Magnetic Turbulence Spectra and Intermittency in the Heliosheath and in the Local Interstellar Medium
Magnetic Turbulence Spectra and Intermittency in the Heliosheath and in the Local Interstellar Medium
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DOI：
10.3847/1538-4357/aafd30
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发表时间：
2019-02-10
影响因子：
4.9
通讯作者：
Tordella, Daniela
中科院分区：
文献类型：
--
作者：
Fraternale, Federico;Pogorelov, Nikolai, V;Tordella, Daniela
对日鞘惯性尺度动力学的理解尚不彻底。这里认为跨内日鞘 (IHS) 和局部星际介质 (LISM) 的磁场波动可以提供 88 至 136 au 之间不同等离子体条件下的准确且高分辨率的统计数据。通过使用航行者星际任务中独特的原位 48 秒测量，我们研究了磁流体动力学 (MHD) 尺度上的不同波动机制，直至 MHD 到动力学的转变。我们关注超过五个频率十进制（5 x 10(-8) < f < 10(-2) Hz）的尺度范围，这在文献分析中是前所未有的。 IHS 中单极区域和扇形区域中八个间隔的一组磁场数据以及 LISM 中四个间隔的磁场数据用于分析。结果以功率谱密度、谱压缩性、结构函数和磁场增量的间歇性的形式给出。在日鞘中，我们识别出表现出类似于 1/f 能量衰减的能量注入状态和惯性级联状态。这里，功率谱是各向异性的，以压缩模式为主，间歇性的峰度值可达10。在星际介质中，湍流结构也是各向异性的，2015年5月后横向波动明显盛行。在这里，我们表明间歇性特征仅出现在小于 10(-6) Hz 的尺度上。
The understanding of inertial-scale dynamics in the heliosheath is not yet thorough. Magnetic field fluctuations across the inner heliosheath (IHS) and the local interstellar medium (LISM) are here considered to provide accurate and highly resolved statistics over different plasma conditions between 88 and 136 au. By using the unique in situ 48 s measurements from the Voyager Interstellar Mission, we investigate different fluctuation regimes at the magnetohydrodynamic (MHD) scales, down to the MHD-to-kinetic transition. We focus on a range of scales exceeding five frequency decades (5 x 10(-8) < f < 10(-2) Hz), which is unprecedented in literature analysis. A set of magnetic field data for eight intervals in the IHS, in both unipolar and sector regions, and four intervals in the LISM is used for the analysis. Results are set forth in terms of the power spectral density, spectral compressibility, structure functions, and intermittency of magnetic field increments. In the heliosheath, we identify the energy-injection regime displaying a similar to 1/f energy decay, and the inertial-cascade regime. Here, the power spectrum is anisotropic and dominated by compressive modes, with intermittency that can reach kurtosis values of up to 10. In the interstellar medium the structure of turbulence is anisotropic as well, with transverse fluctuations clearly prevailing after 2015 May. Here, we show that intermittent features occur only at scales smaller than 10(-6) Hz.