Abstract. In this work, we investigate magnetic field fluctuations in three coronal mass ejection (CME)-driven sheath regions at 1 AU, with their speeds ranging from slow to fast. The data set we use consists primarily of high-resolution (0.092 s) magnetic field measurements from the Wind spacecraft. We analyse magnetic field fluctuation amplitudes, compressibility, and spectral properties of fluctuations. We also analyse intermittency using various approaches; we apply the partial variance of increments (PVIs) method, investigate probability distribution functions of fluctuations, including their skewness and kurtosis, and perform a structure function analysis. Our analysis is conducted separately for three different subregions within the sheath and one in the solar wind ahead of it, each 1 h in duration. We find that, for all cases, the transition from the solar wind ahead to the sheath generates new fluctuations, and the intermittency and compressibility increase, while the region closest to the ejecta leading edge resembled the solar wind ahead. The spectral indices exhibit large variability in different parts of the sheath but are typically steeper than Kolmogorov's in the inertial range. The structure function analysis produced generally the best fit with the extended p model, suggesting that turbulence is not fully developed in CME sheaths near Earth's orbit. Both Kraichnan–Iroshinikov and Kolmogorov's forms yielded high intermittency but different spectral slopes, thus questioning how well these models can describe turbulence in sheaths. At the smallest timescales investigated, the spectral indices indicate shallower than expected slopes in the dissipation range (between −2 and −2.5 ), suggesting that, in CME-driven sheaths at 1 AU, the energy cascade from larger to smaller scales could still be ongoing through the ion scale. Many turbulent properties of sheaths (e.g. spectral indices and compressibility) resemble those of the slow wind rather than the fast. They are also partly similar to properties reported in the terrestrial magnetosheath, in particular regarding their intermittency, compressibility, and absence of Kolmogorov's type turbulence. Our study also reveals that turbulent properties can vary considerably within the sheath. This was particularly the case for the fast sheath behind the strong and quasi-parallel shock, including a small, coherent structure embedded close to its midpoint. Our results support the view of the complex formation of the sheath and different physical mechanisms playing a role in generating fluctuations in them.

中文翻译：

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近地太阳风日冕物质抛射驱动鞘区的磁场波动特性

摘要。在这项工作中，我们研究了 1 AU 处三个日冕物质抛射 (CME) 驱动的鞘区的磁场波动，它们的速度从慢到快。我们使用的数据集主要包括来自 Wind 航天器的高分辨率 (0.092 s) 磁场测量值。我们分析了磁场波动幅度、可压缩性和波动的频谱特性。我们还使用各种方法分析间歇性；我们应用增量的偏方差 (PVI) 方法，研究波动的概率分布函数，包括它们的偏度和峰度，并进行结构函数分析。我们的分析分别针对鞘内的三个不同子区域和一个在它前面的太阳风中进行，每个区域持续 1 小时。我们发现，对于所有情况，从前方的太阳风到鞘层的过渡产生了新的波动，间歇性和可压缩性增加，而最靠近喷射物前缘的区域类似于前方的太阳风。光谱指数在护套的不同部分表现出很大的可变性，但在惯性范围内通常比 Kolmogorov 的更陡峭。结构函数分析通常与扩展 p 模型产生最佳拟合，表明在地球轨道附近的 CME 鞘层中湍流并未完全发展。Kraichnan-Iroshinikov 和 Kolmogorov 的形式都产生了高间歇性但不同的光谱斜率，因此质疑这些模型可以如何描述鞘中的湍流。在调查的最小时间尺度上，光谱指数表明耗散范围内（-2 和 -2.5 之间）的斜率比预期的更浅，这表明，在 1 AU 的 CME 驱动的鞘中，从较大到较小尺度的能量级联仍然可以通过离子尺度进行。护套的许多湍流特性（例如光谱指数和可压缩性）类似于慢风而不是快风。它们也部分地类似于在地球磁鞘中报告的特性，特别是在它们的间歇性、可压缩性和不存在 Kolmogorov 型湍流方面。我们的研究还表明，护套内的湍流特性可能会有很大差异。强烈和准平行冲击背后的快速鞘尤其如此，包括一个嵌入其中点附近的小而连贯的结构。