共查询到20条相似文献，搜索用时 31 毫秒
1.
A recurrent H surge was observed on 7 October, 1991 on the western solar limb with the Meudon MSDP spectrograph. The GOES satellite recorded X-ray subflares coincident with all three events. During two of the surges high-resolutionYohkoh Soft X-ray Telescope (SXT) images have been taken. Low X-ray loops overlying the active region where the surges occurred were continuously restructuring. A flare loop appeared at the onset of each surge event and somewhat separated from the footpoint of the surge. The loops are interpreted as causally related to the surges. It is suggested that surges are due to magnetic reconnection between a twisted cool loop and open field lines. Cold plasma bubbles or jets squeezed among untwisting magnetic field lines could correspond to the surge material. No detection was made of either X-ray emission along the path of the surges or X-ray jets, possibly because of the finite detection threshold of theYohkoh SXT. 相似文献
2.
E. J. Schmahl 《Solar physics》1981,69(1):135-146
A search was made for EUV surges among the EUV flares recorded by the Harvard spectroheliometer on ATM. Out of a large set of partial observations of such flares, a subset of 24 complete events was chosen. More than 24 associated surges were found, many of them multiple events. The flare-surge correlation is therefore considerably higher in the EUV than in H, presumably because EUV surges generally appear in emission, and in high contrast compared to H. In over 70% of the cases, the surges were found to grow out of the flare structure. Making reasonable assumptions, it was possible to infer the magnitude of the gas pressure gradient from the flare core into the surge by using the EUV intensity gradient. The inferred pressure gradient appears sufficient to drive the surge, although higher resolution observations will be required to corroborate this, and rule out the importance of magnetic Lorentz force. 相似文献
3.
The evolution of coronal and chromospheric structures is examined together with magnetograms for the 1B flare of January 19, 1972. Soft X-ray and EUV studies are based on the OSO-7 data. The H filtergrams and magnetograms came from the Sacramento Peak Observatory. Theoretical force-free magnetic field configurations are compared with structures seen in the soft X-ray, EUV and H images. Until the flare, two prominent spots were connected by a continuous dark filament and their overlying coronal structure underwent an expansion at the sunspot separation rate of 0.1 km s–1. On January 19, the flare occurred as new magnetic fields emerged at 1019 Mx h–1 beneath the filament, which untwisted and erupted as the flare began. The pre-flare coronal emissions remained unchanged during the flare except for the temporary addition of a localized enhancement that started 5 min after flare onset. EUV lines normally emitted in the upper transition region displayed a sudden enhancement coinciding in time and location with a bright H point, which is believed to be near the flare trigger or onset point. The EUV flash and the initial H brightening, both of which occurred near the center of the activated filament, were followed by a second EUV enhancement at the end of the filament. The complete disruption of the filament was accompanied by a third EUV enhancement and a rapid rise in the soft X-ray emission spatially coincident with the disappearing filament. From the change of magnetic field inferred from H filtergrams and from force-free field calculations, the energy available for the flare is estimated at approximately 1031 erg. Apparently, changes in the overlying coronal magnetic field were not required to provide the flare energy. Rather, it is suggested that the flare actually started in the twisted filament where it was compressed by emerging fields. Clearly, the flare started below the corona, and it appears that it derived its energy from the magnetic fields in or near the filament.NCAR is sponsored by NSF. 相似文献
4.
