Evolution of asymmetric multifractal scaling of solar wind turbulence in the outer heliosphere
Evolution of asymmetric multifractal scaling of solar wind turbulence in the outer heliosphere
复制标题
DOI：
10.1029/2008ja013795
复制
发表时间：
2009-03-21
影响因子：
2.8
通讯作者：
Wawrzaszek, Anna
中科院分区：
文献类型：
--
作者：
Macek, Wiesyaw M.;Wawrzaszek, Anna
本研究的目的是研究空间环境中间歇性湍流的标度特性问题。我们分析了旅行者2号航天器在太阳极小期在离太阳不同距离（2.5、25和50 Au）的太阳风速度的时间序列。为了量化太阳风湍流的非对称标度，我们考虑了一个广义的两尺度加权康托集与两个不同的尺度描述不同大小的级联涡旋之间的动能通量的非均匀分布。我们调查所产生的广义维数谱和相应的多重分形奇异谱取决于一个概率测度参数和两个重新标度参数，表明多重分形标度往往是相当不对称的。特别是，我们表明，在太阳极小期的太阳风的多重分形的程度是更大的快流的速度波动比慢流，在太阳极小期的快风可能会表现出很强的非对称标度。此外，我们观察到多重分形标度的太阳风在外层日光层的演变。值得注意的是，对于两个不同的标度参数的模式得到了更好的协议与太阳风的数据，特别是对广义维数的负指数。因此，我们认为，有必要使用一个双尺度级联模型。因此，我们提出这个模型作为一个有用的工具，在各种环境中的间歇性湍流的分析，我们希望我们的新的更一般的非对称多重分形模型可以阐明湍流的性质。
The aim of this study is to examine the question of scaling properties of intermittent turbulence in the space environment. We analyze time series of velocities of the slow and fast speed streams of the solar wind measured in situ by Voyager 2 spacecraft in the outer heliosphere during solar minimum at various distances from the Sun (2.5, 25, and 50 AU). To quantify asymmetric scaling of solar wind turbulence, we consider a generalized two-scale weighted Cantor set with two different scales describing nonuniform distribution of the kinetic energy flux between cascading eddies of various sizes. We investigate the resulting spectrum of generalized dimensions and the corresponding multifractal singularity spectrum depending on one probability measure parameter and two rescaling parameters, demonstrating that the multifractal scaling is often rather asymmetric. In particular, we show that the degree of multifractality for the solar wind during solar minimum is greater for fast streams' velocity fluctuations than that for the slow streams; the fast wind during solar minimum may exhibit strong asymmetric scaling. Moreover, we observe the evolution of multifractal scaling of the solar wind in the outer heliosphere. It is worth noting that for the model with two different scaling parameters a much better agreement with the solar wind data is obtained, especially for the negative index of the generalized dimensions. Therefore, we argue that there is a need to use a two-scale cascade model. Hence, we propose this model as a useful tool for analysis of intermittent turbulence in various environments, and we hope that our new more general asymmetric multifractal model can shed light on the nature of turbulence.