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1.
We observed 4B/X17.2 flare in Hα from super-active region NOAA 10486 at ARIES, Nainital. This is one of the largest flares of current solar cycle 23, which occurred near the Sun’s center and produced extremely energetic emission almost at all wavelengths from γ-ray to radio-waves. The flare is associated with a bright/fast full-halo earth directed CME, strong type II, type III and type IV radio bursts, an intense proton event and GLE. This flare is well observed by SOHO, RHESSI and TRACE. Our Hα observations show the stretching/de-twisting and eruption of helically twisted S shaped (sigmoid) filament in the south-west direction of the active region with bright shock front followed by rapid increase in intensity and area of the gigantic flare. The flare shows almost similar evolution in Hα, EUV and UV. We measure the speed of Hα ribbon separation and the mean value is ∼ 70 km s-1. This is used together with photospheric magnetic field to infer a magnetic reconnection rate at three HXR sources at the flare maximum. In this paper, we also discuss the energetics of active region filament, flare and associated CME.  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.
From a 35-min time series of photographic spectra in the Caii H-line obtained at the Vacuum Tower Telescope (VTT) of the Sacramento Peak Observatory under high spatial, spectral, and temporal resolution, we have derived a large number of H-line profiles at the sites of the bright points in the interior of the supergranulation cells, and at the network elements, on a quiet region at the centre of the solar disc. It is shown that the bright points are associated with 3-min periodicity in their intensity oscillations whereas the network elements exhibit 7-min periodicity. It is surmised that the large difference in periods of the intensity oscillations, the strength of the magnetic fields, and the intensity enhancements at the sites of the bright points and the network elements themselves may probably be taken as evidence to argue that the mechanisms of heating in the two cases are dissimilar, irrespective of the sizes of these structures.  相似文献   

4.
We find that oscillations of the LOS velocity in Hα vary within facula regions. The power spectra show that the contributions of low-frequency modes (1.2 – 2 mHz) increase at the network boundaries. Three- and five-minute periods dominate inside cells. The spectra of photospheric and chromospheric LOS-velocity oscillations differ for most faculae. We detected several cases where oscillations in faculae seem to propagate horizontally with phase velocities of 50 – 70 km s−1. Their location in space and time coincided with the local maximum of the longitudinal magnetic field.  相似文献   

5.
R. Kariyappa 《Solar physics》1996,165(2):211-222
We have analysed a 35-min-long time sequence of spectra in the Caii H line, Nai D1 and D2 lines, and in a large number of strong and weak Fei lines taken over a quiet region at the center of the solar disk. The time series of these spectra have been observed simultaneously in these lines under high spatial, spectral, and temporal resolution at the Vacuum Tower Telescope (VTT) of the Sacramento Peak Observatory. We have derived the line profiles and their central intensity values at the sites of the chromospheric bright points, which are visible in the H line for easy identification. We have done a power spectrum analysis for all the lines, using their central intensity values to determine the period of oscillations. It is shown that the 3 Fei lines, present 23 Å away from the core of the H line representing the pure photospheric lines, Nai D1 and D2 lines, 6 Fei lines at the wings of H line, and Can H line exhibit 5-min, 4.05-min, 3.96-min, and 3.2-min periodicity in their intensity oscillations, respectively. Since all these lines form at different heights in the solar atmosphere from low photosphere to middle chromosphere and show different periodicities in their intensity oscillations, these studies may give an idea about the spatial and temporal relation between the photospheric and chromospheric intensities. Therefore these studies will help to better understand the physical mechanisms of solar oscillations. It is clearly seen that the period of intensity oscillations decreases outward from the low photosphere to the middle chromosphere. Since we have studied a single feature at a time on the Sun (i.e., bright points seen in the H line) in all these spectral lines simultaneously, this may explain about the footpoints of the bright points, the origin of 3-min oscillations, and the relation to other oscillations pertaining to these locations on the Sun. We have concluded that 80% of the bright points are associated with dark elements in the true continuum, and they may seem to have a relationship with the dark intergranular lanes of the photosphere, after carefully examining the brightness (bright threads) extending from the core to the far wings of the H line at the locations of a large number of bright points, using their time sequence of spectra.NRC Resident Research Associate, on leave from Indian Institute of Astrophysics, Bangalore 560034, India.  相似文献   