A time series of K3 spectroheliograms taken at the Coimbra Observatory exhibits an erupting loop on the east limb on July 9, 1982 in active region NOAA 3804. The Goddard SMM Hard X-Ray Burst Spectrometer (HXRBS) observations taken during this period reveal a hard X-ray flare occurring just before the loop eruption is observed, and SMS-GOES soft X-ray observations reveal a strong long-duration event (LDE) following the impulsive phase of the flare. A Solwind coronagram exhibits a powerful coronal mass ejection (CME) associated with the erupting loop. H flare and prominence observations as well as centimeter and decimeter radio observations of the event are also reviewed. A large, north–south-oriented quiescent prominence reported within the upper part of the CME expansion region may play a role in the eruption as well. The spatial and temporal correlations among these observations are examined in the light of two different current models for prominence eruption and CME activation: (1) The CME is triggered by the observed hard X-ray impulsive flare. (2) The CME is not triggered by a flare, and the observed soft X-ray flare is an LDE due to reconnection within the CME bubble. It is concluded that this event is probably of a mixed type that combines characteristics of models (1) and (2). The July 9 event is then compared to three other energetic CME and flare eruptions associated with the same active-region complex, all occurring in the period July 9 through September 4, 1982. It is noted that these four energetic events coincide with the final evolutionary phase of a long-lasting active-region complex, which is discussed in a companion paper (Bumba, Garcia, and Jordan, 1997). The paper concludes by addressing the solar flare myth controversy in the light of this work. 相似文献
5.
MEIN P. MEIN N. MALHERBE J.-M. HEINZEL P. KNEER F. VON UEXKULL M. STAIGER J. 《Solar physics》1997,172(1-2):161-170
A small flare was observed at the Teide Observatory on October 5, 1994. Simultaneous data were obtained at the German Vacuum Tower Telescope (VTT) with the MSDP spectrograph providing high-resolution imaging spectroscopy in two chromospheric lines, and the Gregory Coudé Telescope (GCT) providing information about the magnetic field. Basic flare characteristics are:The area of the flare kernel ( 2 x 2 arc sec) is similar in H and Caii 8542 Å.The early phase of the flare is characterized by a blue asymmetry in H and a red one in Caii 8542 Å line.The evolutions of line profiles are different; the red asymmetry observed in the Caii line is detected a few seconds later in H.The maximum asymmetry of the Caii line does not coincide with the maximum brightness.The flare occurs in a region of a strong horizontal gradient of the line-of-sight component of the magnetic field.Brightness and asymmetry in H and Caii are discussed in the context of standard flare models and velocity fields. Our observations suggest that a magnetic reconnection could occur at low levels of the solar atmosphere. 相似文献
6.
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
7.
Shortly after the dynamic flare of 14 44 UT on 6 November, 1980, which initiated the second revival in the sequence of post-flare coronal arches of 6–7 November, a moving thermal disturbance was observed in the fine field of view of HXIS. From 15 40 UT until about 18 UT, when it left the field of view, the disturbance rose into the corona, as indicated by a projected velocity of 7.4 km s-1 in the south-east direction. The feature was located above the reconnection region of the dynamic flare and was apparently related to the revived coronal arch. Observations in the coarse field of view after 18 UT revealed a temperature maximum in the revived arch, rising with a velocity of 7.0 km s-1 directly in continuation of the thermal disturbance. The rise velocity of the disturbance was initially (at least until 17 20 UT) very similar to the rise velocities observed for the post-flare loop tops of the parent flare. This suggests that the rise of the reconnection point, in the Kopp and Pneuman (1976) mechanism responsible for the rise of the loop tops, also dictates the rise of the disturbance. From energy requirements it follows that in this phase the disturbed region is still a separate magnetic island, thermally isolated from the old arch structure and the post-flare loops. After 18 UT the rise of the post-flare loop tops slowed down to 2 km s-1, which is significantly slower than the rise of the brightness and temperature maxima of the revived arch in the coarse field of view. Thus in this phase the Kopp and Pneuman mechanism is no longer directly responsible for the rise of the thermal structure and the rise possibly reflects the merging of the old and the new arch structures.A similar thermal disturbance was observed after the dynamic flare of 07: 53 UT on 4 June, 1980. On the other hand, the confined flare of 17 25 UT on 6 November, 1980, did not show this phenomenon. Apparently this type of disturbance occurs after dynamic flares only, in particular when the flare is associated with an arch revival. 相似文献
8.
