共查询到20条相似文献，搜索用时 78 毫秒
1.
On 5 April 2008, a filament at the periphery of an active region was observed by the Extreme Ultraviolet Imager telescope aboard the STEREO-A spacecraft, which showed up as a prominence eruption in the field-of-view from STEREO-B. The filament at STEREO-A 304 Å was first lengthened toward a region with weak overlying magnetic field so evolved as a large-scale one consisting of bright and dark threads twisting with each other, and then the portion below the weak field underwent an eruption. Meanwhile, the corresponding STEREO-B 304 Å prominence threads exhibited a kinking structure and tilting motion, with its center deflecting from the radial direction. By using three-dimension (3D) reconstruction technology, we obtain the 3D topology for the kinked prominence when its apex arrived at 1.4 radii, from which a clockwise rotation of about 90° is found in the course of the eruption. By comparing the 3D structure with the magnetic-field configuration computed by using the Potential-Field Source-Surface (PFSS) model, it is suggested that the filament erupted against the rather weaker than stronger overlying magnetic field, which make it appear to tilt toward one side. 相似文献
2.
We study the periodicity of twisting motions in sunspot penumbral filaments, which were recently discovered from space (Hinode) and ground-based (SST) observations. A sunspot was well observed for 97 minutes by Hinode/SOT in the G-band (4305 Å) on 12 November 2006. By the use of the time?–?space gradient applied to intensity space?–?time plots, twisting structures can be identified in the penumbral filaments. Consistent with previous findings, we find that the twisting is oriented from the solar limb to disk center. Some of them show a periodicity. The typical period is about ≈?four minutes, and the twisting velocity is roughly 6 km s?1. However, the penumbral filaments do not always show periodic twisting motions during the time interval of the observations. Such behavior seems to start and stop randomly with various penumbral filaments displaying periodic twisting during different intervals. The maximum number of periodic twists is 20 in our observations. Studying this periodicity can help us to understand the physical nature of the twisting motions. The present results enable us to determine observational constraints on the twisting mechanism. 相似文献
3.
Vasso Agapitou John C. B. Papaloizou 《Monthly notices of the Royal Astronomical Society》2000,317(2):273-288
We calculate the structure of a force-free magnetosphere which is assumed to corotate with a central star and which interacts with an embedded differentially rotating accretion disc. The magnetic and rotation axes are aligned, and the stellar field is assumed to be a dipole. We concentrate on the case when the amount of field line twisting through the disc–magnetosphere interaction is large , and consider different outer boundary conditions. In general the field line twisting produces field line inflation (e.g. Bardou & Heyvaerts), and in some cases with large twisting many field lines can become open. We calculate the spin-down torque acting between the star and the disc, and we find that it decreases significantly for cases with large field line twisting. This suggests that the oscillating torques observed for some accreting neutron stars could be caused by the magnetosphere varying between states with low and high field line inflation. Calculations of the spin evolution of T Tauri stars may also have to be revised in the light of the significant effect that field line twisting has on the magnetic torque resulting from star–disc interactions. 相似文献
4.
《天文和天体物理学研究(英文版)》2015,(10)
Study of the small-scale structures and material flows associated with solar quiescent filaments is very important for understanding the formation and equilibrium of solar filaments.Using high resolution Ha data observed by the New Vacuum Solar Telescope,we present the structures of barbs and material flows along the threads across the spine in two quiescent filaments on 2013 September 29 and on 2012 November 2,respectively.During the evolution of the filament barb,several parallel tube-shaped structures formed and the width of the structures ranged from about2.3 Mm to 3.3 Mm.The parallel tube-shaped structures merged together accompanied by material flows from the spine to the barb.Moreover,the boundary between the barb and surrounding atmosphere was very neat.The counter-streaming flows were not found to appear alternately in the adjacent threads of the filament.However,the large-scale patchy counter-streaming flows were detected in the filament.The flows in one patch of the filament have the same direction but flows in the adjacent patch have opposite direction.The patches of two opposite flows with a size of about 10" were alternately exhibited along the spine of the filament.The velocity of these material flows ranged from 5.6 km s~(-1) to 15.0 km s~(-1).The material flows along the threads of the filament did not change their direction for about two hours and fourteen minutes during the evolution of the filament.Our results confirm that the large-scale counterstreaming flows with a certain width along the threads of solar filaments exist and are coaligned well with the threads. 相似文献
5.
The vertical fine structure in a quiescent prominence was modelled as an assembly of very narrow, optically thin threads. Random clusterings of the threads can account for the observed contrast and H line profiles of the fine structures. In this picture, each structure consists of a cluster of 7–20 elementary threads.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.NAS/NRC Research Associate, on leave from Institut d'Astrophysique, CNRS, Paris, France. 相似文献
6.
J. McKim Malville 《Solar physics》1976,50(1):79-83
Ions falling in vertically aligned magnetic structures of quiescent prominences may experience a vertical Lorentz force as flux ropes are distorted from the force-free condition. The terminal velocity of such ions may be sub-Alfvénic and may correspond to the 5–15 km s–1 velocity of down falling material observed in many quiescent prominences. The higher velocities of down falling material found in active prominences and coronal rain may occur because of higher terminal velocities occurring in stronger magnetic fields.Visiting Astronomer, on leave from the Department of Astro-Geophysics, University of Colorado, Boulder, Colorado 80309. 相似文献
7.
