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arXiv 1205.0935astro-ph.SR
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太阳通量管中的表面阿尔芬波

Surface Alfven waves in solar flux tubes

M. Goossens, J. Andries, R. Soler, T. Van Doorsselaere, I. Arregui, J. Terradas

摘要:

磁流体动力学(MHD)波在太阳大气中普遍存在。阿尔芬波和磁声波是MHD波的特殊类型。这些波模是明显不同的,只有在无限范围的均匀等离子体中才具有纯粹的性质。由于等离子体的非均匀性,MHD波具有混合特性,不能被分类为纯阿尔文波或磁声波。然而,涡量是一个明确的阿尔芬波的压缩是磁声波。本文研究了一维非均匀直柱体在恒定磁场作用下的MHD波。对于一个分段恒定的密度分布,我们发现,基本径向模式的非轴对称波具有相同的属性作为表面阿尔芬波在一个真正的密度不连续。与无限大均匀等离子体中经典的阿尔芬波相反,涡量除圆柱边界外处处为零。如果用连续的密度变化来代替密度的不连续性,那么涡量就以不均匀的密度分布在整个区间上。与径向泛音不同,非轴对称波的基本径向模式不需要压缩就可以存在。在薄磁柱中,相速度介于内、外阿尔芬速度之间的非轴对称波的径向基模可视为表面阿尔芬波。相反,径向泛音可能与快类磁声模式有关。

英文摘要:

Magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. Alfven waves and magneto-sonic waves are particular classes of MHD waves. These wave modes are clearly different and have pure properties in uniform plasmas of infinite extent only. Due to plasma non-uniformity MHD waves have mixed properties and cannot be classified as pure Alfven or magneto-sonic waves. However, vorticity is a quantity unequivocally related to Alfven waves as compression is for magneto-sonic waves. Here, we investigate MHD waves superimposed on a one-dimensional non-uniform straight cylinder with constant magnetic field. For a piecewise constant density profile we find that the fundamental radial modes of the non-axisymmetric waves have the same properties as surface Alfven waves at a true discontinuity in density. Contrary to the classic Alfveen waves in a uniform plasma of infinite extent, vorticity is zero everywhere except at the cylinder boundary. If the discontinuity in density is replaced with a continuous variation of density, vorticity is spread out over the whole interval with non-uniform density. The fundamental radial modes of the non-axisymmetric waves do not need compression to exist unlike the radial overtones. In thin magnetic cylinders the fundamental radial modes of the non-axisymmetric waves with phase velocities between the internal and the external Alfven velocities can be considered as surface Alfven waves. On the contrary, the radial overtones can be related to fast-like magneto-sonic modes.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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