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arXiv 2012.00811astro-ph.SR
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低层非均匀太阳风的三维模拟

Three-dimensional simulations of the inhomogeneous Low Solar Wind

N. Magyar, V. M. Nakariakov

摘要:

在不久的将来,帕克太阳探测器将对日冕和太阳风之间的动力学和性质的理论进行严格的测试。磁流体动力学(MHD)湍流是解释新生太阳风动力学(包括加热和加速)的最流行的机制。以往的模型大多关注于由出射Alfvén波及其反射波相互作用引起的非线性级联效应,而忽略了可能与日冕等离子体垂直结构有关的效应,尽管有大量的证据支持这一点.本文首次通过三维MHD数值模拟分析了垂直结构的日冕和太阳风的动力学,从低日冕到15 R_Sun。我们发现,背景结构的演变MHD湍流有很强的影响,在更快的时间尺度比垂直均匀的情况下。在比非线性时间短的时间尺度上,与相位混合相关的线性效应导致1/f垂直能谱。随着湍流级联的发展,我们观察到一个垂直(平行)的能量谱,其幂律指数为-3/2或-5/3(-2),一个比速度谱更陡的垂直磁场,以及一个强烈的负剩余能量的积累。我们的结论是,湍流是最有可能产生的驱动横向扭结波的自级联,以前被称为“uniturbulence”,这可能是占主导地位的非线性能量级联通道中的原始太阳风。

英文摘要:

In the near future, Parker Solar Probe will put theories about the dynamics and nature of the transition between the solar corona and the solar wind to stringent tests. The most popular mechanism aimed to explain the dynamics of the nascent solar wind, including its heating and acceleration is magnetohydrodynamic (MHD) turbulence. Most of the previous models focus on nonlinear cascade induced by interactions of outgoing Alfvén waves and their reflections, ignoring effects that might be related to perpendicular structuring of the solar coronal plasma, despite overwhelming evidence for it. In this paper, for the first time, we analyse through 3D MHD numerical simulations the dynamics of the perpendicularly structured solar corona and solar wind, from the low corona to 15 R_Sun. We find that background structuring has a strong effect on the evolution of MHD turbulence, on much faster time scales than in the perpendicularly homogeneous case. On time scales shorter than nonlinear times, linear effects related to phase mixing result in a 1/f perpendicular energy spectrum. As the turbulent cascade develops, we observe a perpendicular (parallel) energy spectrum with the power law index of -3/2 or -5/3 (-2), a steeper perpendicular magnetic field than velocity spectrum, and a strong build-up of negative residual energy. We conclude that the turbulence is most probably generated by the self-cascade of the driven transverse kink waves, referred to previously as `uniturbulence', which might represent the dominant nonlinear energy cascade channel in the pristine solar wind.

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