THE TRANSPORT OF LOW-FREQUENCY TURBULENCE IN ASTROPHYSICAL FLOWS. I. GOVERNING EQUATIONS
THE TRANSPORT OF LOW-FREQUENCY TURBULENCE IN ASTROPHYSICAL FLOWS. I. GOVERNING EQUATIONS
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DOI：
10.1088/0004-637x/745/1/35
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发表时间：
2012-01
期刊：
影响因子：
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通讯作者：
G. Zank;A. Dosch;P. Hunana;V. Florinski;W. Matthaeus;G. Webb
中科院分区：
文献类型：
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作者：
G. Zank;A. Dosch;P. Hunana;V. Florinski;W. Matthaeus;G. Webb
空间物理学和天体物理学中的许多问题需要详细了解膨胀磁化流中低频湍流的传输和耗散。我们采用尺度分离分解的不可压缩MHD方程（基于Elssässer描述）和发展的时刻层次来描述运输的总能量密度的波动，交叉螺旋度，能量差，和相关长度对应的向前和向后传播模式和能量差。导出了各种输运方程的耗散项。采用单点闭合方案。这项工作的技术要素，区别于以往的研究是（1）包括大规模的背景不均匀阿尔夫维尼奇速度VA在一个比以前更详细的水平，（2）引入一个易于处理的慢时标关闭，以消除高-频率干扰项，对于与非均匀流中湍流输运有关的实际问题，它可能证明是一个有用的近似值如太阳风或日冕，最后，（3）我们开发了一个简化的现象的能量差或等效的剩余能量，可能是有用的实际应用。这产生了一个耦合系统的六个方程，描述了非均匀的亚阿尔夫文和超阿尔夫文流动中的湍流传输。湍流输运方程在空间演化算子中是准线性的，在耗散项中是非线性的，使得模型方程相对易于分析。
Numerous problems in space physics and astrophysics require a detailed understanding of the transport and dissipation of low-frequency turbulence in an expanding magnetized flow. We employ a scale-separated decomposition of the incompressible MHD equations (based on an Elssässer description) and develop a moment hierarchy to describe the transport of the total energy density in fluctuations, the cross-helicity, the energy difference, and correlation lengths corresponding to forward- and backward-propagating modes and to the energy difference. The dissipation terms for the various transport equations are derived. One-point closure schemes are utilized. The technical elements of this work that distinguish it from previous studies are (1) the inclusion of the large-scale background inhomogeneous Alfvénic velocity VA at a level of detail greater than before, (2) the introduction of a tractable slow timescale closure to eliminate high-frequency interference terms that is likely to prove a useful approximation for practical problems related to the transport of turbulence in an inhomogeneous flow such as the solar wind or solar corona, and finally, (3) we develop a simplified phenomenology for the energy difference or equivalently residual energy that may be useful for practical applications. This yields a coupled system of six equations that describes the transport of turbulence in inhomogeneous sub-Alfvénic and super-Alfvénic flows. The turbulence transport equations are quasi-linear in their spatial evolution operators and nonlinear in the dissipation terms, making the model equations relatively tractable to analysis.