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1.
Sara F. Martin 《Solar physics》1989,121(1-2):215-238
Mass motions are a principal means by which components of solar flares can be distinguished. Typical patterns of mass motions in H are described for chromospheric flare ribbons, remote chromospheric flare patches, flare loops, flaring arches, surges, erupting filaments and some expanding coronal features. Interrelationships between these phenomena are discussed and illustrations of each are presented.  相似文献   

2.
We report a detailed examination about the relationship between the evolution of the Hα flare ribbons and the released magnetic energy during the April 10 2001 flare. In the Hα images, several bright kernels are observed in the flare ribbons. We identified the conjugated foot-points, by analyzing the lightcurves at each Hα kernels, and showed their connectivities during the flare. Then, based on the magnetic reconnection model, we calculated quantitatively the released energy by using the photospheric magnetic field strengths and separation speeds of the Hα flare ribbons. Finally, we examined the downward motions which are observed at the Hα kernels. We found that the stronger the red-asymmetry tends to be associated with the brighter the Hα kernel.  相似文献   

3.
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   

4.
We present a technique for automatic determination of flare ribbon separation and the energy released during the course of two-ribbon flares. We have used chromospheric Hα filtergrams and photospheric line-of-sight magnetograms to analyse flare ribbon separation and magnetic field structures, respectively. Flare ribbons were first enhanced and then extracted by the technique of “region growing”, i.e., a morphological operator to help resolve the flare ribbons. Separation of flare ribbons was then estimated from the magnetic-polarity reversal line using an automatic technique implemented into an Interactive Data Language (IDLTM) platform. Finally, the rate of flare-energy release was calculated using photospheric magnetic field data and the corresponding separation of the chromospheric Hα flare ribbons. This method could be applied to measure the motion of any feature of interest (e.g., intensity, magnetic, Doppler) from a given point of reference.  相似文献   

5.
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   

6.
We reinvestigate the problem of Hα intensity oscillations in large flares, particularly those classified as X-class flares. We have used high spatial and temporal resolution digital observations obtained from Udaipur Solar Observatory during the period 1998–2006 and selected several events. Normalized Lomb-Scargle periodogram method for spectral analysis was used to study the oscillatory power in quiet and active chromospheric locations, including the flare ribbons.  相似文献   

7.
We carried out an electromagnetic acoustic analysis of the solar flare of 14 August 2004 in active region AR10656 from the radio to the hard X-ray spectrum. The flare was a GOES soft X-ray class M7.4 and produced a detectable sun quake, confirming earlier inferences that relatively low energy flares may be able to generate sun quakes. We introduce the hypothesis that the seismicity of the active region is closely related to the heights of coronal magnetic loops that conduct high-energy particles from the flare. In the case of relatively short magnetic loops, chromospheric evaporation populates the loop interior with ionised gas relatively rapidly, expediting the scattering of remaining trapped high-energy electrons into the magnetic loss cone and their rapid precipitation into the chromosphere. This increases both the intensity and suddenness of the chromospheric heating, satisfying the basic conditions for an acoustic emission that penetrates into the solar interior.  相似文献   

8.
Solar flares with a broadband emission in the white-light range of the electromagnetic spectrum belong to most enigmatic phenomena on the Sun. The origin of the white-light emission is not entirely understood. We aim to systematically study the visible-light emission connected to solar flares in SDO/HMI observations. We developed a code for automatic detection of kernels of flares with HMI intensity brightenings and study properties of detected candidates. The code was tuned and tested and with a little effort, it could be applied to any suitable data set. By studying a few flare examples, we found indication that HMI intensity brightening might be an artefact of the simplified procedure used to compute HMI observables.  相似文献   

