High-speed streams (HSSs) are believed to be only slightly affected by different interactions on their path from the Sun to Earth and thus the analysis of their observations can provide information on the structure and temporal variations of the magnetic field and plasma parameters at the source region. We have chosen three coronal holes supplying 14 HSSs recorded by Wind in 2008. For each HSS, we have calculated the average magnetic field and plasma parameters as well as power spectral densities (PSDs) of magnetic field fluctuations in the MHD and kinetic ranges to investigate their long- and short-term variations. We suggest that long-term variations are connected with a time evolution of the source region on the time scale of solar rotations. On the other hand, the short-term variations would reflect a longitudinal structure of the coronal hole. Our study reveals that coronal holes are very stable source of HSSs and their temporal evolution on short- and long-time scales is negligible. This is true for the average parameters as well as for the fluctuation power and PSDs. Observed correlations between bulk and/or thermal velocity and PSD parameters are consistent with already published results. We suggest that they do not originate in the source region but they can be mostly attributed to interaction with the ambient slow wind that affects even the HSS core.

中文翻译：

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高速流中磁场波动的长期和短期演变

据信，高速流 (HSS) 在从太阳到地球的路径上受到不同相互作用的影响很小，因此对其观测的分析可以提供有关磁场和等离子体参数的结构和时间变化的信息。源区。我们选择了三个冠状孔，提供了 2008 年 Wind 记录的 14 个 HSS。对于每个 HSS，我们计算了平均磁场和等离子体参数以及 MHD 和动力学范围中磁场波动的功率谱密度 (PSD)，以进行研究它们的长期和短期变化。我们认为长期变化与太阳自转时间尺度上源区的时间演化有关。另一方面，短期变化将反映冠状孔的纵向结构。我们的研究表明，日冕洞是 HSS 非常稳定的来源，它们在短期和长期尺度上的时间演变可以忽略不计。对于平均参数以及波动功率和 PSD 都是如此。观察到的体积和/或热速度与 PSD 参数之间的相关性与已发表的结果一致。我们认为它们不是起源于源区，但它们主要归因于与环境慢风的相互作用，甚至影响 HSS 核心。观察到的体积和/或热速度与 PSD 参数之间的相关性与已发表的结果一致。我们认为它们不是起源于源区，但它们主要归因于与甚至影响 HSS 核心的环境慢风的相互作用。观察到的体积和/或热速度与 PSD 参数之间的相关性与已发表的结果一致。我们认为它们不是起源于源区，但它们主要归因于与环境慢风的相互作用，甚至影响 HSS 核心。