共查询到20条相似文献，搜索用时 15 毫秒
1.
The active region NOAA 6555 had several locations of highly sheared magnetic field structure, yet, only one of them was the site for all the five X-class flares during its disk passage in March 1991. The pre-flare observations of high-resolution H filtergrams, vector magnetograms and H Dopplergrams of the 2B/X5.3 flare on 25 March 1991 show that the flaring site was characterized by a new rising emerging flux region (EFR) near the highly sheared magnetic field configuration. The polarity axis of the emerging flux was nearly perpendicular to the pre-existing magnetic neutral line. The location of the EFR was the site of initial brightening in H. The post-flare magnetograms show higher magnetic shear at the flare location compared to the post-flare magnetograms, which might indicate that the EFR was sheared at the time of its emergence. As the new EFR coincided with the occurrence of the flare, we suggest that it might have triggered the observed flare. Observations from Big Bear Solar Observatory and Marshall Space Flight Center also show that there was emergence of new flux at the same location prior to two other X-class flares. We find that out of five observed X-class flares in NOAA 6555, at least in three cases there are clear signatures of flare-related flux emergence. Therefore, it is concluded that EFRs might play an important role in destabilizing the observed sheared magnetic structures leading to large X-class flares of NOAA 6555. 相似文献
2.
We analyzed simultaneous EUV images from the Transition Region And Coronal Explorer (TRACE) and H and H filtergrams from Huairou Solar Observing Station (HSOS). In active region NOAA 8307, an H C5.5 flare occurred near 06:10 UT on 23 August 1998. In this paper, we concentrated on loop–loop interaction, as well as their relationship to the C5.5 flare. We find that while opposite polarity magnetic fields cancelled each other, H bright points appeared, and then the flare occurred. Looking at EUV images, we noticed that a TRACE flare, associated with the C5.5 flare in H and H filtergrams, first appeared as patch-shaped structures, then the flare patches expanded to form bright loops. We used a new numerical technique to extrapolate the chromospheric and coronal magnetic field. Magnetic field loops, which linked flare ribbons, were found. It was suggested that loop interaction in the active region was the cause of the TRACE and H flare; the magnetic topological structures were clearly demonstrated and the TRACE flare was probably due to the interaction among energetic low-lying and other longer (higher) magnetic loops. Each primary flare kernel, seen from H, H filtergrams, and EUV images, was located near the footpoints of several interacting loops. 相似文献
3.
Edward N. Frazier 《Solar physics》1972,24(1):98-112
High resolution photographic magnetograms are compared with H filtergrams (both on- and off - band) for a wide variety of solar features. It is verified that H filaments overlie neutral lines or bands and that H plages always occur at magnetic field clumps. However, the brightness of H plages bear no relation to magnetic field strength or polarity, and the direction of the magnetic field with respect to threads and filaments remains obscure. Counter-examples can be found for virtually every rule that has been formulated so far.Basic questions about the usefulness and final research goal of filtergrams and magnetograms are raised. It is shown that neither filtergram or magnetogram alone is capable of furnishing a unique solution. It is suggested that the proper direction for research is to use magnetograms, together with (as yet unspecified) additional sources of data, to understand H structures. 相似文献
4.
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
5.
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
6.
A detailed study of the evolution and cooling process of post-flare loops is presented for a large X9.2 solar flare of 2 November 1992 by using H images obtained with Domeless Solar Telescope at Hida Observatory and soft X-ray images of Yohkoh Soft X-ray Telescope (SXT). The detailed analysis with a new method allows us to determine more precise values of the cooling times from 107 K to 104 K plasma in the post-flare loops than in previous works. The subtraction of sequential images shows that soft X-ray dimming regions are well correlated to the H brightening loop structure. The cooling times between 107 K and 104 K are defined as the time difference between the start of soft X-ray intensity decrease and the end of H intensity increase at a selected point, where the causal relation between H brightening and soft X-ray dimming loops is confirmed. The obtained cooling times change with time; about 10 min at the initial stage and about 40 min at the later stage. The combined conductive and radiative cooling times are also calculated by using the temperature and density obtained from SXT data. Calculated cooling times are close to observed cooling times at the beginning of the flare and longer in the later stage. 相似文献
7.
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
8.