9.
The impulsive phase of the 23 July 2002 2B/X4.8 proton flare with a classical two-ribbon structure was observed with the Irkutsk Large Solar Vacuum Telescope (LSVT) in spectropolarimetric mode, with high spatial, spectral, and time resolution. On the basis of 49 spectrograms and 1200 spectral cuts across the flare ribbons, evidence for Hα line impact polarization has been obtained. A systematic change of the Stokes Q and U parameters has been detected across the ribbons for different flare regions measured with a scanning step of 0.85″. In the eastern side of the ribbons, the degree of polarization is 4 – 8%; its plane is oriented toward the solar disk center (radial direction). In the western side, the polarization degree runs up to 25%, and its plane is perpendicular to the disk center direction (tangential direction). A comparison of these results with hard X-ray data (RHESSI) allows us to conclude that high-energy electron beams reached the chromosphere during this flare. The observed changes of the direction of polarization and the vanishing polarization within the ribbons mean that, at the chromospheric level, the energy of electrons remaining in the beam is about 200 eV. A shift of the peak position of polarization relative to the intensity maximum in the ribbons may result from the inclination of the electron beam axis with respect to the solar surface.  相似文献   

10.
We analyzed the monochromatic Hα and spectral (within a range of 6549–6579 Å) observational data for the 2B/X6.9 flare of August 9, 2011, that produced emission in the optical continuum. The morphology and evolution of the Hα flare and the position, time evolution, spectrum, and energetics of the white-light flare (WLF) kernels were studied. The following results were obtained: the flare erupted in the region of collision of a new and rapidly growing and propagating magnetic flux and a preexisting one. This collision led to a merger of two active bipolar regions. The white-light flare had a complex structure: no less than five kernels of continuum emission were detected prior to and in the course of the impulsive flare phase. Preimpulsive and impulsive white-light emission kernels belonged to different types (types II and I, respectively) of white-light flares. A close temporal agreement between the white-light emission maxima and the microwave emission peak was observed for the impulsive white-light emission kernels. The maximum flux, luminosity, and total energy emitted by the brightest impulsive WLF kernel equaled 1.4 × 1010 ergs cm?2 s?1, 1.5 × 1027 ergs/s, and 5 × 1029 ergs, respectively. The Hα profiles within the impulsive WLF kernels had broad wings (with a total extent of up to 26 Å and a half-width of up to 9 Å) and self-reversed cores. The profiles were symmetrical, but were shifted towards the red side of the spectrum. This is indicative of a downward motion of the entire emitting volume with a radial velocity of several tens of km/s. The intensity pattern in the wings did not correspond to the Stark one. The profiles were broadened by nonthermal turbulent motions with velocities of 150–300 km/s. The observed Hα profiles were analyzed and compared in their features to the profiles calculated for an intense heating of the chromosphere by nonthermal electrons accompanied by the development of a chromospheric condensation propagating downward. We came to the conclusion that the analyzed flare exhibited spectral features that may not be readily explained within the framework of chromosphere heating by a beam of nonthermal electrons.  相似文献   

11.
A multi-wavelength spatial and temporal analysis of solar high-energy electrons is conducted using the August 20, 2002 flare of an unusually flat (γ1 = 1.8) hard X-ray spectrum. The flare is studied using RHESSI, Hα, radio, TRACE, and MDI observations with advanced methods and techniques never previously applied in the solar flare context. A new method to account for X-ray Compton backscattering in the photosphere (photospheric albedo) has been used to deduce the primary X-ray flare spectra. The mean electron flux distribution has been analysed using both forward fitting and model-independent inversion methods of spectral analysis. We show that the contribution of the photospheric albedo to the photon spectrum modifies the calculated mean electron flux distribution, mainly at energies below ∼100 keV. The positions of the Hα emission and hard X-ray sources with respect to the current-free extrapolation of the MDI photospheric magnetic field and the characteristics of the radio emission provide evidence of the closed geometry of the magnetic field structure and the flare process in low altitude magnetic loops. In agreement with the predictions of some solar flare models, the hard X-ray sources are located on the external edges of the Hα emission and show chromospheric plasma heated by the non-thermal electrons. The fast changes of Hα intensities are located not only inside the hard X-ray sources, as expected if they are the signatures of the chromospheric response to the electron bombardment, but also away from them.  相似文献   

