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1.
Following the discovery of a few significant seismic sources at 6.0 mHz from the large solar flares of October 28 and 29, 2003, we have extended SOHO/MDI helioseismic observations to moderate M-class flares. We report the detection of seismic waves emitted from the β γ δ active region NOAA 9608 on September 9, 2001. A quite impulsive solar flare of type M9.5 occurred from 20:40 to 20:48 UT. We used helioseismic holography to image seismic emission from this flare into the solar interior and computed time series of egression power maps in 2.0 mHz bands centered at 3.0 and 6.0 mHz. The 6.0 mHz images show an acoustic source associated with the flare some 30 Mm across in the East – West direction and 15 Mm in the North – South direction nestled in the southern penumbra of the main sunspot of AR 9608. This coincides closely with three white-light flare kernels that appear in the sunspot penumbra. The close spatial correspondence between white-light and acoustic emission adds considerable weight to the hypothesis that the acoustic emission is driven by heating of the lower photosphere. This is further supported by a rough hydromechanical model of an acoustic transient driven by sudden heating of the low photosphere. Where direct heating of the low photosphere by protons or high-energy electrons is unrealistic, the strong association between the acoustic source and co-spatial continuum emission can be regarded as evidence supporting the back-warming hypothesis, in which the low photosphere is heated by radiation from the overlying chromosphere. This is to say that a seismic source coincident with strong, sudden radiative emission in the visible continuum spectrum indicates a photosphere sufficiently heated so as to contribute significantly to the continuum emission observed.  相似文献   

2.
Ambastha  Ashok  Basu  Sarbani  Antia  H.M. 《Solar physics》2003,218(1-2):151-172
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.
The spectra of two powerful flares with approximately the same intensities in the optical region but with different spectral features and power in other regions are studied. One of them is the unique flare which occurred on October 28, 2003, importance X17.2/4B, ranking third in magnitude among the recorded flares. Another occurred on September 1, 1990, 3B importance. The flares vary in the Balmer decrement. The flare of October 28, 2003, has a ratio of I(Hβ)/I(Hα) = 1.47. This is the largest value for solar flares ever observed. The flares also differ in magnitude of the D Na I lines emission: the emission of the flare of October 28, 2003, is substantially larger than that of the other flare. The chromosphere models of the flares are computed using the observed profiles of Balmer lines and D Na I lines. The satisfactory agreement of the calculated and observed profiles is obtained for the two-component models in which a hot component occupies 6% of the area. The hot component of the chromosphere model is characterized with the dense condensation available in the upper layers. For the flare of October 28, 2003, this condensation is located deeper and its substance concentration is greater than that for another flare. The Hα line intensity for the model hot component alone is approximately 30 and the continuous spectrum intensity is approximately 3% of the undisturbed level. The photosphere model is computed using the observed profiles of photosphere lines for the flare of October 28, 2003. It is found that very broad profiles of individual sigma-components of the Fe I λ 525.0 nm line may be only explained by the presence of magnetic fields having different directions. A great difference is detected between values of the magnetic field strength obtained in the splitting of sigma-components and those provided by simulation.  相似文献   

4.
E. L. Chupp 《Solar physics》1988,118(1-2):137-154
We review the current observational knowledge on the production of neutrons in association with solar flares. From a study of the observations it is shown that unique information can be obtained on the spectral properties of accelerated ions produced during the flare. Also, the abundance of 3He/H in the photosphere can be directly determined. We also review the current interpretations of all available neutron observations and in particular highlight the uncertainties, and provide guide posts for future experiments.  相似文献   

