Multispacecraft Analysis of the Properties of Magnetohydrodynamic Fluctuations in Sub-Alfvénic Solar Wind Turbulence at 1 au
Multispacecraft Analysis of the Properties of Magnetohydrodynamic Fluctuations in Sub-Alfvénic Solar Wind Turbulence at 1 au
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1 天文亚亚芬尼太阳风湍流中磁流体动力脉动特性的多航天器分析
DOI：
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发表时间：
2022
影响因子：
4.9
通讯作者：
Huizi Wang
中科院分区：
文献类型：
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作者：
S. Q. Zhao;Huirong Yan;T. Liu;Mingzhe Liu;Huizi Wang
利用磁层多尺度探测器观测了波矢空间的三维磁功率谱，研究了磁流体动力学（MHD）尺度下亚Alfvénic太阳风湍流的各向异性和尺度变化。在傅立叶空间中，将磁功率分布组织在由波矢（κ ε）和背景磁场（b^0）确定的新坐标中。本研究利用两种方法来确定波矢量：奇异值分解方法和多航天器时序分析。这两种方法的组合允许检查的磁场波动的模式组成方面的属性，而没有任何时空假设。观测表明，在垂直于κ ε和b^0的方向上的涨落（δ B 1）显著地垂直于b^0级联，并且这种各向异性随着波数的增加而增加。δ B <$1的约化功率谱遵循Goldreich-Sridhar标度：P <$（k <$）<$k <$−5/3和P <$（k <$）<$k <$−2。与此相反，在k b 0平面内的波动表现出各向同性的行为：垂直的功率分布是近似相同的平行分布。在k B 0平面内的涨落的约化功率谱遵循标度P（k）−3/2和P（k −3/2。将频率-波矢谱与MHD模的理论色散关系进行比较，发现δ B 1很可能与Alfvén模有关。另一方面，磁场波动内的k b 0平面更可能源于快速模式的基础上，他们的各向同性行为。观测到的各向异性和不同磁场分量的标度与当前可压缩MHD理论的预测是一致的。此外，对于Alfvénic组件，级联时间的比值波周期被发现是一个因素的几个，在强湍流状态下的临界平衡一致。这些结果对进一步研究等离子体湍流的能量组成及其对高能粒子输运的影响具有参考价值。
We present observations of three-dimensional magnetic power spectra in wavevector space to investigate the anisotropy and scalings of sub-Alfvénic solar wind turbulence at magnetohydrodynamic (MHD) scale using the Magnetospheric Multiscale spacecraft. The magnetic power distributions are organized in a new coordinate determined by wavevectors ( κˆ ) and background magnetic field ( b^0 ) in Fourier space. This study utilizes two approaches to determine wavevectors: the singular value decomposition method and multispacecraft timing analysis. The combination of the two methods allows an examination of the properties of magnetic field fluctuations in terms of mode compositions without any spatiotemporal hypothesis. Observations show that fluctuations (δ B ⊥1) in the direction perpendicular to κˆ and b^0 prominently cascade perpendicular to b^0 , and such anisotropy increases with wavenumbers. The reduced power spectra of δ B ⊥1 follow Goldreich–Sridhar scalings: Pˆ(k⊥)∝k⊥−5/3 and Pˆ(k∥)∝k∥−2 . In contrast, fluctuations within the kˆbˆ0 plane show isotropic behaviors: perpendicular power distributions are approximately the same as parallel distributions. The reduced power spectra of fluctuations within the kˆbˆ0 plane follow the scalings Pˆ(k⊥)∝k⊥−3/2 and Pˆ(k∥)∝k∥−3/2 . Comparing frequency–wavevector spectra with theoretical dispersion relations of MHD modes, we find that δ B ⊥1 are probably associated with Alfvén modes. On the other hand, magnetic field fluctuations within the kˆbˆ0 plane more likely originate from fast modes based on their isotropic behaviors. The observations of anisotropy and scalings of different magnetic field components are consistent with the predictions of current compressible MHD theory. Moreover, for the Alfvénic component, the ratio of cascading time to the wave period is found to be a factor of a few, consistent with critical balance in the strong turbulence regime. These results are valuable for further studies of energy compositions of plasma turbulence and their effects on energetic particle transport.