12.
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   

13.
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   

14.
The M7.7 solar flare of July 19, 2012, at 05:58 UT was observed with high spatial, temporal, and spectral resolutions in the hard X-ray and optical ranges. The flare occurred at the solar limb, which allowed us to see the relative positions of the coronal and chromospheric X-ray sources and to determine their spectra. To explain the observations of the coronal source and the chromospheric one unocculted by the solar limb, we apply an accurate analytical model for the kinetic behavior of accelerated electrons in a flare. We interpret the chromospheric hard X-ray source in the thick-target approximation with a reverse current and the coronal one in the thin-target approximation. Our estimates of the slopes of the hard X-ray spectra for both sources are consistent with the observations. However, the calculated intensity of the coronal source is lower than the observed one by several times. Allowance for the acceleration of fast electrons in a collapsing magnetic trap has enabled us to remove this contradiction. As a result of our modeling, we have estimated the flux density of the energy transferred by electrons with energies above 15 keV to be ～5 × 1010 erg cm?2 s?1, which exceeds the values typical of the thick-target model without a reverse current by a factor of ～5. To independently test the model, we have calculated the microwave spectrum in the range 1–50 GHz that corresponds to the available radio observations.  相似文献   

15.
Z. Švestka 《Solar physics》1973,31(2):389-400
The assumption that the flare originates in the corona or transition layer, is confronted with the known properties of chromospheric flares. It is concluded that the basic mode of the energy transport into chromosphere is heat conduction. Only in some flares non-thermal particles contribute to the brightening in lower atmospheric layers: electrons with energy close to 100 keV produce chromospheric bright patches, and protons above 20 MeV cause the photospheric enhancements. The particle-produced brightenings are superposed on the basic quasi-thermal flare and involve only small areas as compared with the extensive regions heated through conduction.The most probable height of the flare origin appears to be close to the transition layer, between some 4000 and 7000 km above the photosphere. The non-thermal acceleration (when present) occurs probably higher than where the flare originates. There is no obvious reason why the high electron density in chromospheric flares could not be explained as simply due to increased ionization in the existing plasma, without any flare-induced mass condensations.Though there are several facts supporting the flare origin in the corona (or transition layer), one cannot exclude the alternative that the flare instability involves simultaneously a wide (and in different cases different) range of altitudes. Energy considerations give some support to such a supposition.Mitteilungen aus dem Fraunhofer Institut Nr. 121.Visiting scientist at the Fraunhofer Institute, grant of Stifterverband für die Deutsche Wissenschaft.  相似文献   

16.
Fletcher  L.  Hudson  H. 《Solar physics》2001,204(1-2):69-89
The `ribbons' of two-ribbon flares show complicated patterns reflecting the linkages of coronal magnetic field lines through the lower solar atmosphere. We describe the morphology of the EUV ribbons of the July 14, 2000 flare, as seen in SOHO, TRACE, and Yohkoh data, from this point of view. A successful co-alignment of the TRACE, SOHO/MDI and Yohkoh/HXT data has allowed us to locate the EUV ribbon positions on the underlying field to within ∼ 2′′, and thus to investigate the relationship between the ribbons and the field, and also the sites of electron precipitation. We have also made a determination of the longitudinal magnetic flux involved in the flare reconnection event, an important parameter in flare energetic considerations. There are several respects in which the observations differ from what would be expected in the commonly-adopted models for flares. Firstly, the flare ribbons differ in fine structure from the (line-of-sight) magnetic field patterns underlying them, apparently propagating through regions of very weak and probably mixed polarity. Secondly, the ribbons split or bifurcate. Thirdly, the amount of line-of-sight flux passed over by the ribbons in the negative and positive fields is not equal. Fourthly, the strongest hard X-ray sources are observed to originate in stronger field regions. Based on a comparison between HXT and EUV time-profiles we suggest that emission in the EUV ribbons is caused by electron bombardment of the lower atmosphere, supporting the hypothesis that flare ribbons map out the chromospheric footpoints of magnetic field lines newly linked by reconnection. We describe the interpretation of our observations within the standard model, and the implications for the distribution of magnetic fields in this active region.  相似文献   

