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1.
Solar observations show that magnetic reconnection can occur in the Sun's weakly ionized lower atmosphere (magnetic cancellation, Ellerman bombs and type II white-light flares). Unlike what the usual reconnection models have predicted, such a reconnection is accompanied by temperature enhancements which are less than 10%. To overcome this difficulty, we have reexamined the reconnection in a two-fluid model using a 2D numerical simulation. The numerical solutions demonstrate the following results: (1) Under the influence of Lorentz force, ionized gas carries the magnetic field into a diffusion region where part of the field is annihilated, and the current-sheet scaling laws for the weakly ionized plasma are basically the same as in the fully ionized case. (2) Though the neutral gas is not directly affected by the magnetic field due to frictional forces, its motion is almost the same as the ionized gas except in the region near stagnation point where the streamlines of both species differ appreciably. (3) The pressure of neutrals which governs the distribution of total pressure and temperature varies slightly. So the temperature of the whole domain is nearly uniform in space and constant in time. These results support the idea that magnetic cancellation, Ellerman bombs, and type II white-light flares are due to magnetic reconnection in the Sun's lower atmosphere. 相似文献
2.
王水 《紫金山天文台台刊》1994,13(3):181-188
Basic processes of magnetic reconnection and observations of coronal mass ejection are introduced. A possible mechanism of CME caused by magnetic rcconnection in the current sheet of solar corona is suggested. 相似文献
3.
A model of forced magnetic reconnection in a force-free magnetic field is considered, which allows calculation of the magnetic
energy release during the current sheet reconnection. The dependence of this energy on characteristics of the magnetic configuration
has been studied, and it was found that the released energy becomes very large when the field is near the marginal tearing
stability. A persistent plasma heating provided by ongoing external driving and internal reconnection is also derived. It
shows a typical relaxation-type dependence on the driving frequency, with dissipation becoming most efficient when the time-scales
of the driving and reconnection are comparable. Possible implications of the obtained results for the problem of solar coronal
heating are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
E.R. Priest 《Astrophysics and Space Science》1998,264(1-4):77-100
Here I review briefly the theory of magnetohydrodynamic reconnection and ask what observational evidence is there that it
is heating the corona. In particular, the new directions in which three-dimensional theory for reconnection is heading are
outlined. Part of the coronal heating problem has been solved with the identification of reconnection driven by converging
flux motions as the key for x-ray bright points. Furthermore, it has been shown that the large-scale diffuse corona is heated
rather uniformly, so that turbulent reconnection by braiding or ion-cyclotron waves driven by network micro-flares are prime
candidates. Finally, reconnection is the natural explanation for a wide variety of phenomena discovered by SOHO including
explosive events, blinkers, the magnetic carpet and even possibly tornadoes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
总结了近期用射电频谱仪(高时间和高频谱分辨)和野边山射电日像仪(高空间分辨)以及国内外其它空间和地面设备分析日冕磁场和重联的系列工作。主要结论可归纳为:1)在Dulk等人(1982)的近似下自恰计算射电爆发源区磁场的平行和垂直分量,并首次得到该磁场在日面的两雏分布。2)为了考虑非热电子低能截止的影响,必须采用更严格的回旋同步辐射理论来计算。结果表明:低能截止和日冕磁场对计算有明显的影响,而其它参数(包括背景温度、密度、高能截止和辐射方向)的影响均可忽略。因此,对低能截止和日冕磁场必须联立求解。3)射电爆发中的精细结构可能反映了射电爆发源比较靠近粒子加速(磁场重联)的区域,利用高时间和高频率分辨的频谱仪和高空间分辨的日像仪联合分析,可以确定精细结构的源区位置,从而确定粒子加速(磁场重联)的准确时间和地点。 相似文献
6.
A short summary of recent progress in measuring and understanding turbulence during magnetic reconnection in laboratory plasmas
is given. Magnetic reconnection is considered as a primary process to dissipate magnetic energy in laboratory and astrophysical
plasmas. A central question concerns why the observed reconnection rates are much faster than predictions made by classical
theories, such as the Sweet–Parker model based on MHD with classical Spitzer resistivity. Often, the local resistivity is
conjectured to be enhanced by turbulence to accelerate reconnection rates either in the context of the Sweet–Parker model
or by facilitating setup of the Pestchek model. Measurements at a dedicated laboratory experiment, called MRX or Magnetic
Reconnection Experiment, have indicated existence of strong electromagnetic turbulence in current sheets undergoing fast reconnection.
The origin of the turbulence has been identified as right-hand polarized whistler waves, propagating obliquely to the reconnecting
field, with a phase velocity comparable to the relative drift velocity. These waves are consistent with an obliquely propagating
electromagnetic lower-hybrid drift instability driven by drift speeds large compared to the Alfven speed in high-beta plasmas.
Interestingly, this instability may explain electromagnetic turbulence also observed in collisionless shocks, which are common
in energetic astrophysical phenomena. 相似文献
7.
This paper is devoted to the numerical approximation of the discontinuous solutions of the Euler equations for weakly ionized mixtures of reacting gases. The main difficulty stems from the non conservative formulation of these equations due to a widely used physical assumption. We show how to derive a well-posed conservative reformulation of the equations from the analysis of the associated full convective-diffusive system. We then propose an exact Roe-type linearization for the equivalent system of conservation laws on the basis of an original Lemma for averagings. Our results can be seen as an extension of the classical Roe average, for nonlinearities that cannot be recast under quadratic form. This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
In this paper we present a new class of exact reconnection solutions in cylindrical geometry. We point out that in the case of planar reconnection there is a natural cylindrical analog to the Cartesian Dawson function model for the magnetic field. Although the resistive energy release scalings of these solutions mimic the Cartesian models an important new feature is the presence of curvature in the current sheet. We go on to show that these solutions can be generalized to three dimensions. 相似文献
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11.
