共查询到20条相似文献，搜索用时 15 毫秒
1.
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
2.
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
3.
S. -I. Akasofu 《Astrophysics and Space Science》1988,144(1-2):303-309
The presently prevailing theories of solar flares rely on the hypothetical presence of magnetic flux tubes beneath the photosphere and the two subsequent hypotheses, their emergence above the photosphere and explosive magnetic reconnection, converting magnetic energy carried by the flux tubes to solar flare energy. In this paper, we discuss solar flares from an entirely different point of view, namely in terms of power supply by a dynamo process in the photosphere. By this process, electric currents flowing along the magnetic field lines are generated and the familiar ‘force-free’ fields or the ‘sheared’ magnetic fields are produced. Upward field-aligned currents thus generated are carried by downward streaming electrons; these electrons can excite hydrogen atoms in the chromosphere, causing the optical Hα flares or ‘low temperature flares’. It is thus argued that as the ‘force-free’ fields are being built up for the magnetic energy storage, a flare must already be in progress. 相似文献
4.
The behaviour of the polar auroras in the dark part of the auroral oval during the solar flares has been examined. For the analysis 29 solar flares during spring and autumn periods when a part of the polar cap was sunlit were selected. It has been found that a sharp decreasing of the auroral arc luminosity occurred just after the solar flare onsets. Auroral arcs broke up into patches and in most cases disappeared in 2–3 min. Bright discrete auroras appeared again as a rule close to the maximum phase of the solar flares. The duration of polar aurora effects was typically from 4 to 13 min with median value of about 8 min. These effects have been observed inside the interval 18.00-04.00 M.L.T. during periods both of magnetic quiet and disturbance.For the large set of data magnetic field variations in the sunlit polar cap after the solar flare onset have been investigated. A simple model of the auroral processes for the qualitative explanation of the observed phenomenon has been suggested. 相似文献
5.
We investigate the periodic regimes of energy release on the Sun, namely, the recurrence of solar flares in active regions using the Solar Geophysical Data Journal on Hα flares from 1979 until 1981, which corresponds to the maximum of solar cycle 21. We obtained the following series of periods in the manifestation of flare activity bymeans of a correlation periodogram analysis, a self-similarity function, and a wavelet analysis: ～1, 2, 3 h as well as ～0.4, 1, 2, 5 days. We suggest a diffusive model for the quasi-periodic transfer of toroidal magnetic fields from under the photosphere to interpret the retrieved sequence of periods in the enhancement of flare activity. We estimated the typical spatial scales of the magnetic field variations in the solar convection zone: ～17 000 km. 相似文献
6.
B. V. Somov 《Solar System Research》2006,40(2):85-92
A review of current questions related to the problem of large solar flares is given. The basic physical principles applied in numerical simulation of flares are presented and illustrated. The main attention is given to the phenomenon of magnetic reconnection in large-scale current layers at separators of magnetic field in the corona. This phenomenon is demonstrated within the framework of the Rainbow topological model. The model provides the possibility of explaining specific features of large-scale reconnection as a physical process that makes it possible to accumulate large energy in the form of the magnetic energy of current layers before a flare and to quickly transform this energy to the kinetic energy of particles during a flare. The secondary effects in the solar atmosphere caused by energy fluxes from reconnecting current layers are also discussed. These consequences of the primary energy release are responsible for the flare pattern observed in X-ray, optical, UV, and other spectral ranges. 相似文献
7.
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
8.
G. W. Pneuman 《Solar physics》1967,2(4):462-483
The hypothesis that solar flares may be caused by a choking off of the normal energy flux to the corona by the strong closed magnetic fields of a plage is examined. If the energy flux into a plage from the photosphere is of the order of 108 ergs/cm2 sec, and if a substantial fraction of this energy is carried in the form of Alfvén waves, then the rate of dissipation of the waves is slower than the rate at which energy is injected. Since the waves must propagate along the magnetic field and cannot reenter the photosphere, they must remain within the plage; hence, the magnetic and kinetic energy in a small-scale motion (either waves, turbulence, or high-energy particles) must increase with time, eventually causing disruption of the volume when the small-scale energy density exceeds the energy in the mean field. It is believed that the unusually broad wings in the emission lines represent evidence of this phenomenon. The accumulation of waves is manifested as a resonance which occurs initially only at discrete locations in the magnetic field, but later is expected to involve the whole flare volume. The response of a typical volume of flare dimensions due to a trapping of the normal wave supply to the corona is studied through use of the virial equation. For magnetic fields typical of a plage, the region expands in a time scale of 102–103 sec, with a velocity in the neighborhood of 10–20 km/sec. Small-scale velocities within the region, however, have reached 100–300 km/sec, indicating that almost all the energy in the flare resides in small-scale forms. The energy density of the flare region exhibits a behavior much more explosive than the expansion rate. There is a rapid rise to maximum in 102 sec or less, and a slow subsequent decline taking about 103–104 sec due to the dilution of energy caused by expansion of the region. The predicted temporal behavior of the energy density coincides qualitatively with the light curves observed during flares, and it is suggested that the rise and decline of the energy density is to be associated with the optical flare. The total flare is defined as the time required for the energy density of the chromosphere and corona to return to the pre-flare state. During this time (about one hour) a large flare can derive the necessary 1032 ergs from normal photospheric energy output. 相似文献
9.