17.
We present the results of studying the proton flare 2B/X4.8 on 23 July 2002, observed with the Large Solar Vacuum Telescope (LSVT) at the Baikal Astrophysical Observatory in spectropolarimetric mode with high spatial and spectral resolution. We have found some evidence for H?? line impact linear polarization, predominantly during the initial moments of the flare. For the H?? line 606 cuts were made along the dispersion in 53 spectrograms, and a polarization signal was found more or less confidently in 60 cuts (13 spectrograms). Polarization was mainly observed in one of the kernels of the flare. A particular feature of this kernel was that the H?? line was observed to show a reversal in the central part of this kernel, which created a dip in the kernel center in the photometric cut. The size of these dips and the size of the sites with the linear polarization coincide and are equal to 3??C?6?arcsec. The maximum polarization degree in this kernel reached 15?%. The direction of the polarization in the kernel is radial, except for the first two frames, where the direction of the polarization was both radial and tangential. Furthermore, we found an analogy between the effects observed at the chromospheric level in this kernel (polarization and depression in H?? line) and the temporal variation of the HXR sources.  相似文献   

18.
A solar flare on June 15, 1973 has been observed with high spatial and temporal resolution by the S-054 grazing-incidence X-ray telescope on Skylab. Both morphological and quantitative analyses are presented. Some of the main results are: (a) the overall configuration of the flare is that of a compact region with a characteristic size of the order of 30 at the intensity peak, (b) this region appears highly structured inside with complex systems of loops which change during the event, (c) a brightening over an extended portion of the active region precedes the flare onset, (d) the impulsive phase indicated by the non-thermal radio emission is a period during which a rapid brightening occurs in loop structures, (e) the X-ray emission is centered over the neutral line of longitudinal magnetic field, and the brightest structures at the flare onset bridge the neutral line, (f) loop systems at successively increasing heights form during the decay phase, finally leading to the large loops observed in the postflare phase, (g) different parts of the flare show distinctly different light curves, and the temporal development given by full disk detectors is the result of integrating the different intensity vs time profiles.The implications of these observations for mechanisms of solar flares are discussed. In particular, the flux profiles of different regions of the flare give strong evidence for continued heating during the decay phase, and a multiplicity of flare volumes appears to be present, in all cases consisting of loops of varying lengths.On leave from Arcetri Astrophysical Observatory, Florence, Italy.  相似文献   

19.
Huaning  WANG 《Solar physics》1997,174(1-2):265-279
We extrapolated the 3-D fields above the photosphere, taking the observed photospheric magnetic fields in the active regions NOAA 6659 and 7321 as the boundary conditions of a linear force-free field model, and detected the singular points of the 2-D fields in a plane at the chromospheric level. These singular points can be described with the Poincaré index. Singular points with the index of +1 correspond to concentrations of magnetic flux, and those with the index of -1 to the saddle points in the plane. All of these singular points are connected by the lanes demarcating the 2-D magnetic cells in the plane. It has been confirmed that these saddle points are the intersections between separators and planes intersecting the 3-D fields. From comparisons between kernels of flares occurring in both regions and the saddle points, we found that there is a close morphological relationship between distributions of the saddle points and flare kernels. The main results are as follows: (a) The flare kernels tend to appear in areas with concentrating 2-D saddle points. (b) The morphology of the kernels is exactly confined by the lanes in the plane at chromospheric level. These facts seem favourable for the viewpoint that solar flares are closely related to magnetic separatrices and separators.  相似文献   

20.
Tracking of TRACE Ultraviolet Flare Footpoints   总被引：1，自引：0，他引：1  
Solar flares produce bright, compact sources of UV emission in the lower atmosphere, identified as flare footpoints. Observed at high time cadence with the Transition Region and Coronal Explorer, groups of UV footpoints define flare `ribbons' which move as the flare progresses. We have developed a procedure to track individual bright kernels within flare ribbons, enabling us to study the motion of these sites of excitation through the solar chromosphere. We have applied this to a flare observed by TRACE in the 1600 Å passband at 2-s cadence. In this event, the footpoints have an average speed of 15 km s–1, with a superposed random `meandering' component, consistent with the footpoint magnetic field being anchored around the edges of granular cells. Examining the brightness as a function of time, we find that the timing of peaks in brightness is significantly correlated with the timing of peaks in the product of the footpoint speed with the line-of-sight magnetic field strength at the footpoint location; in other words with a measure of the coronal reconnection rate.  相似文献   

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