标题： 太阳活动周期变化下的太阳风湍流复合几何结构 显示英文标题

标题： Solar-cycle Variability of Composite Geometry in the Solar Wind Turbulence

摘要： 太阳风湍流的复合几何结构和谱系各向异性是研究太阳风的重要课题。 在这项工作中，我们使用了从1995年1月到2023年12月期间“风神”号航天器测量的磁场和等离子体数据，该时间段覆盖了两个多太阳活动周期，系统地研究了这些课题在太阳活动周期变化背景下的情况。 所谓的谱比测试和谱各向异性测试被用来确定太阳风湍流的三维（3D）几何结构。 这两种测试都揭示，太阳风湍流主要由二维（2D）分量（约占湍流能量的80%）主导。 更有趣的是，我们发现平板湍流的比例随着太阳黑子数量的增加而增加，平板比例与太阳黑子数量之间的相关系数为0.61（比值测试结果）或0.65（各向异性测试结果）。 这一现象表明，太阳活动的增强（以太阳黑子数量为标志）导致太阳风湍流中的平板成分增加。 讨论并解释了谱系各向异性和太阳活动之间的关系。 平板比例的增加与太阳活动周期上升阶段的行星际磁场强度增强和阿尔芬速度增加有关。 我们的发现将非常有助于更好地理解太阳风湍流的三维复合几何结构及其谱系各向异性，尤其是它们的太阳活动周期变化。 显示英文摘要

摘要： The composite geometry and spectral anisotropy of the solar wind turbulence are very important topics in the investigations of solar wind. In this work, we use the magnetic field and plasma data from Wind spacecraft measured during 1995 January to 2023 December, which covers more than two solar cycles, to systematically investigate these subjects in the context of solar-cycle variability. The so-called spectrum ratio test and spectrum anisotropy test are employed to determine the three-dimensional (3D) geometry of the solar wind turbulence. Both the tests reveal that the solar wind turbulence is dominated by the two-dimensional (2D) component (~80% by turbulence energy). More interestingly, we find that the fraction of slab turbulence increases with the rising sunspot number, and the correlation coefficient between the slab fraction and the sunspot number is 0.61 (ratio test result) or 0.65 (anisotropy test result). This phenomenon suggests that the increasing solar activity (signified by sunspot number) causes increasing slab component in the solar wind turbulence. The relationship between spectral anisotropy and solar activity is discussed and explained. The enhancement of slab fraction is associated with the intensified interplanetary magnetic field magnitude and the increased Alfven speed during the rise phases of the solar cycles. Our findings will be very helpful for achieving a better understanding of the 3D composite geometry and spectral anisotropy of the solar wind turbulence, and especially of their solar-cycle variability.