Cosmic ray fluctuations and MHD waves in the solar wind

Pub Date : 2023-06-29 DOI:10.12737/stp-92202309
Sergei Starodubtsev, Anton Zverev, Peter Gololobov, Vladislav Grigoryev
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Abstract

During large-scale solar wind disturbances, variations in galactic cosmic rays with periods from several minutes to 2–3 hours, which are called cosmic ray fluctuations in the scientific literature, often occur. Such fluctuations are not observed in the absence of disturbances. Since cosmic rays are charged particles, their modulation in the heliosphere occurs mainly under the influence of the interplanetary magnetic field, or rather its turbulent part — MHD waves. In order to adequately describe the relationship between their fluctuation spectra, it is necessary to be able to isolate a certain type of MHD waves from direct measurements of the interplanetary medium parameters. In this paper, we consider some methods for determining the contribution of three solar wind MHD turbulence branches, namely, Alfvén, fast, and slow magnetosonic waves corresponding to the turbulence spectrum inertial region frequencies 10⁻⁴<ν<10⁻¹ Hz, at which cosmic ray fluctuations are observed, to the observed power spectra of interplanetary magnetic field modulus fluctuations. To do this, we apply the methods of spectral and polarization analysis. In the absence of measurement data on SW parameters, to identify the type of MHD turbulence we use the known wave polarization properties that Alfvén and magnetosonic waves are polarized in different planes relative to the plane containing the average IMF vector and wave vector. Our results show that with the correct determination of the spectra of three MHD wave types, their sum, within the limits of errors, agrees well with the observed spectra of the interplanetary magnetic field modulus, and a small difference can be attributed to static inhomogeneities and oscillations frozen into plasma, as well as to various discontinuities that are always inevitably present in the solar wind.
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宇宙射线波动和太阳风中的MHD波
在大规模太阳风扰动期间,银河宇宙射线的变化周期从几分钟到2-3小时不等,在科学文献中称为宇宙射线波动。这种波动在没有扰动的情况下是观察不到的。由于宇宙射线是带电粒子,它们在日球层中的调制主要是在行星际磁场的影响下发生的,或者更确切地说,是在行星际磁场的湍流部分——MHD波的影响下发生的。为了充分描述它们的涨落谱之间的关系,必须能够从行星际介质参数的直接测量中分离出某种类型的MHD波。在本文中,我们考虑了一些方法来确定三个太阳风MHD湍流分支,即与湍流谱惯性区频率10⁻⁴<ν<10⁻¹Hz相对应的alfv,快速和慢磁声波对观测到的行星际磁场模量波动的功率谱的贡献。为此,我们采用了光谱和偏振分析的方法。在没有SW参数测量数据的情况下,为了识别MHD湍流的类型,我们使用了已知的波极化特性,即相对于包含平均IMF矢量和波矢量的平面,alfv和磁声波在不同的平面上极化。 我们的研究结果表明,在正确确定三种MHD波类型的光谱后,它们的总和在误差范围内与观测到的行星际磁场模量光谱非常吻合,而微小的差异可归因于静态不均匀性和冻结在等离子体中的振荡,以及太阳风中不可避免地存在的各种不连续。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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