arXiv 0908.27752009-08-19physics.space-phphysics.plasm-ph

太阳风湍流等离子体的光谱特征

Spectral features of solar wind turbulent plasma

Dastgeer Shaikh, G. P. Zank

备注：: This paper is accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal
DOI：: 10.1111/j.1365-2966.2009.15579.x

摘要：

利用含时三维霍尔磁流体动力学模拟方法研究了完全可压缩太阳风霍尔磁流体动力学等离子体的光谱特性。我们的模拟，与航天器的数据一致，确定在湍流光谱的特征长度尺度与电磁波动，小于离子gyroradius的光谱断裂。在这个制度中，我们的三维模拟表明，湍流谱级联中存在的平均磁场遵循全向各向异性惯性范围频谱接近$k^{-7/3}$。在我们的模拟中的光谱断裂的发病可以归因于存在的非线性霍尔相互作用，修改的光谱级联。我们的模拟进一步表明，底层characheristic湍流波动是频谱各向异性，其程度严重依赖于当地的波数。与长度尺度小于离子回旋半径的波动是高度可压缩的，并往往表现出在速度和磁场的近均分。最后，我们发现，速度和磁场波动的方向决定了关键的非线性相互作用，主要管理霍尔MHD等离子体，如太阳风的字符。

英文摘要：

Spectral properties of a fully compressible solar wind Hall Magnetohydrodynamic plasma are investigated by means of time dependent three dimensional Hall MHD simulations. Our simulations, in agreement with spacecraft data, identify a spectral break in turbulence spectra at characteristic length-scales associated with electromagnetic fluctuations that are smaller than the ion gyroradius. In this regime, our 3D simulations show that turbulent spectral cascades in the presence of a mean magnetic field follow an omnidirectional anisotropic inertial range spectrum close to $k^{-7/3}$. The onset of the spectral break in our simulations can be ascribed to the presence of nonlinear Hall interactions that modify the spectral cascades. Our simulations further show that the underlying charachteristic turbulent fluctuations are spectrally anisotropic, the extent of which depends critically on the local wavenumber. The fluctuations associated with length scales smaller than the ion gyroradius are highly compressible and tend to exhibit a near equipartition in the velocity and magnetic fields. Finally, we find that the orientation of velocity and magnetic field fluctuations critically determine the character of nonlinear interactions that predominantly govern a Hall MHD plasma, like the solar wind.

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