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1.
Vector magnetogram and dopplergram observation of magnetic flux emergence and its explanation 总被引：1，自引：0，他引：1
During 23–28 August 1988, at the Huairou Solar Observation Station of Beijing Observatory, the full development process of the region HR 88059 was observed. It emerged near the center of the solar disk and formed a medium active region. A complete series of vector magnetograms and photospheric and chromospheric Dopplergrams was obtained. From an analysis of these data, combined with some numerical simulations, the following conclusions can be drawn. (1) The emergence of new magnetic flux from enhanced networks followed by sunspot formation is an interesting physical process which can be simply described by MHD numerical simulation. The phenomena accompanying it occur according to a definite law summarized by Zwaan (1985). The condition for gas cooling and sunspot formation seems to be transverse field strength > 50 G together with longitudinal field strength > 700 G. For a period of 4 to 5 hours, the orientation of the transverse field shows little change. The configuration of field lines may be derived from vector magnetograms. The arch filament system can be recognized as an MHD shock. (2) New opposite bipolar features emerge within the former bipolar field with an identical strength which will develop a sunspot group complex. Also, arch filament systems appear there located in the position of flux emergence. The neutral line is often pushed aside and curved, leading to faculae heating and the formation of a current sheet. In spite of complicated Dopplergrams, the same phenomena occur at the site of flux emergence as usual: upward flow appears at the location of the emerging and rapidly varying flux near the magnetic neutral line, and downdraft occurs over large parts of the legs of the emerging flux tubes. The age of magnetic emerging flux (or a sunspot) can be estimated in terms of transverse field strengths: when 50 G < transverse field < 200 G, the longitudinal magnetogram and Dopplergram change rapidly, which indicates a rigourously emerging magnetic flux. When the transverse field is between 200 and 400 G, the area concerned is in middle age, and some of the new flux is still emerging there. When the transverse field > 400 G, the variation of the longitudinal magnetogram slows down and the emerging arch becomes relatively stable and a photospheric Evershed flow forms at the penumbra of the sunspot. 相似文献
2.
Haimin Wang 《Solar physics》1992,140(1):85-98
This paper studies the evolution of vector magnetic fields in the active region Boulder No. 6233 during an 11-hour observing period and its relationship to an X-3 flare on August 27, 1990.We observed the evolution of magnetic fields, which includes magnetic shear build-up, directly in high-resolution vector magnetograph movies. The magnetic shear is observed to be built up in two ways: (1) shear motion between two poles of opposite magnetic polarities and (2) direct collision of two poles of opposite polarities. When two magnetic elements of opposite polarities are canceling, the field lines are observed to turn from direct connection (potential) to a sheared configuration during the process.An X-3 flare occurred at 2100 UT. The vector magnetic structure showed an unexpected pattern of changes during and after the flare. The shear (defined as the angle between the measured transverse field and the calculated potential field) in the area covering two major footpoints increased rapidly coinciding with the burst of GOES X-ray flux. While the flare faded away in about one hour, the high shear status dropped slowly for the remainder of the observing period. Immediately after the flare, new flux emerged more rapidly and the flow speed of several magnetic elements increased near the flare footpoints.In this active region and a few other flare-productive regions we have studied recently, we always find rapid and complicated flow motions near the sites where flares occur. Photospheric flows appear to be another important factor for the production of flares. 相似文献
3.
Hong-Qi ZhangNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2004,4(6):563-577
We analyze the process of formation of delta configuration in some well-known super active regions based on photospheric vector magnetogram observations. It is found that the magnetic field in the initial developing stage of some delta active regions shows a potential-like configuration in the solar atmosphere, the magnetic shear develops mainly near the magnetic neutral line with magnetic islands of opposite polarities, and the large-scale photospheric twisted field forming gradually later. Some results are obtained: (1) The analysis of magnetic writhe of whole active regions cannot be limited in the strong field of sunspots, because the contribution of the fraction of decayed magnetic field is non-negligible. (2) The magnetic model of kink magnetic ropes, supposed to be generated in the subatmosphere, is not consistent with the evolution of large-scale twisted photospheric transverse magnetic field and not entirely consistent with the relationship with magnetic shear in some delta active regions. (3) T 相似文献
4.