Shou-Biao Zhang Jin-Lin Xie Guang-Hai Hu Hong Li Guang-Li Huang Wan-Dong Liu 《Chinese Astronomy and Astrophysics》2011,35(4):339-348
In the Linear Magnetized Plasma (LMP) device of University of Science and Technology of China and by exerting parallel currents on two parallel copper plates, we have realized the magnetic reconnection in laboratory plasma. With the emissive probes, we have measured the parallel (along the axial direction) electric field in the process of reconnection, and verified the dependence of reconnection current on passing particles. Using the magnetic probe, we have measured the time evolution of magnetic flux, and the measured result shows no pileup of magnetic flux, in consistence with the result of numerical simulation. 相似文献
12.
Various topological features, for example magnetic null points and separators, have been inferred as likely sites of magnetic reconnection and particle acceleration in the solar atmosphere. In fact, magnetic reconnection is not constrained to solely take place at or near such topological features and may also take place in the absence of such features. Studies of particle acceleration using non-topological reconnection experiments embedded in the solar atmosphere are uncommon. We aim to investigate and characterise particle behaviour in a model of magnetic reconnection which causes an arcade of solar coronal magnetic field to twist and form an erupting flux rope, crucially in the absence of any common topological features where reconnection is often thought to occur. We use a numerical scheme that evolves the gyro-averaged orbit equations of single electrons and protons in time and space, and simulate the gyromotion of particles in a fully analytical global field model. We observe and discuss how the magnetic and electric fields of the model and the initial conditions of each orbit may lead to acceleration of protons and electrons up to 2 MeV in energy (depending on model parameters). We describe the morphology of time-dependent acceleration and impact sites for each particle species and compare our findings to those recovered by topologically based studies of three-dimensional (3D) reconnection and particle acceleration. We also broadly compare aspects of our findings to general observational features typically seen during two-ribbon flare events. 相似文献
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14.
J. Büchner 《Astrophysics and Space Science》1998,264(1-4):25-42
Reconnection is the most efficient way to release the energy accumulated in the tense astrophysical magnetoplasmas. As such
it is a basic paradigm of energy conversion in the universe. Astrophysical reconnection is supposed to heat plasmas to high
temperatures, it drives fast flows, winds and jets, it accelerates particles and leads to structure formation. Reconnection
can take place only after a local breakdown of the plasma ideality, enabling a change of the magnetic connection between plasma
elements. After Giovanelli first suggested magnetoplasma discharges in 1946, reconnection has usually been identified with
vanishing magnetic field regions. However, for the last ten years a discussion has been going on about the structure of 3
D reconnection, e.g., whether in 3 D it is possible also without magnetic nulls or not. We first shortly review the relevant
magnetostatic and kinematic fluid theory results to argue than that a kinetic approach is necessary to reveal the generic
three-dimensional structure and dynamics of reconnection in collisionless astrophysical plasmas. We present results about
the 3 D structure of kinetic reconnection in initially antiparallel magnetic fields. They were obtained by selfconsistently
considering ion and electron inertia as well as dissipative wave-particle resonances. In this approach reconnection is a natural
consequence of the instability of thin current sheets. We present the results of a nonlocal linear dispersion theory and describe
the nonlinear evolution of the instability using numerical particle code simulations. The decay of thin current sheets directly
leads to a configurational instability and three-dimensional dynamic reconnection. We report the resulting generic magnetic
field structure. It contains pairs of magnetic nulls, connected by separating magnetic flux surfaces through which the plasma
flows and along which reconnection induces large parallel electric fields. Our results are illustrated by virtual reality
views and movies, both stored on the attached CD-ROM and also being available from the Internet.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
The ability of magnetic reconnection solutions to explain statistical flare data is discussed. It is assumed that flares occur at well-defined, isolated sites within an active region, determined by the null points and separators of the coronal magnetic field (Craig, 2001). Statistical flare observations then derive from a multiplicity of independent sites, flaring in parallel, that produce events of widely varying output (Wheatland, 2002). Given that the `separator length' at an individual site controls the event frequency and the mean energy release, it is shown that the observed frequency-energy spectrum N(E)can be inverted to yield a source function that relates directly to the distribution of separator lengths. It is also pointed out that, under the parallel flaring model, inferred waiting-time distributions are naturally interpreted as a superposition of individual point processes. Only a modest number of flaring separators is required to mimic a Poisson process. 相似文献
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太阳大气中磁重联的MHD数值模拟 总被引:1,自引:0,他引:1
回顾了近30年太阳大气中磁重联过程的MHD数值模拟工作取得的进展。着重描述了在验证理论模型,解释观测现象,以及研究各种因素对重联的影响三个方面的成果,如快速磁重联,太阳耀斑机制及色球,日冕中的各种爆发现象等。指出了在数值模拟中应注意的几个问题,并对该领域今后的发展作了简要的展望。 相似文献
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In weakly ionized astrophysical plasmas, shear flow induced plasma - neutral gas friction yields self-generated magnetic fields
of seed-field order. This process is of cosmological importance and relevant for protogalactic systems like Lyα-clouds. In
our contribution we illustrate this mechanism by the help of 3-dimensional 2-fluid simulations of primordial rotating gas
clumps in Lyα-clouds showing that plasma - neutral gas interactions cause large scale magnetic fields of the order of 10−15G on time scales of the order of 106yrs.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献