VELOCITY FIELD OF COMPRESSIBLE MAGNETOHYDRODYNAMIC TURBULENCE: WAVELET DECOMPOSITION AND MODE SCALINGS
VELOCITY FIELD OF COMPRESSIBLE MAGNETOHYDRODYNAMIC TURBULENCE: WAVELET DECOMPOSITION AND MODE SCALINGS
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DOI：
10.1088/0004-637x/720/1/742
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发表时间：
2010-09-01
影响因子：
4.9
通讯作者：
Lazarian, A.
中科院分区：
文献类型：
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作者：
Kowal, Grzegorz;Lazarian, A.
我们研究可压缩磁流体动力学湍流，它持有的许多天体物理过程，包括星星形成和宇宙射线传播的关键。为了解释强湍流流体中磁场的变化，我们使用湍流速度场的小波分解成Alfven，慢，快模式，这是基于傅立叶变换的Cho和Lazarian分解方法的扩展。小波允许我们跟随磁场的局部方向的变化，因此与傅立叶变换相比提高了分解的质量，傅立叶变换是在平均场参考系中完成的。对于每个产生的组件，我们计算的光谱和两点统计，如纵向和横向的结构函数以及更高阶的相干性统计。此外，我们进行了Helmholtz-Hodge分解的速度场不可压缩和可压缩的部分，并分析这些组件。我们发现，不同的组件的湍流的不稳定性是不同的，我们表明，不稳定性统计取决于是否在全球参考框架中的平均磁场或由当地磁场定义的框架中的现象进行了研究。我们得到的措施的依赖性是不同的速度的不同组件，例如，我们表明，虽然阿尔芬模式的不稳定性随马赫数略有变化，快速模式的不稳定性的变化受到很大的影响。
We study compressible magnetohydrodynamic turbulence, which holds the key to many astrophysical processes, including star formation and cosmic-ray propagation. To account for the variations of the magnetic field in the strongly turbulent fluid, we use wavelet decomposition of the turbulent velocity field into Alfven, slow, and fast modes, which presents an extension of the Cho & Lazarian decomposition approach based on Fourier transforms. The wavelets allow us to follow the variations of the local direction of the magnetic field and therefore improve the quality of the decomposition compared to the Fourier transforms, which are done in the mean field reference frame. For each resulting component, we calculate the spectra and two-point statistics such as longitudinal and transverse structure functions as well as higher order intermittency statistics. In addition, we perform a Helmholtz-Hodge decomposition of the velocity field into incompressible and compressible parts and analyze these components. We find that the turbulence intermittency is different for different components, and we show that the intermittency statistics depend on whether the phenomenon was studied in the global reference frame related to the mean magnetic field or in the frame defined by the local magnetic field. The dependencies of the measures we obtained are different for different components of the velocity; for instance, we show that while the Alfven mode intermittency changes marginally with the Mach number, the intermittency of the fast mode is substantially affected by the change.