5.
Solar circumstances have been evaluated for January 28, 1967, the date of an observed ground level enhancement of cosmic rays which was not preceded by observation of a suitably great Hα flare. On the visible solar hemisphere, a bright subflare at S23° E19° occurred in appropriate time association with the cosmic ray event, and was accompanied by weak X-ray enhancement and radio frequency emission. If this flare, alone, or in combination with other minor flares observed on the visible hemisphere on January 28 was the source of the energetic cosmic rays recorded on that date, then current thinking regarding the characteristics of cosmic ray flares must be modified. An initial study of probable circumstances on the invisible hemisphere did not lead to the immediate recognition of amajor center of activity as the probable source of a cosmic ray flare. Further evaluation of all centers of activity on the invisible hemisphere identified one region, McMath Plage No. 8687, 64° beyond the west limb, as the most plausible, possible site for the cosmic ray flare on January 28, 1967. The location of this region is in accord with the source-position deduced in Lockwood's analysis (1968) of the cosmic ray event. This center of activity could not have been more than 5 days old on January 28, 1967. The interval of major activity in the region was confined primarily to the invisible hemisphere. The occurrence of an ‘isolated’ major flare in the region on February 13, 1967 is discussed. The present study exemplifies the partial nature of solar observations which are limited to the visible hemisphere. The possible role of exceptional geomagnetic calm, 1963–1967, in permitting atypical cosmic ray enhancements, as on January 28, 1967, is mentioned.  相似文献   

6.
本文简要回顾了耀斑中正负电子湮灭线的形成过程,着重研究了一个强γ射线耀斑０ ．５１１ ＭｅＶ 线随时间的演化。结果表明,为解释观测数据,加速质子谱必须随时间变化, 从而间接地提出了一种基于０ ．５１１ ＭｅＶ 线获取加速质子谱演化信息的新途径。  相似文献   

7.
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   

8.
It has previously been suggested that the very high relative abundances of helium occasionally observed in the solar wind mark the plasma accelerated by major solar flares. To confirm this hypothesis, we have studied the 43 spectra with He/H 15% that were observed among 10300 spectra collected by Vela 3 between July 1965–July 1967. The 43 spectra were distributed among 16 distinct periods of helium enhancement, 12 of which (containing 75% of the spectra) were associated with solar flares. Six new flare-enhancement events are discussed in this paper. It is concluded that the association of helium enhancements with major flares is real, non-random and very strong.With this study, there are 12 cases of reliable associations between helium enhancements (He/H 15%) and flares reported in the literature. The general characteristics of these events are discussed. It is found that the flares are typically large and bright (2B or 3B), often they produce cosmic ray protons, and they are widely distributed in solar longitude. The average transit velocity of the pistons (i.e., flare accelerated driver gas) is in excellent agreement with earlier observations of flare shock velocities. The degree to which the pistons have been slowed in transit is in good agreement with theory. The average percentage of helium in the enhanced regions is 15%, but this number should not be considered more than an extremely rough estimate because of very arbitrary decisions that had to be made as to when we would consider an enhancement had ended. The number of positively charged particles in the enhanced region is estimated to be of the order of 4 × 1039.A qualitative discussion of some of the possibilities for the source of helium enhanced plasma is presented. It is suggested that the helium enriched plasma may be the piston producing the shock causing the Type II radio emission. The size of the Type II emission region and the number of particles in the helium enhancement permit an estimate to be made of the density of the corona at the origin of the piston. From this it is estimated further that the piston must come from below about 0.5 R , in agreement with the 0.2–0.3 R often given for the initial height of the Type II emission source. Recent theoretical discussions have indicated that the corona as a whole can be expected to show helium enrichments at these levels.It is pointed out that observations of solar wind helium enhancement can be expected to be a useful tool in studying the distribution and relative abundance of helium in different layers of the solar corona, as well as mechanisms for the acceleration of plasma by solar flares.  相似文献   

