自相似演化磁云的动力学研究
Investigation of Dynamics of Self-Similarly Evolving Magnetic Clouds
摘要：
磁云是在太阳风中移动的“磁化等离子云”。MCs将磁通量和螺旋度从太阳转移出去。这些结构不是静止的，而是具有时间演化的特征。通常，考虑简化的MC模型。本研究的目的是调查更一般的，径向扩张的MC的动态。它们被认为是具有低等离子体β的柱对称磁结构。为了研究MC的演变自相似方法和数值方法。结果表明，在考虑自相似发展，圆柱对称磁结构的力量是平衡的。导出了微囊内磁场、等离子体速度、密度和压强的显式解析表达式。这些解的特征在于磁通量和螺旋度的守恒值。我们还研究了自相似演化的MC的动力学的数字代码“Graale”的装置。此外，还研究了它们在高密度、高等离子体β介质中的膨胀。结果表明，MC的物理参数保持其自相似的字符在其整个演化。结论.通过比较不同的自相似解和数值解，我们可以得出这样的结论：我们的自相似解可以很好地描述不断演化的MCs-它们在相当长的时间内以及在离太阳很远的地方都保持着自相似、相干的性质。
英文摘要：
Magnetic clouds (MCs) are "magnetized plasma clouds" moving in the solar wind. MCs transport magnetic flux and helicity away from the Sun. These structures are not stationary but feature temporal evolution. Commonly, simplified MC models are considered. The goal of the present study is to investigate the dynamics of more general, radially expanding MCs. They are considered as cylindrically symmetric magnetic structures with low plasma β. In order to study MC`evolution the self-similar approach method and a numerical approach are used. It is shown that the forces are balanced in the considered self-similarly evolving, cylindrically symmetric magnetic structures. Explicit analytical expressions for magnetic field, plasma velocity, density and pressure within MCs are derived. These solutions are characterized by conserved values of magnetic flux and helicity. We also investigate the dynamics of self-similarly evolving MCs by means of the numerical code "Graale". In addition, their expansion in a medium with higher density and higher plasma β is studied. It is shown that the physical parameters of the MCs maintain their self-similar character throughout their evolution. Conclusions. A comparison of the different self-similar and numerical solutions allows us to conclude that the evolving MCs are quite adequately described by our self-similar solutions - they retain their self-similar, coherent nature for quite a long time and over large distances from the Sun.
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