B. V. Somov 《Astronomy Letters》2010,36(7):514-519
In connection with the RHESSI satellite observations of solar flares, which have revealed new properties of hard X-ray sources
during flares, we offer an interpretation of these properties. The observed motions of coronal and chromospheric sources are
shown to be the consequences of three-dimensional magnetic reconnection at the separator in the corona. During the first (initial)
flare phase, the reconnection process releases an excess of magnetic energy related predominantly to themagnetic tensions
produced before the flare by shear plasma flows in the photosphere. The relaxation of a magnetic shear in the corona also
explains the downward motion of the coronal source and the decrease in the separation between chromospheric sources. During
the second (main) flare phase, ordinary reconnection dominates; it describes the energy release in the terms of the “standard
model” of large eruptive flares accompanied by the rise of the coronal source and an increase in the separation between chromospheric
sources. 相似文献
10.
《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
11.
Yohkoh observations strongly suggest that electron acceleration in solar flares occurs in magnetic reconnection regions in the corona above the soft X-ray flare loops. Unfortunately, models for particle acceleration in reconnecting current sheets predict electron energy gains in terms of the reconnection electric field and the thickness of the sheet, both of which are extremely difficult to measure. It can be shown, however, that application of Ohm's law in a turbulent current sheet, combined with energy and Maxwell's equations, leads to a formula for the electron energy gain in terms of the flare power output, the magnetic field strength, the plasma density and temperature in the sheet, and its area. Typical flare parameters correspond to electron energies between a few tens of keV and a few MeV. The calculation supports the viewpoint that electrons that generate the continuum gamma-ray and hard X-ray emissions in impulsive solar flares are accelerated in a large-scale turbulent current sheet above the soft X-ray flare loops. 相似文献
12.
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
13.
Solar eruptions are the most spectacular events in our solar system and are associated with many different signatures of energy release including solar flares, coronal mass ejections, global waves, radio emission and accelerated particles. Here, we apply the Coronal Pulse Identification and Tracking Algorithm (CorPITA) to the high-cadence synoptic data provided by the Solar Dynamics Observatory (SDO) to identify and track global waves observed by SDO. 164 of the 362 solar flare events studied (45%) were found to have associated global waves with no waves found for the remaining 198 (55%). A clear linear relationship was found between the median initial velocity and the acceleration of the waves, with faster waves exhibiting a stronger deceleration (consistent with previous results). No clear relationship was found between global waves and type II radio bursts, electrons or protons detected in situ near Earth. While no relationship was found between the wave properties and the associated flare size (with waves produced by flares from B to X-class), more than a quarter of the active regions studied were found to produce more than one wave event. These results suggest that the presence of a global wave in a solar eruption is most likely determined by the structure and connectivity of the erupting active region and the surrounding quiet solar corona rather than by the amount of free energy available within the active region. 相似文献
14.
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
15.
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
16.
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
17.
E. Schatzman 《Solar physics》1967,1(3-4):411-419
Some ideas are developed concerning solar flares which have been presented earlier by the author (Schatzman, 1966a). Emphasis is laid on the problem of energy transport; from the energy supply to the region of the optical flare, on the storage of low energy cosmic ray particles in a magnetic bottle before the beginning of the optical flare, and the mechanism which triggers both the optical flare, and the production of high-energy cosmic rays. The relation between solar and stellar flares is considered.Lecture given at Goddard Space Flight Center, November 4, 1966. 相似文献
18.
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
19.
Kocharov L. G. Torsti J. Tang F. Zirin H. Kovaltsov G. A. Usoskin I. G. 《Solar physics》1997,172(1-2):271-278
This paper demonstrates the important interplanetary manifestation of strongly tilted magnetic fields at the flare site. We start with analysis of Big Bear Solar Observatory (BBSO) observations of magnetic structures at sites of two flares responsible for >100 MeV neutron events. Based on these observations, a model of neutron production is considered. This model takes into account the observed large tilt of magnetic field lines at footpoints of flare magnetic loops. Results of the new calculations are compared with both previous calculations and observations. The tilt of magnetic field lines at the flare site is proved to be the most important parameter limiting anisotropy of high-energy secondary emission in solar flares. 相似文献
20.
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