We obtained a complete set of H, Ca 8542 and He I 10830 spectra and slit-jaw H images of the C5.6 limb flare of 1 August 2003 using the Multi-channel Infrared Solar Spectrograph (MISS) at Purple Mountain Observatory. This flare was also observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and partially by the Extreme-ultraviolet Imaging Telescope (EIT) on SOHO. This flare underwent a rapid rising and expanding episode in the impulsive phase. All the H, Ca 8542 and He I 10830 profiles of the flare are rather wide and the widest profiles were observed in the middle bright part of the flare instead of at the flare loop top near the flare maximum. The flare manifested obvious rotation in the flare loop and the decrease of the rotation angular speed with time at the loop-top may imply a de-twisting process of the magnetic field. The significant increases of the Doppler widths of these lines in the impulsive phase reflect quick heating of the chromosphere, and rapid rising and expanding of the flare loop. The RHESSI observations give a thermal energy spectrum for this flare, and two thermal sources and no non-thermal source are found in the reconstructed RHESSI images. This presumably indicates that the energy transfer in this flare is mainly by heat conduction. The stronger thermal source is located near the solar limb with its position unchanged in the flare process and spatially coincident with the intense EUV and H emissions. The weaker one moved during the flare process and is located in the H dark cavities. This flare may support the theory of the magnetic reconnections in the lower solar atmosphere. 相似文献
9.
We study the active region NOAA 6718 and the development of a (2N, M3.6) flare in radio and H. Due to our knowledge of the magnetic field structure in the active region we are able to associate the different radio flare burst components with the stages in the H flare evolution. A discussion of the data in terms of chromospheric flare kernel heating reveals that in the present case the observed flare-related radio burst continuum switch-off is caused by the penetration of hot, ablated gas into the coronal radio source. 相似文献
10.
Marie K. McCabe 《Solar physics》1985,98(1):127-140
The H observations of a limb flare, which were associated with exceptional gamma-ray and hard X-ray emission, are presented and discussed. The good spatial and temporal resolution of the H data allow us to investigate the detailed structure of the elevated flare loops and the intensity variations of the loops, footpoints and surrounding chromosphere during each phase of the flare event. A delay time of 12 s was found between at least one of the hard X-ray (28–485 keV) peaks and corresponding H intensity maximum at a loop footpoint. A comparison is made between this event and another well-observed limb flare with many similar characteristics to seek evidence for the large difference in their levels of energy release. 相似文献
11.
Very faint H emission in the solar corona registered on over-exposed photographs made by a coronagraph and an H filter is studied. The over-exposed filtergrams have been processed by a Joyce Loebl automated microdensitometer and the two-dimensional scans have been analysed by the residual image method. A classification of the faint H emission objects, revealed on the isodensity maps, is proposed and the latitudinal distribution, the morphology, and the location with respect to the other active phenomena are analysed. Taking into account some possible plasma effects that could be caused by coronal magnetic field changes, a hydromagnetic interpretation of the faint H emission is proposed. 相似文献
12.
Yoshinori Suematsu Sumisaburo Saito Yasuhiro Funakoshi Hiroki Kurokawa 《Solar physics》1988,116(2):285-290
A coronal condensation was observed simultaneously with Fexiv 5303, Fex 6374, Fe xi 7892, and H filtergraphs. The size and shape of the condensation in 5303 are different from those in other filtergrams. H filtergrams taken around the eclipse time show that a small transient prominence exists in close proximity to the condensation core and behaves like a post-flare loop system, though the appearance is quite different and no flare-report exists. A small-scale energetic phenomenon seems to have occurred at the top of magnetic loops.Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 285. 相似文献
13.
K. A. Marsh 《Solar physics》1978,59(1):105-113
The flare-like events which are frequently seen in H in apparently quiet regions of the solar disk can in all cases be identified with bipolar features (ephemeral regions, ER) on magnetograms. These events represent the H counterpart of X-ray bright point flares.Statistically, this phenomenon is associated with the proximity of the bipolar features to the super-granulation network, in the sense that an ER is likely to flare during its lifetime if the distance to the nearest network element is less than or equal to its own pole separation. This conclusion is supported by direct study of time sequences of magnetograms and H pictures, which manifest the interaction of ER with the supergranulation network. The flare-like brightenings in some examples occurred in the region of interaction between network flux and one pole of the ER.The consequence of this interaction is that small quantities of network flux are transported over distances of the order of the ER pole separations. This may have an important effect on the long-term diffusion of magnetic flux. 相似文献
14.
M. Dizer 《Solar physics》1969,10(2):416-428
We report measurements made on the brightness in H of all parts of the flare photographed through a birefringent filter centered on H, using a scanning isodensitometer. From obtained isophotes of the flares we derived some information on the morphological changes in the flare and estimated the total energy in H of the flare. 相似文献
15.
One hundred seventy-eight Ellerman bombs were identified and studied with on- and off-band H filtergrams of two active centers, one near disk center and the other near the east limb. The photographs, taken through a 1/4 Å bandpass filter, occasionally attained resolution as fine as 0.3. The mean duration of bombs at H-2 Å was about 13 min near disk center and 11 min near the limb; these times increase slightly when we observe closer to the core of H. Eighty-six percent of the bombs in the near-limb region and 56% in the disk-center region were seen to be accompanied by ejections of dark material; the ejections were 3–30 long. The ejection length appears to be proportional to the bomb size times the bomb lifetime. 相似文献
16.