9.
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   

10.
C. Lindsey  A.-C. Donea 《Solar physics》2008,251(1-2):627-639
Instances of seismic transients emitted into the solar interior in the impulsive phases of some solar flares offer a promising diagnostic tool, both for understanding the physics of solar flares and for the general development of local helioseismology. Among the prospective contributors to flare acoustic emission that have been considered are: i) chromospheric shocks propelled by pressure transients caused by impulsive thick-target heating of the upper and middle chromosphere by high-energy particles, ii) heating of the photosphere by continuum radiation from the chromosphere or possibly by high-energy protons, and iii) magnetic-force transients caused by magnetic reconnection. Hydrodynamic modeling of chromospheric shocks suggests that radiative losses deplete all but a small fraction of the energy initially deposited into them before they penetrate the photosphere. Comparisons between the spatial distribution of acoustic sources, derived from seismic holography of the surface signatures of flare acoustic emission, and the spatial distributions of sudden changes both in visible-light emission and in magnetic signatures offer a possible means of discriminating between contributions to flare acoustic emission from photospheric heating and magnetic-force transients. In this study we develop and test a means for estimating the seismic intensity and spatial distribution of flare acoustic emission from photospheric heating associated with visible-light emission and compare this with the helioseismic signatures of seismic emission. Similar techniques are applicable to transient magnetic signatures.  相似文献   

11.
Lockwood  J.A.  Debrunner  H.  Flueckiger  E.O.  Ryan  J.M. 《Solar physics》2002,208(1):113-140
We have deduced the power-law rigidity spectra, J(P)=AP –, and the spectral evolution of the solar flare events that occurred in the present solar activity cycle on 6 November 1997, 14 July 2000, and 15 and 18 April 2001. The implications of these results for the acceleration of high-energy protons are discussed. The analysis is based on the ratios of the Mt. Washington to the Durham neutron monitor count-rate increases during the solar flare events. These two neutron monitors are located at different elevations (828 and 1030 g cm–2, respectively) but at approximately the same geographical latitude and longitude. The proton spectra from 1 to 10 GV determined from the ratios of the count rate increases of the two neutron monitors are found to agree with those deduced from the global neutron monitor network or selected neutron monitors in 10 solar flare events from 1960 to 1990 for which comparative results are available. Thus the ratio method is quick, easy and reliable for deducing the spectral shape of solar flare protons at neutron monitor rigidities and for obtaining the spectral evolution as a function of time.  相似文献   

12.
A solar flare with both H and Fe i 5324 emissions was observed in AR 7529 (S13, E65) on 24 June, 1993 at the Bejing Astronomical Observatory. Our calculations show that the Fe i 5324 emission region of the flare was located in the low photosphere at a height of about 180 km above 5000 = 1, which is lower than many previous studies of white-light flares. To study a Fe i 5324 flare, which represents a kind of extreme case in solar flares, would be useful for clarifying some arguments in the researches of white-light flares as well as for understanding the mechanism of solar flares.The synthetic analyses from vairous features of the flare lead to the following possible exciting mechanism of the Fe i 5324 flare: owing to the flow of energetic electrons from the corona and probably also the thermal conduction downward into the lower atmosphere, a condensation with a temperature higher than that below it was formed near the transition region. Then the low photosphere was heated through backwarming. The Fe i 5324 flare occurred as an indicator of the excitation in the low photosphere.  相似文献   

13.
D. J. Mullan 《Solar physics》1977,54(1):183-206
Short-lived increases in the brightness of many red dwarfs have been observed for the last 30 yr, and a variety of more or less exotic models have been proposed to account for such flares. Information about flares in the Sun has progressed greatly in recent years as a result of spacecraft experiments, and properties of coronal flare plasma are becoming increasingly better known. In this paper, after briefly reviewing optical, radio and X-ray observations of stellar flares, we show how a simplified model which describes conductive plus radiative cooling of the coronal flare plasma in solar flares has been modified to apply to optical and X-ray stellar flare phenomena. This model reproduces many characteristic features of stellar flares, including the mean UBV colors of flare light, the direction of flare decay in the two-color diagram, precursors, Stillstands, secondary maxima, lack of sensitivity of flare color to flare amplitude, low flux of flare X-rays, distinction between so-called spike flares and slow flares, Balmer jumps of as much as 6–8, and emission line redshifts up to 3000 km s–1. In all probability, therefore, stellar flares involve physical processes which are no more exotic (and no less!) than those in solar flares. Advantages of observing stellar flares include the possibilities of (i) applying optical diagnostics to coronal flare plasma, whereas this is almost impossible in the Sun, and (ii) testing solar flare models in environments which are not generally accessible in the solar atmosphere.  相似文献   