I. N. Garczyńska B. Rompolt A. O. Benz C. Slottje A. Tlamicha C. Zanelli 《Solar physics》1982,77(1-2):277-283
The 120 limb surges which have been observed by means of Wrocaw Observatory coronagraph from September 1966 to November 1977 are investigated. The evolution of surges was compared with the radio data during the surges. A correlation between radio bursts and the surges was found, particularly with chains of type I radio bursts, which is the first reliable correlation found of these bursts with non-radio events. The type I correlation only applied for surges without accompanying flare, of which 43% are correlated with this type of radio emission. In 23 of 30 associated events the start of a surge coincided within 5 minutes with the start or an enhancement of the type I storm. If flares were present, the association was not significant.We also compared the maximum height reached by a surge with the frequencies of the radio bursts emitted at the same time and the maximum velocity of the rising surge with the frequency drift of type I chains. No such a correlation was however found.We discuss the possibility that surges are the result of a sudden energy input into the chromosphere related to the type I source in the corona. 相似文献
9.
Richard A. Harrison 《Solar physics》1996,166(2):441-444
Recently Gosling (1993) examined the interplanetary consequences of solar activity, and suggested that the coronal mass ejection (CME) was the prime driver of most disturbances (i.e., interplanetary shocks, high-energy particles, geomagnetic storms, etc.) and that the solar flare was relatively unimportant in this context. He coined the phrase Solar Flare Myth. Since that paper there has been much debate on the origin of interplanetary disturbances - most people sitting squarely in the flare or CME camp. vestka (1995) has attacked Gosling's conclusions on the grounds that it is misleading to ignore the flare, and that past flare classifications were perfectly adequate for explaining the observations described by Gosling. This paper is a comment on vestka's report and an attempt to put the Solar Flare Myth into perspective - indeed it is an attempt to view the solar flare/CME phenomena in a more constructive light. 相似文献
10.
In this paper we study some absorbing features seldom associated with flare occurrence and observed in the wings of H by means of a cinematographic patrol.We describe short lived chromospheric dark features with strong velocity fields and we show their correlation with the birth and the further development of an active center.It is shown that radial velocities precede the modifications of magnetic fields.An attempt to compare these chromospheric velocities and photospheric ones points out that it could be possible to find good correlation between them in a changing but not flaring region. 相似文献
11.
V. V. Korneev V. V. Krutov S. L. Mandelstam A. M. Urnov I. A. Zhitnik E. Ya. Golts E. Ya. Kononov Y. V. Sidelnikov 《Solar physics》1979,63(2):319-327
Results are presented of an investigation of solar flare X-ray spectra in the region 1.70–1.95 Å, obtained aboard the Intercosmos-4 satellite during the maximum of solar activity (October–November, 1970). With the use of 6 high resolution spectra in the region 1.85–1.87 Å the identification of lines due to 18 transitions of 2p 1s type, consisting of the resonance, intercombination and forbidden Fe xxv ion lines and the satellite Fe xxiv lines has been performed. With the use of the recent laboratory data the averaged wavelengths of the lines were obtained confirming the theoretically calculated ones with an accuracy about ± 0.0004 Å. A variable Doppler shift of the Fe xxv resonance lines was observed for the flare of November 16, 1970, which points to hot plasma motions with velocities up to 400 km s-1. 相似文献
12.
The unique surge activity that occurred in McMath 9760 region during November 7 to November 16, 1968 is described and discussed. The surge activity was unusually intense; over 70 surges were observed, some of which were very highly energetic. Some surges were accompanied by surge brightenings; the latter caused a marked sharp increase in the velocity of the ejected matter. The region was studied at H -0.5 Å. In spite of the enhanced activity, the region appeared to be highly stable. 相似文献
13.
We obtained a set of well-observed 2D H spectral data of a 1N/M1.5 flare from the Solar Tower of Nanjing University. Using the H spectra, the sites of electron precipitation and high coronal pressure have been found, and the Doppler velocity was calculated from the red asymmetry of the H emission line by use of the bisector method. The current density distribution was also computed from magnetic field measurements. We have coaligned the H spectroheliograms and the magnetograms. It was found that the sites of electron precipitation were at the edge of a main current area. The sites of red asymmetry coincided with those of high coronal pressure. The flare reached its maximum in the magnetic shear region, though it began in a weak magnetic field. Several flare models are discussed to see which one could satisfy the observation. 相似文献
14.