Warmuth Alexander Hanslmeier Arnold Messerotti Mauro Cacciani Alessandro Moretti Pier Francesco Otruba Wolfgang 《Solar physics》2000,194(1):103-120
NOAA 8210 has been a region showing a remarkable level of activity well before solar maximum. Dominated by a large, rapidly rotating spot, it produced several intense flares during its disk passage at the end of April–beginning of May 1998. We examine the development of AR 8210 in H and white light (WL) and study the evolution of its complex magnetic topology. While the other principal flares are briefly reviewed, the great X1.1/3B flare of 2 May, which was observed at Kanzelhöhe Solar Observatory during a SOHO/UVCS ground support campaign, is studied in detail. This event has been documented in full-disk H and Na-D intensitygrams, Dopplergrams, and magnetograms, with a time cadence of one minute each. The flare was associated with a CME and produced significant geomagnetic effects. Furthermore, we point out the perspectives for our planned Flare Monitoring and Alerting System, since the two new instruments (Magneto-Optical Filter and Digital H camera), which made their first operational run with the campaign, are crucial components for this program. 相似文献
17.
A limb, two-ribbon H flare on June 4, 1991, associated with a white-light flare and followed by an emission spray and post-flare loops, is studied. A region of rapidly enhanced brightness at the bottom of the H ribbon above the white-light flare is revealed. The energy released by the white-light flare at eff = 4100 is estimated to be about 1.5 × 1028 erg s–1. 相似文献
18.
H. Zirin 《Solar physics》1978,58(1):95-120
I have studied a number of flares for which good X-ray and optical data were available. An average lag of 5.5 s between hard X-ray (HXR) start and H start, and HXR peak and Ha peak was found for 41 flares for which determination was possible. Allowing for time constants the time lag is zero. The peak H lasts until 5–6 keV soft X-ray (SXR) peak. The level of H intensity is determined by the SXR flux.Multiple spikes in HXR appear to correspond to different occurrences in the flare development. Flares with HXR always have a fast H rise. Several flares were observed in the 3835 band; such emission appears when the 5.1–6.6 keV flux exceeds 5 × 104 ph cm-2 s-1 at the Earth. Smaller flares produce no 3835 emission; we conclude that coronal back conduction cannot produce the bright chromospheric network of that wavelength.The nearly simultaneous growth of H emission at distant points means an agent travelling faster than 5 × 103 km s-1 is responsible, presumably electrons.In all cases near the limb an elevated Ha source is seen with the same time duration as HXR flux; it is concluded that this H source is almost always an elevated cloud which is excited by the fast electrons. A rough calculation is given. Another calculation of H emission from compressed coronal material shows it to be inadequate.In several cases homologous flares occur within hours with the same X-ray properties.Radio models fit, more or less, with field strengths on the order of 100G. A number of flares are discussed in detail. 相似文献
19.
Based on the photospheric vector magnetograms taken at Huairou Solar Observing Station (HSOS), H images taken at Hiraiso Solar Terrestrial Research Center of Communication Research Laboratory, soft X-ray images taken by Yohkoh and an extrapolation method, the magnetic field structures and some active phenomena of the active region AR 7321 around 04:12 UT on 27 October 1992 are analyzed in this paper. A divergence of the transverse magnetic field, located at a newly formed spot, was found. At least four highly sheared magnetic field systems separately spread from this divergence to four other sites around this divergence. Vertical current concentrations are upward in this region and downward in the other four sites, and the corresponding H bright patches and soft X-ray bright loops coincide with these structures, confirming the existence of these four systems. The extrapolated magnetic force lines reconstructed by the Boundary Element Method (BEM), force-free field assumption, and boundary condition of observed photospheric vector magnetic field, coincide in space with the H bright patches and soft X-ray bright loops, showing that this extrapolation method is very effective and suggesting that the H bright patches and soft X-ray bright loops in this case represent the magnetic field structures in the upper atmosphere of the Sun.The bright structures in the H images and the soft X-ray images have a close correlation with the non-potential characteristics of the magnetic fields. 相似文献
20.
H observations, using the Multichannel Subtractive Double Pass (MSDP) spectrograph operating on the Meudon Solar Tower, have been made of an active region filament which undergoes a disparition brusque. The period of observation was from 10 45 to 13 30 UT on 22 June, 1981. Velocity and intensity fluctuations in H were measured. The proper motions of ejecta were followed allowing their trajectories and vector velocities to be determined. To model the dynamics of ejecta several models using thermal or magnetic driving forces are compared. The most promising model explains the motion as the consequence of magnetic stresses acting on an isolated magnetized plasmoïd in a diverging flux tube. 相似文献