Nabil T. Eldabe Mahmoud A. Mahmoud Gamal M. A. El Rahman 《Astrophysics and Space Science》1991,178(2):197-204
In this paper, the nonsteady flow of non-Newtonian power-law conducting fluid through a porous medium past an infinite porous plate is investigated. The system is stressed by a constant transverse magnetic field. The velocity outside the boundary layer depends exponentially on time. The rheological effects are shown and discussed on the shear stress in terms of rheological parameter of power-law fluid. The approximate solution in a closed form were obtained by using the Galerkin method. Also the effect of the magnetic field and permeability parameter are discussed. 相似文献
5.
H. Q. Zhang 《Astrophysics and Space Science》2006,305(3):211-224
We discuss the study of solar magnetic fields based on the photospheric vector magnetograms of solar active regions which were obtained at Huairou Solar Observing Station near Beijing in the period of 22nd and 23th solar cycles. The measurements of the chromospheric magnetic field and the spatial configuration of the field at the lower solar atmosphere inferred by the distribution of the solar photospheric and chromospheric magnetic field. After the analysis on the formation process of delta configuration in some super active regions based on the photospheric vector magnetogram observations, some results are obtained: (1) The analysis of magnetic writhe of whole active regions cannot be limited in the strong field of sunspots, because the contribution of the fraction of decayed magnetic field is non-negligible. (2) The magnetic model of kink magnetic ropes, proposed to be generated in the subatmosphere, is not consistent with the evolution of large-scale twisted photospheric transverse magnetic field and the relationship with magnetic shear in some delta active regions completely. (3) The proposition is that the large-scale delta active regions are formed from contribution by highly sheared non-potential magnetic flux bundles generated in the subatmosphere. We present some results of a study of the magnetic helicity. We also compare these results with other data sets obtained by magnetographs (or Stokes polarimeters) at different observatories, and analyze the basic chirality of the magnetic field in the solar atmosphere. 相似文献
6.
The present MSFC Vector Magnetograph has sufficient spatial resolution (2.7 arcsec pixels) and sensitivity to the transverse field (the noise level is about 100 gauss) to map the transverse field in active regions accurately enough to reveal key aspects of the sheared magnetic fields commonly found at flare sites. From the measured shear angle along the polarity inversion line in sites that flared and in other shear sites that didn't flare, we find evidence that a sufficient condition for a flare to occur in 1000 gauss fields in and near sunspots is that both (1) the maximum shear angle exceed 85 degrees and (2) the extent of strong shear (shear angle > 80 degrees) exceed 10,000 km. 相似文献
7.
Using a two-dimensional, dissipative magnetohydrodynamic model, this paper presents a numerical simulation of the magnetic energy buildup in a quadrupolar field by photospheric shear motion. When electric current density is larger than a certain critical value, an anomalous resistivity is introduced in order to account for the dissipation caused by instabilities in high current regions. It is shown that like a bipolar field, a quadrupolar field can efficiently store magnetic free energy through photospheric shear motion. Electric current formed by shear concentrates on the separatrix and magnetic loops rooted in areas where the shear velocity gradient is large. The atmosphere is heated by anomalous resistive dissipation during the shear. Both magnetic and thermal energy increases nonlinearly with shearing displacement. When the anomalous resistivity increases or the critical current density decreases, the growth rate reduces for magnetic energy but goes up for thermal energy. 相似文献
8.
Based on photospheric vector magnetograms obtained at Huairou Solar Observing Station (HSOS), non-potential characteristics of the magnetic field beneath the filament in active region NOAA 9077 are investigated. We focus on the structure and evolution of the magnetic field from 00:08 UT to 10:25 UT of 14 July before the Bastille event. Particular attention is paid to transverse field strength, shear degree and horizontal gradient of the line-of-sight magnetic field around the filament and filament channel. The following characteristics are found. (1) The magnetic non-potentiality has an obviously non-uniform distribution. The shear degree of the transverse field (Hagyard et al., 1984) is very large, up to 75° in some sites beneath the filament, such as the initial brightening site in TRACE 1600 Å images and the breaking site of the filament. The transverse field and the horizontal gradient of the line-of-sight field are very large in some parts corresponding to the hottest and continuously brightening portions. (2) The mean strength and mean shear angle of the transverse field and mean horizontal gradient of the line-of-sight field have obviously dropped in most parts beneath the filament for two hours before the filament eruption and onset of the X5.7/3B flare. After comparing simultaneous UV and EUV images, H filtergrams and Dopplergrams at solar atmosphere, we suggest that magnetic cancellation is likely to quickly transport the magnetic energy and complexity into the higher atmosphere in these two hours. This leads to magnetic instability in the filament and eventually causes the eruption of filament and onset of the flare. 相似文献
9.