The high-resolution H images observed during the decay phase of a long-duration flare on 23 March 1991 are used to study the three-dimensional magnetic field configuration of the active region NOAA 6555. Whereas all the large flares in NOAA 6555 occurred at the location of high magnetic shear and flux emergence, this long-duration flare was observed in the region of low magnetic shear at the photosphere. The H loops activity started soon after the maximum phase of the flare. There were a few long loop at the initial phase of the activity. Some of these were sheared in the chromosphere at an angle of about 45° to the east-west axis. Gradually, an increasing number of shorter loops, oriented along the east-west axis, started appearing. The chromospheric Dopplergrams show blue shifts at the end points of the loops. By using different magnetic field models, we have extrapolated the photospheric magnetograms to chromospheric heights. The magnetic field lines computed by using the potential field model correspond to most of the observed H loops. The height of the H loops were derived by comparing them with the computed field lines. From the temporal evolution of the H loop activity, we derive the negative rate of appearance of H features as a function of height. It is found that the field lines oriented along one of the neutral lines were sheared and low lying. The higher field lines were mostly potential. The paper also outlines a possible scenario for describing the post-flare stage of the observed long-duration flare. 相似文献
15.
On 11 January 2002, using the Multi-channel Infrared Solar Spectrograph (MISS) at the Purple Mountain Observatory (PMO), we obtained Hα, Ca ii 8542 Å and He i 10?830 Å spectra and slit-jaw Hα images of a peculiar solar limb event. A close resemblance of its intensity to that of a small flare and the GOES X-ray flux indicates that it was an active prominence. However, its morphological evolution and velocity variation were different from general typical active prominences, such as limb flares, post-flare loops, surges and sprays. It started with the ejection of material from the flare site. In the early phase, the ejecta was as bright as a limb flare and kept rising until reaching the height of (8????10)×104 km at an almost constant velocity of 91.7 km? s ?1 with its lower part always connected to the solar surface. EUV images in 195 Å show similar structure as in the Hα line, indicating the coexistence of plasmas with temperatures differing by more than two orders of magnitude. Later some material started to fall back to another bright area on the solar surface. The falling material did not show the collimated structure of surges or the arc structure of flaring arches. A red-shift velocity of more than 200 km? s ?1 was detected in a bright point close to the outer edge of the closed loop system formed later, which dispersed in a few minutes and became a part of the newly formed large loop. The ejected material did not leave the sun, indicating that the magnetic reconnection was not sufficient to remove the overlying field lines during the process. The spectral line profiles showed large widths and variable velocities, and therefore the line-pair method is not applicable to this event for the estimation of physical parameters. 相似文献
16.
David F. Webb 《Solar physics》1985,97(2):321-344
A comprehensive survey of Skylab S-054 soft X-ray images was performed to investigate the characteristics of coronal enhancements preceding solar flares. A search interval of 30 min before flare onset was used. A control sample was developed and tests of the statistical results performed. X-ray images with preflare enhancements were compared with high resolution H images and photospheric magnetograms.The results are as follows: preflare X-ray enhancements were found in a statistically significant number of the preflare intervals, and consisted of one to three loops, kernels or sinuous features per interval. Typically, the preflare feature was not at the flare site and did not reach flare brightness. There was no systematically observed time within the preflare interval for the preflare events to appear and no correlation of preflare event characteristics with the subsequent flare energy. Gas pressures of several preflare features were calculated to be on the order of several dyne cm–2, typical of active region loops, not flares. These results suggest that observations with both high spatial resolution and low coronal temperature sensitivity are required to detect these small, low pressure enhancements that preceded the smaller flares typical of the Skylab epoch. H brightenings were associated with nearly all of the preflare X-ray enhancements. Changing H absorption features in the form of surges or filament activations were observed in about half of the cases. These results do not provide observational support for models which involve preheating of the flare loop, but they are consistent with some current sheet models which invoke the brightening of structures displaced from the flare site tens of min before onset. 相似文献
17.