Kunitomo Sakurai 《Solar physics》1976,47(1):261-266
The magnetic polarity distributions in sunspot groups which produced solar proton flares have been analyzed. It is shown that the fluid motion in sunspot groups and below may be responsible for the origin of inverted or unusual polarity distributions, since rotating motion in these spot groups is often observed. Since such motion seems to produce twisting of magnetic field lines above sunspot groups, the origin of solar flares seems to be closely dependent on instability associated with this twisting of sunspot field lines in the chromosphere and the lower corona. 相似文献
8.
In a previous paper, we suggested that the twisting of coronal magnetic fiels by photospheric motions produces the steady heating of an active region, while braiding of these fields stores energy which is eventually released in an avalanche process, as sporadic large flares. We explore these ideas with numerical simulations. Our results indicate that the combined effect of twisting and braiding can account for the observed power input and the flare frequency spectrum of typical active regions.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under coooperative agreement with the National Science Foundation. 相似文献
9.
In this paper we will show that the twisting mechanism of Sturrock and Uchida is as viable a heating source for the active corona as Parker's braiding. This conclusion contradicts that of Berger (1990). Moreover, we shall show that if we adopt Berger's criterion for reconnection, braiding produces far more flare energy than is observed. A modified criterion, consistent with twisting, produces insufficient heating but, coupled to an avalanche process, could account for active region flares.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. 相似文献
10.
Thin Threads of Solar Filaments 总被引：1，自引：0，他引：1
High-resolution images obtained in H with the new Swedish Solar Telescope at La Palma, Spain, have been used for studies of fine-scale threads in solar filaments. The widths of the thin threads are 0.3 arcsec. The fact that the width of the thinnest threads is comparable to the diffraction limit of the telescope of about 0.14 arcsec, at the wavelength of H, suggests that even thinner threads may exist. Assuming that the threads represent thin magnetic strings, we conclude that only a small fraction of these are filled with observable absorbing plasma, at a given time. The absorbing plasma is continuously flowing along the thread structures at velocities 15± 10 kms–1, which suggests that the flows must be field-aligned. In one case where a bundle of thin threads appears to be rooted in the nearby photosphere, we find that the individual threads connects with intergranular, dark lanes in the photosphere. We do not find signs of typical network fields at the roots of the fine threads, as normally evidenced by bright points in associated G-band images. It is suggested that filament threads are rooted in relatively weak magnetic fields. 相似文献
11.
High-resolution Hα filtergrams (0.2″) obtained with the Swedish 1-m Solar Telescope resolve numerous very thin, thread-like
structures in solar filaments. The threads are believed to represent thin magnetic flux tubes that must be longer than the
observable threads. We report on evidence for small-amplitude (1 – 2 km s−1) waves propagating along a number of threads with an average phase velocity of 12 km s−1 and a wavelength of 4″. The oscillatory period of individual threads vary from 3 to 9 minutes. Temporal variation of the
Doppler velocities averaged over a small area containing a number of individual threads shows a short-period (3.6 minutes)
wave pattern. These short-period oscillations could possibly represent fast modes in accordance with numerical fibril models
proposed by Díaz et al. (Astron. Astrophys.
379, 1083, 2001). In some cases, it is clear that the propagating waves are moving in the same direction as the mass flows. 相似文献
12.
Chiuderi Drago F. Alissandrakis C.E. Bastian T. Bocchialini K. Harrison R.A. 《Solar physics》2001,199(1):115-132
In this paper we compare simultaneous extreme ultraviolet (EUV) line intensity and microwave observations of a filament on the disk. The EUV line intensities were observed by the CDS and SUMER instruments on board SOHO and the radio data by the Very Large Array and the Nobeyama radioheliograph. The main results of this study are the following: (1) The Lyman continuum absorption is responsible for the lower intensity observed above the filament in the EUV lines formed in the transition region (TR) at short wavelengths. In the TR lines at long wavelengths the filament is not visible. This indicates that the proper emission of the TR at the filament top is negligible. (2) The lower intensity of coronal lines and at radio wave lengths is due to the lack of coronal emission: the radio data supply the height of the prominence, while EUV coronal lines supply the missing hot matter emission measure (EM). (3) Our observations support a prominence model of cool threads embedded in the hot coronal plasma, with a sheath-like TR around them. From the missing EM we deduce the TR thickness and from the neutral hydrogen column density, derived from the Lyman continuum and Hei absorption, we estimate the hydrogen density in the cool threads. 相似文献
13.