6.
We present a study of 10 microflares observed in 4–30 keV by SOXS mission simultaneously with Hα observations made at NAOJ, Japan during the interval between February and August 2004. The X-ray and Hα light curves showed that the lifetime of microflares varies between 4 and 25 min. We found that the X-ray emission in all microflares under study in the dynamic energy range of 4–30 keV can be fitted by thermal plus non-thermal components. The thermal spectrum appeared to start from almost 4 keV, low level discriminator (LLD) of both Si and CZT detectors, however it ends below 8 keV. We also observed the Fe line complex features at 6.7 keV in some microflares and attempted to fit this line by isothermal temperature assumption. The temperature of isothermal plasma of microflares varies in the range between 8.6 and 10.1 MK while emission measure between 0.5 and 2x1049 cm-3. Non-thermal (NT) emission appeared in the energy range 7–15 keV with exponent -6.8 ≤γ≤-4.8. Our study of microflares that had occurred on 25 February 2004 showed that sometimes a given active region produces recurrent microflare activity of a similar nature. We concluded from X-ray and simultaneous Hα observations that the microflares are perhaps the result of the interaction of low lying loops. It appears that the electrons that accelerated during reconnection heat the ambient coronal plasma as well as interact with material while moving down along the loops and thereby produce Hα bright kernels.  相似文献   

7.
We have used a high spatial and temporal resolution of long time sequence of spectra in CaII H-line obtained at the Vacuum Tower Telescope (VTT) of the Sacramento Peak Observatory on a quiet region at the center of the solar disk over a large number of bright points and network elements to search for atmospheric (chromospheric) g-mode oscillations. An important parameter of the H-line profile, intensity at H2v(Ih2V), has been derived from a large number of line profiles. We derived the light curves of all the bright points and network elements. The light curves represent the main pulse with large intensity amplitude and followed by several follower pulses with lower intensity amplitudes. The light curves of these bright points would give an impression that one can as well draw curves towards and away from the highest peak (main pulse) showing an exponential growth and decay of the amplitudes. An exponential decaying function has been fitted for all the light curves of the bright points to determine the damping time of the modes that are more or less the same, and one value of the coefficient of exponent can represent reasonably well the decay for all the cases. The FFT analysis of temporal variation of both the bright points and the network elements indicates around 10-min periodicity. We speculate that this longer period of oscillation may be related to chromospheric g-mode oscillations.  相似文献   

8.
Designing a statistical solar flare forecasting technique can benefit greatly from knowledge of the flare frequency of occurrence with respect to sunspot groups. This study analyzed sunspot groups and Hα and X-ray flares reported for the period 1997 – 2007. Annual catalogs were constructed, listing the days that numbered sunspot groups were observed (designated sunspot group-days, SSG-Ds) and for each day a record for each associated Hα flare of importance category one or greater and normal or bright brightness and for each X-ray flare of intensity C 5 or higher. The catalogs were then analyzed to produce frequency distributions of SSG-Ds by year, sunspot group class, likelihood of producing at least one flare overall and by sunspot group class, and frequency of occurrence of numbers of flares per day and flare intensity category. Only 3% of SSG-Ds produced a substantial Hα flare and 7% had a significant X-ray flare. We found that mature, complex sunspot groups were more likely than simple sunspot groups to produce a flare, but the latter were more prevalent than the former. More than half of the SSG-Ds with flares had a maximum intensity flare greater than the lowest category (C-class of intensity five and higher). The fact that certain sunspot group classes had flaring probabilities significantly higher than the combined probabilities of the intensity categories when all SSG-Ds were considered suggest that it might be best to first predict the flaring probability. For sunspot groups found likely to flare, a separate diagnosis of maximum flare intensity category appears feasible.  相似文献   

9.
We present and interpret observations of the preflare phase of the eruptive flare of 15 November, 1991 in NOAA AR 6919. New flux emerged in this region, indicated by arch filaments in Hα and increasing vertical flux in vector magnetograms. With increasing frequency before the eruption, transient dark Hα fibrils were observed that crossed Hα bright plage and the magnetic inversion line to extend from the region of flux emergence to the filament, whose eruption was associated with the flare. These crossing fibrils were dynamic, and were often associated with sites of propagating torsional motion. These sites propagated from the region of flux emergence into the filament flux system. We interpret these morphological and dynamic features in terms of relaxation after magnetic reconnection episodes which create longer field lines within the filament flux system, as envisioned in the tether cutting model, and transfer twist to it, as well. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005086108043  相似文献   

10.
Jain  Rajmal  Tripathy  S. C. 《Solar physics》1998,181(1):113-120
We report here the first direct evidence for detection of H intensity oscillations in two extended flares of 15 November 1989 and 20 April 1991. The relative intensity variations measured with time at 18 different flare and chromospheric locations were analysed to obtain the oscillation modes. The analysis shows prominent 5- and 3-min modes in flares in addition to their existence in the chromosphere. However, there exists a frequency difference between the flare and chromospheric modes. This frequency deviation of about 300 µHz is proposed as an influence of higher magnetic field, location of the measurements (height) in chromosphere, and high temperature in the flare.  相似文献   