14.
We searched for solar neutrons using the data collected by six detectors from the International Network of Solar Neutron Telescopes and one Neutron Monitor between January 2010 and December 2014. We considered the peak time of the X-ray intensity of thirty five ≥ X1.0 class flares detected by GOES satellite as the most probable production time of solar neutrons. We prepared a light-curve of the solar neutron telescopes and the neutron monitor for each flare, spanning ± 3 h from the peak time of GOES. Based on these light curves, we performed a statistical analysis for each flare. Setting a significance level at greater than 3σ, we report that no statistically significant signals due to solar neutrons were found. Therefore, upper limits are determined by the background level and solar angle of these thirty five solar flares. Our calculation assumed a power-law neutron energy spectrum and an impulsive emission profile at the Sun. The estimated upper limits of the neutron emission are consistent within the order of magnitude of the successful detections of solar neutrons made in solar cycle 23.  相似文献   

15.
We compute the change in the Lorentz force integrated over the outer solar atmosphere implied by observed changes in vector magnetograms that occur during large, eruptive solar flares. This force perturbation should be balanced by an equal and opposite force perturbation acting on the solar photosphere and solar interior. The resulting expression for the estimated force change in the solar interior generalizes the earlier expression presented by Hudson, Fisher, and Welsch (Astron. Soc. Pac. CS-383, 221, 2008), providing horizontal as well as vertical force components, and provides a more accurate result for the vertical component of the perturbed force. We show that magnetic eruptions should result in the magnetic field at the photosphere becoming more horizontal, and hence should result in a downward (toward the solar interior) force change acting on the photosphere and solar interior, as recently argued from an analysis of magnetogram data by Wang and Liu (Astrophys. J. Lett. 716, L195, 2010). We suggest the existence of an observational relationship between the force change computed from changes in the vector magnetograms, the outward momentum carried by the ejecta from the flare, and the properties of the helioseismic disturbance driven by the downward force change. We use the impulse driven by the Lorentz-force change in the outer solar atmosphere to derive an upper limit to the mass of erupting plasma that can escape from the Sun. Finally, we compare the expected Lorentz-force change at the photosphere with simple estimates from flare-driven gasdynamic disturbances and from an estimate of the perturbed pressure from radiative backwarming of the photosphere in flaring conditions.  相似文献   

16.
This paper investigates the physical state of the photosphere in the main phase of the two-ribbon solar flare on June 3, 1979. The derived models show that the photosphere was in a disturbed state for a long time during the main phase of the flare. In the models, the temperature in the upper photospheric layers is higher and that in the lower layers is lower than in the quiet-sun model atmosphere. During the flare, the heating extends to the lower photospheric layers, and the upper layers cool down. A comparison of the obtained models to those for the two-ribbon solar flare on October 7, 1979, shows that the height distributions of the temperature in the main phase of the flares are strongly different.  相似文献   

17.
An M4.1/1B solar flare on November 5, 2004, is investigated. The Stokes I ± V profiles of nine photospheric Fe I, Fe II, Sc II, and Cr II lines are studied for three instants of this flare (11 h 35 m , 11 h 39 m , and 11 h 45 m UT). The magnetic fields in the flare were measured in two ways: using the center-of-gravity method and by comparing the observed profiles with the theoretical ones computed with Baranovsky’s code. Analysis of the profiles reveals that the magnetic field strength peaked in the upper photosphere (logτ500 = ?2.7) at the flare maximum (11 h 35 m ); this peak was smeared and shifted into the deeper photospheric layers as the flare evolved. The semiempirical model of the flare has two layers with an enhanced temperature: in the upper and middle photosphere. These layers also shifted deep into the photosphere as the flare evolved. The turbulent velocities at the distribution maximum increased by almost a factor of 5 compared to those in the undisturbed photosphere, while the plasma density both increased and decreased by a factor of 3–6.  相似文献   