A new method for the calculation of coronal magnetic field is proposed and it is shown to reproduce the EUV features in the corona as observed by Skylab experiments satisfactorily well. One of the remarkable points is that it reproduces the loopy threads in the active region corona and also the large scale field lines connecting active regions. The existence of coronal current is expected wherever the present coronal-current-free model fails to represent the feature. A method of calculating the coronal sheet-current is also developed with the purpose of knowing the shape of the current sheet and the amount of magnetic stress energy stored due the the presence of it by comparing the calculated field configuration with the observed local distortion of the EUV threads. This may be used in pinning down the possible site of the flare and in discussing the flare occurrence in terms of the energy stored there.During the preparation of this work, Poletto et al. (1975) calculated the magnetic field shape in Schmidt's method to compare with the soft X-ray feature obtained by Skylab. 相似文献
14.
Peter Foukal 《Solar physics》1971,20(2):298-309
The physical characteristics of the H structures previously defined as fibrils and threads are studied. The interpretation of the fibrils as ends of flux tubes is useful in tracing the behavior of the transverse field component over the solar surface.The observed properties of fibrils and threads are consistent with the hypothesis that they are produced by a shock wave mechanism similar to that advanced by Parker to explain spicules. It is suggested that the undisturbed magnetic field in the chromosphere of an active region is confined to a thin sheath, while the field of the quiet regions extends into the corona. 相似文献
15.
Observations of reversed-polarity features in the chromosphere as well as in the photosphere in the form of magnetic gulfs or islands of opposite polarity have been reported recently. In this paper, we present a possible explanation for the appearance of reversed-polarity features observed in the chromospheric magnetograms of the NOAA AR 7321 observed during October 25–27, 1992. It is suggested that the large-scale reversed-polarity features may occur due to the twisting of the smaller-scale magnetic flux tubes in the layer between the photosphere and the chromosphere. 相似文献
16.
Filtergrams spanning Hα ± 4.1 Å, supplemented with observations at 2.8 and 3 GHz, are used variously to describe the onset, dormancy, and flash phase of this 2b flare. Among the phenomena observed are 17- and 23-sec periodic pulsations in the microwave data early in the flare and formation of perpendicular, overlapping threads of red-shifted and blue-shifted material late in the flare. 相似文献
17.
Peter Foukal 《Solar physics》1971,19(1):59-71
A continuous relationship is proposed between the basic elements of the dark fine structure of the quiet and active chromosphere. A progression from chromospheric bushes to fibrils, then to chromospheric threads and active region filaments, and finally to diffuse quiescent filaments, is described. It is shown that the horizontal component of the field on opposite sides of an active region quiescent filament can be in the same direction and closely parallel to the filament axis. Consequently, it is unnecessary to postulate twisted or otherwise complex field configurations to reconcile the support mechanism of filaments with the observed motion along their axis. 相似文献
18.
E. N. Parker 《Astrophysics and Space Science》1976,44(1):107-117
It is shown that the mean longitudinal field in a magnetic flux tube is reduced, rather than enhanced, by twisting the tube to form a rope. It is shown that there is no magnetohydrostatic equilibrium when one twisted rope is wound around another. Instead there is rapid line cutting (neutral point annihilation). It is shown that the twisting increases, and the field strength decreases, along a flux tube extending upward through a stratified atmosphere.These facts are at variance with Piddington's recent suggestion that solar activity is to be understood as the result of flux tubes which are enormously concentrated by twisting, which consist of several twisted ropes wound around each other, and which came untwisted where they emerge through the photosphere.This work was supported in part by the National Aeronautics and Space Administration under Grant NGL 14-001-001. 相似文献
19.
We present observations of the formation process of a small-scale filament on the quiet Sun during 5?–?6 February 2016 and investigate its formation cause. Initially, a small dipole emerged, and its associated arch filament system was found to reconnect with overlying coronal fields accompanied by numerous extreme ultraviolet bright points. When the bright points faded, many elongated dark threads formed and bridged the positive magnetic element of the dipole and the external negative network fields. Interestingly, an anticlockwise photospheric rotational motion (PRM) set in within the positive endpoint region of the newborn dark threads following the flux emergence and lasted for more than 10 hours. Under the drive of the PRM, these dispersive dark threads gradually aligned along the north-south direction and finally coalesced into an inverse S-shaped filament. Consistent with the dextral chirality of the filament, magnetic helicity calculations show that an amount of negative helicity was persistently injected from the rotational positive magnetic element and accumulated during the formation of the filament. These observations suggest that twisted emerging fields may lead to the formation of the filament via reconnection with pre-existing fields and release of its inner magnetic twist. The persistent PRM might trace a covert twist relaxation from below the photosphere to the low corona. 相似文献
20.
The jets observed to emanate from many compact accreting objects may arise from the twisting of a magnetic field threading
a differentially rotating accretion disk which acts to magnetically extract angular momentum and energy from the disk. Two
main regimes have been discussed, hydromagnetic jets, which have a significant mass flux and have energy and angular momentum
carried by both matter and electromagnetic field and, Poynting jets, where the mass flux is small and energy and angular momentum
are carried predominantly by the electromagnetic field. Here, we describe recent theoretical work on the formation of relativistic
Poynting jets from magnetized accretion disks. Further, we describe new relativistic, fully electromagnetic, particle-in-cell
(PIC) simulations of the formation of jets from accretion disks. Analog Z-pinch experiments may help to understand the origin
of astrophysical jets. 相似文献