宋慕陶 《中国天文和天体物理学报》1989,(1)
日珥的观测显示存在着强的磁场剪切分量,本文研究了剪切在日珥形成中的积极作用。首先计算一个二维偶极势场当脚根受对称剪切后产生怎样的物理现象。作了三种情形的数值模拟。计算表明产生蘑菇状流动是个普遍规律,在某些条件下将形成弧顶凹陷。为了说明蘑菇流的物理起因,我们探讨了演化初期的线性渐近解。保留一阶量下导出了剪切速度W_z和磁场剪切分量B_x的解析解,对二维流动V_x,V_y求出了近似解:流的振幅随时间指数增长。对于弧顶凹陷,给于了定性的说明:磁浮力-(1/c)J_xB_x和形变阻尼力(1/c)J_zB_x之间的相互作用导致弧预变平凹陷,并把剪切区磁力线打开成为开场。弧顶凹陷是形成日珥的重要条件。冕弧加热量的略微减小,产生初始的热不稳定性,在凹陷处物质凝聚温度降低,弧脚根处因色球受蒸发而流入的物质沿管上升进入弧顶陷阱,加剧了热不稳定性,物质进一步变密,温度再降,最终形成了日珥。 相似文献
10.
V. Urpin 《Monthly notices of the Royal Astronomical Society》1999,308(3):741-744
We consider the mean electromotive force and a dynamo-generated magnetic field, taking into account the stretching of turbulent magnetic field lines by a shear flow. Calculations are performed by making use of the second-order correlation approximation. In the presence of shear, the mirror symmetry of turbulence can be broken; thus turbulent motions become suitable for the generation of a large-scale magnetic field. Regardless of the shear law, turbulence can lead to a rapid amplification of the mean magnetic field. The growth rate of the mean magnetic field depends on the length-scale: it is faster for the fields with smaller length-scale. The mechanism considered is qualitatively different from the alpha dynamo, and can generate only a magnetic field that is inhomogeneous in the direction of flow. In contrast to the alpha dynamo, this mechanism also allows the generation of two-dimensional fields. The suggested mechanism may play an important role in the generation of magnetic fields in accretion discs, galaxies and jets. 相似文献
11.
The propagation of axisymmetric magnetohydrodynamic waves near the equatorial plane of the crust of a neutron star that is in a transverse magnetic field is considered. These waves are excited by a spatially limited excitation in the form of a transverse magnetic field applied to the inner boundary of the neutron star's crust. The magnetic fields and electric currents excited at the stellar surface by this wave beam are determined. 相似文献
12.
The effect of a transverse magnetic field and of the viscosity diffusion on the free-convection flow of an electrically-conducting incompressible fluid past a uniformally accelerated vertical plate is discussed. A finite difference method has been used to obtain a numerical solution. The influence of the various parameters on the flow field is discussed. 相似文献
13.
Richard L. Harkness Jr. 《Solar physics》1969,10(1):154-167
A linearized magnetohydrodynamic formalism is used to examine the propagation in two dimensions of transverse waves in a plasma in which is embedded a curl-free magnetic field. Only waves of frequency less than the ion cyclotron frequency are considered. The behavior of a wave packet near the magnetic neutral point is deduced from the general solution to the problem, which is found in terms of Bessel functions whose order is frequency dependent. It is shown that a disturbance propagates through the medium with a group velocity that decreases from the speed of light at large distances from the neutral point to zero at the neutral point, and that the amplitudes of the velocities associated with the disturbance diverge there. It is suggested that the stagnation of waves near the origin and the deformation of the magnetic field resulting from the large plasma-flow velocities may provide a clue to the formation of the magnetic neutral sheet required by several flare theories and a theory of the acceleration of cosmic rays. 相似文献
14.
15.