18.
Quasi-separatrix layer, also called as QSL, is a region where magnetic connectivity changes drastically, and mostly well coincides with the location of flare ribbons in observations. The research on the relations of this topological structure with the 3-dimensional magnetic reconnection, and solar flares has attracted more and more attention. In this paper, using the theory of QSL we investigate a C5.7 classical two-ribbon solar flare (event 1) which occurred at AR11384 on 2011 December 26, and an M6.5 solar flare (event 2) which occurred at AR12371 on 2015 June 22, respectively. Combining the multi-wavelength data of AIA (Atmospheric Imaging Assembly) and vector magnetogrames of HMI (Helioseismic and Magnetic Imager) onboard SDO (Solar Dynamics Observatory), we extrapolate the coronal magnetic field using the PF (Potential Field) and NLFFF (Nonlinear Force Free Field) models, and calculate the evolution of the AR (Active Region) magnetic free energy. Then, we calculate the logarithmic distribution of Q-factors (magnetic squashing factor) at different heights above the solar photosphere with the results of the PF and NLFFF extrapolations, in order to determine the location of QSL. Afterward, we investigate the evolutionary relation between the QSLs at different heights above the solar photosphere and the flare ribbons observed at the corresponding heights. Finally, we study the multi-wavelength evolution features of the 2 flare events, and obtain by calculation the mean slip velocities of magnetic lines in the event 2 at 304 Å and 335 Å to be 4.6 km s-1 and 6.3 km s-1, respectively. We find that the calculated location of QSL in the chromosphere and corona is in good agreement with the location of flare ribbons at the same height, and the QSLs at different heights have almost the same evolutionary behavior in time as the flare ribbons of the corresponding heights, which highlights the role of QSL in the research of 3D magnetic reconnection and solar flare, and we suggest that the energy release in the flare of event 2 may be triggered by the magnetic reconnection at the place of QSL. We also suggest that the QSL is very important for us to study the essential relation between the 3D and 2D magnetic reconnections.  相似文献   

19.
Energetic proton measurements obtained from the GOES and IMP-8 satellites as well as from ground-based neutron monitors are compared with the GOES soft X-ray measurements of the associated solar flares for the period 1975–2003. The present study investigates a broad range of phenomenology relating proton events to flares (with some references to related interplanetary disturbances), including correlations of occurrence, intensities, durations and timing of both the particle event and the flare as well as the role of the heliographic location of the designated active region. 1144 proton events of > 10 MeV energy were selected from this 28-year period. Owing primarily to the low particle flux threshold employed more than half of this number was found to be reliably connected with an X-ray flare. The statistical analysis indicates that the probability and magnitude of the near-Earth proton enhancement depends critically on the flare's importance and its heliolongitude. In this study all flares of X-ray importance > X5 and located in the most propitious heliolongitude range, 15∘W to 75∘W, were succeeded by a detectable proton enhancement. It was also found that the heliolongitude frequently determines the character of the proton event time profile. In addition to intensity, duration and timing, proton events were found to be related to the other flare properties such as lower temperatures and longer loop lengths.  相似文献   

20.
Soft solar X-rays (8 gl 12 Å) were observed from OSO-III. An analysis of the X-ray enhancements associated with 165 solar flares revealed that there is a tendency for a weak soft X-ray enhancement to precede the cm- burst and H flare. The peak soft X-ray flux follows the cm- peak by about 4 min, on the average. Additionally, it was found that flare-rich active centers tend to produce flares which are stronger X-ray and cm- emitters than are flares which take place in flare-poor active centers.  相似文献   

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