11.
We report preliminary results of an observing run at the 1--m telescope at CTIO during which we followed RR Pic over several nights in February 2005. The resulting light curves show no sign of an eclipse. Apart from the 3.48 h period, which is usually interpreted as the orbital one, we find an additional period at P=3.78 h, which we interpret as the superhump period of the system.We furthermore present high–resolution Doppler maps in Hα, Hβ and He II, which we derived from observations at the NTT, La Silla in February 2004. They show strong variations in the emission distribution from one day to the next. While Hα and Hβ emission clearly show the accretion disc with some additional isolated sources, the He II emission is confined to an elongated region at low velocities.  相似文献   

12.
We present Hα observations from ARIES (Nainital) of a compact and impulsive solar flare that occurred on March 10, 2001 and which was associated with a CME. We have also analyzed HXT, SXT/Yohkoh observations as well as radio observations from the Nobeyama Radio Observatory to derive the energetics and dynamics of this impulsive flare. We coalign the Hα, SXR, HXR, MW, and magnetogram images within the instrumental spatial-resolution limit. We detect a single HXR source in this flare, which is found spatially associated with one of the Hα bright kernels. The unusual feature of HXR and Hα sources, observed for the first time, is the rotation during the impulsive phase in a clockwise direction. We propose that the rotation may be due to asymmetric progress of the magnetic reconnection site or may be due to the change of the peak point of the electric field. In MW emission we found two sources. The main source is at the main flare site and another is in the southwest direction. It appears that the remote source is formed by the impact of accelerated energetic electrons from the main flare site. From the spatial correlation of multiwavelength images of the different sources, we conclude that this flare has a three-legged structure.  相似文献   

13.
Ellerman bombs are bright emission features observed in the wings of Hα, usually in the vicinity of magnetic concentrations. Here we show that they can also be detected in the Ca II infrared triplet lines, which are easier to interpret and therefore allow for more detailed diagnostics. We present full Stokes observations of the 849.8 and 854.2 nm lines acquired with the new spectro-polarimeter SPINOR. The data show no significant linear polarization at the level of 3 × 10−4. The circular polarization profiles exhibit measureable signals with a very intricate pattern of peaks. A non-LTE analysis of the spectral profiles emerging from these features reveals the presence of strong downflows (∼10 {km s−1}) in a hot layer between the upper photosphere and the lower chromosphere. Visiting Astronomers, National Solar Observatory, operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under cooperative agreement with the National Science Foundation. The National Center for Atmospheric Research (NCAR) is sponsored by the National Science Foundation, USA.  相似文献   

14.
Results from a spectrophotometric study of the galaxy Kaz 701 are presented. Spectra of this galaxy were obtained on the 2.6-m telescope at the Byurakan Observatory with the SCORPIO spectral camera. In the spectra of Kaz 701, strong Hα, [OIII] λλ5007, 4959, and Hβ emission were observed, and the [SII]λλ6731, 6717 lines were observed with moderate intensities, while the [NII]λ6584 line was scarcely noticeable in the spectra obtained in 2004, but was much more intense in the spectra of 2009. The lines observed in the spectrum of this galaxy are typical of type Sy2 galaxies. A component was observed in the red wings of both the Hα and Hβ lines in the data of 2004, but, although these lines were stronger, these components were absent in the spectra taken in 2009. The relative intensities, equivalent widths, and half widths of these lines are given. These data, obtained in different observation periods (2004 and 2009), differ greatly; that is, the emission is variable.  相似文献   

15.
The use of integral characteristics of radio spots showed that in addition to the known 3–5-min oscillations, the above-spot regions of sunspots exhibit quasiperiodic oscillations of intensity, perimeter, sectional area, and area of the surface of the above-spot source radio image with periods in the ranges of 25–80, 90–110, 120–140, and 160–210 min. These periods are observed for all spots studied using the different characteristics of a radio source, which does not contradict the interpretation of these low-frequency oscillations as natural oscillations of spots near a certain position of stable equilibrium.  相似文献   

16.
Kosovichev  A.G.  Zharkova  V.V. 《Solar physics》1999,190(1-2):459-466
Using high-cadence magnetograms from the SOHO/MDI we have investigated variations of the photospheric magnetic field during solar flares and CMEs. In the case of a strong X-class flare of May 2, 1998, we have detected variations of magnetic field in a form of a rapidly propagating magnetic wave. During the impulsive phase of the flare we have observed a sudden decrease of the magnetic energy in the flare region. This provides direct evidence of magnetic energy release in solar flares. We discuss the physics of the magnetic field variations, and their relations to the Moreton Hα waves and the coronal waves observed by the EIT.  相似文献   