Fausto Cattaneo Nicholas H. Brummell Kelly S. Cline † 《Monthly notices of the Royal Astronomical Society》2006,365(3):727-734
We study the topology of field lines threading buoyant magnetic flux structures. The magnetic structures, visually resembling idealized magnetic flux tubes, are generated self-consistently by numerical simulation of the interaction of magnetic buoyancy and a localized velocity shear in a stably stratified atmosphere. Depending on the parameters, the system exhibits varying degrees of symmetry. By integrating along magnetic field lines and constructing return maps, we show that, depending on the type of underlying behaviour, the stages of the evolution, and therefore the degree of symmetry, the resulting magnetic structures can have field lines with one of three distinct topologies. When the x -translational and y -reflectional symmetries remain intact, magnetic field lines lie on surfaces but individual lines do not cover the surface. When the y symmetry is broken, magnetic field lines lie on surfaces and individual lines do cover the surface. When both x and y symmetries are broken, magnetic field lines wander chaotically over a large volume of the magnetically active region. We discuss how these results impact our simple ideas of a magnetic flux tube as an object with an inside and an outside, and introduce the concept of 'leaky' tubes. 相似文献
16.
Tuan-Hui Zhou Hai-Sheng Ji 《中国天文和天体物理学报》2009,9(3)
We give an extensive multi-wavelength analysis of an eruptive M1.0/1N class solar flare, which occurred in the active region NOAA 10044 on 2002 July 26. Our empha-sis is on the relationship between magnetic shear and flare shear. Flare shear is defined as the angle formed between the line connecting the centroids of the two ribbons of the flare and the line perpendicular to the magnetic neutral line. The magnetic shear is computed from vector magnetograms observed at Big Bear Solar Observatory (BBSO), while the flare shear is computed from Transition Region and Coronal Explorer (TRACE) 1700A images. By a detailed comparison, we find that: 1) The magnetic shear and the flare shear of this event are basically consistent, as judged from the directions of the transverse mag-netic field and the line connecting the two ribbons' centroids. 2) During the period of the enhancement of magnetic shear, flare shear had a fast increase followed by a fluctuated decrease. 3) When the magnetic shear stopped its enhancement, the fluctuated decreasing behavior of the flare shear became very smooth. 4) Hard X-ray (HXR) spikes are well correlated with the unshearing peaks on the time profile of the rate of change of the flare shear. We give a discussion of the above phenomena. 相似文献
17.
S. M. Rucinski 《Astrophysics and Space Science》1983,94(2):395-400
The effect of a uniform transverse magnetic field on the free-convection flow of an electrically conducting fluid past a uniformly accelerated infinite vertical porous plate is discussed. Finite-difference method has been used to obtain the solution of the governing equations when the Prandtl number is not equal to unity. The velocity profiles have been shown graphically for both cases, cooling and heating of the porous plate. The numerical values of the skin-friction are entered in table and the effects of the various parameter are discussed on the flow field. 相似文献
18.
汪景琇 《中国天文和天体物理学报》1986,(3)
本文对充满垂直均匀磁场的等温大气内的磁声重力波做了严格的解析分析,并将其通解表述成广义超几何函数的形式。该解可用于对磁大气内振荡现象的进一步数值模拟研究。对解的分析澄清了若干磁声重力波的传播性质。 相似文献
19.
The propagation of axisymmetric magnetohydrodynamic waves near the equatorial plane of the crust of a neutron star in a transverse magnetic field is considered. The magnetic field is perpendicular to the equatorial plane. The magnetic fields and electric currents excited by this wave beam at the stellar surface are determined. 相似文献
20.
The present model is proposed to study the effect of thickness of Harris sheet and strength of guide field on the evolution of magnetic islands and generation of turbulence in magnetic reconnection sites. The governing model equation has been derived using EMHD model in the presence of the equilibrium magnetic field, consisting of guide field and shear field in the Harris sheet. We have carried out a numerical simulation of the dynamical equation for magnetopause region parameters. Simulation results reveal that as the thickness of Harris sheet increases, the intensity of evolution of magnetic islands decreases, but with increasing strength of guide field, intensity gradually increases and at later times irregular structures are formed. These structures give the indication of turbulence in magnetic reconnection site. Further, we have calculated power spectrum, which follows power index \({\sim}\,{-}1.5\) in the inertial range. 相似文献