existing structures in the
corona or formation in the upper corona with participation of the global magnetic field. We also note that since all four
flares occurred in active regions without significant pre-flare flux emergence and cancelation, the energy and helicity that
we find are stored by shearing and rotating motions, which are sufficient to account for the observed radiative flare energy
and MC helicity. 相似文献
17.
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
18.
A topological model with magnetic reconnection at two separators in the corona is used to account for the recently discovered changes of the photospheric magnetic field in the active region NOAA 9077 during the July 14, 2000 flare. The model self-consistently explains the following observed effects: (1) the magnetic field strength decreases on the periphery of the active region but increases in its inner part near the neutral line of the photospheric magnetic field; (2) the center-of-mass positions of the fields of opposite (northern and southern) polarities converge; and (3) the magnetic flux of the active region decreases after the flare. The topological model gives not only a qualitative interpretation of the flare phenomena (the structure of the interacting magnetic fluxes in the corona, the location of the energy sources, the shape of the flare ribbons and kernels in the chromosphere and photosphere), but also correct quantitative estimates of the large-scale processes that form the basis for solar flares. The electric field emerging in the flare during large-scale reconnection is calculated. The electric field strength correlates with the observed intensity of the hard X-ray bremsstrahlung, suggesting an electron acceleration as a result of reconnection. 相似文献
19.
We study the association of type III bursts related to H flares in different magnetic environments in the period 1970–1981. Special attention is paid to flares which partly cover a major spot umbra (Z-flares). In particular we consider the location of the spots in the active regions and the magnetic field intensities of spots covered by a ribbon. The association rate with type III bursts decreases to 17% when the flare is located inside the bipolar pattern of a large active region, compared with an association rate of 54% when the flare is situated outside it. The association rate increases with the magnetic field intensity of the spot covered by H emission; this is most clearly revealed for the flares occurring outside the bipolar pattern of active regions. Ninety-three percent of the flare-associated type III burst were accompanied by 10 cm radio bursts. For the most general case in which a flare is developing anywhere in an active region, the association with type III bursts generation increases with the increasing magnetic field intensity of the main spot of the group. 相似文献
20.
Based on a topological model for the magnetic field of a solar active region (AR), we suggest a criterion for the existence of magnetic null points on the separators in the corona. With the problem of predicting solar flares in mind, we have revealed a model parameter whose decrease means that the AR evolves toward a major eruptive flare. We analyze the magnetic field evolution for AR 9077 within two days before the Bastille Day flare on July 14, 2000. The coronal conditions are shown to have become more favorable for magnetic reconnection, which led to a 3B/X5.7 eruptive flare. 相似文献