We compare large-scale filtergrams of a hitherto neglected class 1B flare with previously published vector magnetograms and maps of photospheric longitudinal electric current density (Hagyard et al., 1985). The vector magnetic fields were mapped simultaneously with the eruption of this flare. We find a coincidence, to within the ±2 registration accuracy of the data, between the flare kernels and the locations of maximum shear and of peak values in the longitudinal electric current density. The kernels brighten in a way which implies that the preflare heating and the main release of flare energy are spatially coincident within the limits of resolution (2). A pronounced magnetic shear exists in the vertical direction at the location of the strongest flare kernels. We provide evidence that the electric currents could be maintained by the energy stored in the sheared transverse magnetic field and that the amount of energy released is proportional to the amount stored. These circumstances are consistent with theories in which flares are triggered by plasma instabilities due to surplus electric currents. 相似文献
18.
Using photospheric and H observations and total radio flux data we study a two-ribbon flare in AR NOAA 4263 which was a part of a flare event complex on July 31, 1983. We find some facts which illuminate the special way of flare triggering in the analysed event. Around a double spot the photospheric vector magnetic field is discussed with respect to the chromospheric activities. In one of the spots the feet of long stretched loops are pushed down under steepening loops rooted in the same spot. This causes energy build-up by twist and shear in the stretched loops. One foot of the two-ribbon flare (triggered in the stretched and underpushed loop system) roots in a part of the spot umbra and penumbra where the field runs in extremely flat like a pressed spiral spring. A strange radio event, starting before the flares, can be interpreted as a precursor activity of the flare event complex. The radio data support the view that the analyzed flare process and the given magnetic field structure, respectively, are not very effective in energetic particle generation and escape. 相似文献
19.
On 27 September 1998, Big Bear Solar Observatory (BBSO) and Transition Region and Coronal Explorer (TRACE) coordinated observations from 16:00 to 19:00 UT to study properties of microflares in AR NOAA No. 8340. Fortuitously, a C5.2 flare occurred at 16:30 UT in this active region. H and magnetograph movies were obtained at BBSO; Civ 1550 Å, Feix 171 Å, and Fexii 195 Å movies were obtained by TRACE; both with a cadence about 1 min. In this paper, we concentrate on the study of magnetic properties of 70 Civ microflares, as well as their relationship to the C5.2 flare. We obtained the following results: (1) We found two kinds of microflares: microflares of transient brightenings with a time scale of 1 to 5 min (impulsive events) and microflares lasting half an hour or longer (persistent events). Ninety percent of the microflares are impulsive events. Most of the event in this category are associated with well defined magnetic neutral lines, but some are found in non-neutral line areas. All of seven persistent events are found at parasitic magnetic configurations with inclusions of small magnetic flux within dominant magnetic flux of opposite polarity. (2) More than a third of the impulsive microflares occurred near the C5.2 flare site indicating that a local instability is responsible for both the C5.2 flare and microflares. This indirectly supports the avalanche theory of flare energy release, which implies that a big flare may be spatially associated with many small flares. 相似文献
20.
Spectra of a 2B flare on 3 February, 1983 were observed simultaneously at H, H, and Can H, K lines with a multichannel spectrograph in the solar tower telescope of Nanjing University. The flare occurred in an extended region of penumbra at S 17 W07 from 05 : 41 to 07 : 00 UT. By use of an iterative method to solve the equations describing hydrostatic, radiative, and statistical equilibrium for hydrogen and ionized calcium atoms, five semi-empirical models corresponding to different times of the chromospheric flare have been computed. The results show that after the beginning of the flare, the heating of the chromosphere starts and the transition layer begins to be displaced downwards. However, during the impulsive phase the flare chromospheric region has a rapid outward expansion followed by a quick downward contraction. At the same time the transition layer starts to ascend and then descend again. After the H intensity maximum, the flare chromospheric region continues to condense and attains its most dense phase more than ten minutes after the maximum. Finally, the flare chromospheric region returns slowly to the normal chromospheric situation. 相似文献