17.
Observations and analyses of two similar eruptive prominences on the north-east limb observed on 1980 April 27 at 0231 and 0517 UT, which are associated with the Boulder active region No. 2416 are presented. Both the eruptive prominences gave rise to white-light coronal transients as observed by C/P experiment of High Altitude Observatory on the Solar Maximum Mission. Type II and moving type IV radio bursts are reported in association with the first Hα eruptive prominence at 0231 UT. Both the Hα eruptive prominences showed pulse activity with a quasi-periodicity of about 2–4 min. We estimate a magnetic field in the eruptive prominence of about 100 G and a build-up rate ∼ 1026 ergs-1. The high build-up rate indicates that the shearing of the photospheric magnetic field, which fed the energy into the filament, was rapid. It is proposed that fast-moving Hα features must have initiated the observed coronal transients. From Hα, type II and coronal-transient observations, we estimate a magnetic field of 2.8 G at 1.9R⊙ from the disc centre, which agrees well with the earlier results.  相似文献   

18.
The time variation and latitude dependence of the solar rotation are found using observational data on Hα filaments and compact magnetic features with different polarities during solar activity cycles 20 and 21 (1966–1985). Statistical analysis of the observational data shows that there is a north–south asymmetry in the rotation, both for the Hα filaments and for compact magnetic features (structures) with negative and positive polarities. The N-S asymmetry in the differential rotation of the Hα filaments and the compact magnetic features with both polarities shows up quite distinctly in solar activity cycles 20 and 21, but the asymmetry for the compact magnetic features with positive polarity is comparatively lower in cycle 21. The confidence level is lower the compact magnetic features with positive polarity than for the compact magnetic features with negative polarity.  相似文献   

19.
Yu Liu 《Solar physics》2008,249(1):75-84
Liu et al. (Astrophys. J. 628, 1056, 2005a) described one surge – coronal mass ejection (CME) event showing a close relationship between solar chromospheric surge ejection and CME that had not been noted before. In this work, large Hα surges (>72 Mm, or 100 arcsec) are studied. Eight of these were associated with CMEs. According to their distinct morphological features, Hα surges can be classified into three types: jetlike, diffuse, and closed loop. It was found that all of the jetlike surges were associated with jetlike CMEs (with angular widths ≤30 degrees); the diffuse surges were all associated with wide-angle CMEs (e.g., halo); the closed-loop surges were not associated with CMEs. The exclusive relation between Hα surges and CMEs indicates difference in magnetic field configurations. The jetlike surges and related narrow CMEs propagate along coronal fields that are originally open. The unusual transverse mass motions in the diffuse surges are suggested to be due to magnetic reconnections in the corona that produce wide-angle CMEs. For the closed-loop surges, their paths are just outlining stable closed loops close to the solar surface. Thus no CMEs are associated with them.  相似文献   

20.
The behavior of oscillations in the quite solar chromosphere under a coronal hole at several heights has been investigated. The properties of oscillations in cell, network, and weak-floccule areas have been analyzed. A time series of spectrograms in three ionized calcium lines, the Ca II K and H resonance doublet lines and the infrared Ca II 849.8-nm triplet line, was used. The observations were carried out at the horizontal solar telescope of the Sayan Observatory. The goal of this study was to compare the distributions of spectral power in various frequency ranges and their variations for selected spatial areas at different heights of the chromosphere. Particular attention was paid to the weak floccule due to a noticeable difference in the central intensity distribution between the K and H lines and the 849.8-nm line. A spectral Fourier analysis was used. The central intensities of the observed spectral lines, the K-index, and the equivalent width (the latter for the 849.8-nm line) were chosen as oscillation parameters. The studies have shown that the main intensity oscillation power at both atmospheric levels is concentrated at frequencies below 9 mHz. In the distribution of intensity oscillation power at different chromospheric levels, there are differences clearly distinguishable in the floccule. Powerful five-minute oscillations whose main peak frequency decreases with height, while the amplitude increases have been detected in the central part of the floccule. This result confirms the assumptions recently pointed out in the literature that vertical magnetic field concentrations can serve as a channel for the passage of low-frequency oscillations from the photosphere to the chromosphere in faculae. The intensity oscillation power in the frequency ranges under consideration has turned out to decrease with height, on average, for the entire observed spatial area. This may be related to the loss of part of the wave energy through the reflection, dissipation, and transformation of wave modes in the magnetic canopy layer. An area with a low brightness but powerful oscillations at about 3.3 mHz covering a considerable range of heights probably pertaining to “magnetic flashers” has been isolated in the telescope’s field of view.  相似文献   

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