Hnat Bogdan, Chapman Sandra C, Rowlands George
Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 May;67(5 Pt 2):056404. doi: 10.1103/PhysRevE.67.056404. Epub 2003 May 21.
The solar wind provides a natural laboratory for observations of magnetohydrodynamic (MHD) turbulence over extended temporal scales. Here, we apply a model independent method of differencing and rescaling to identify self-similarity in the probability density functions (PDF) of fluctuations in solar wind bulk plasma parameters as seen by the WIND spacecraft. Whereas the fluctuations of speed v and interplanetary magnetic field (IMF) magnitude B are multifractal, we find that the fluctuations in the ion density rho, energy densities B2 and rhov(2) as well as MHD-approximated Poynting flux vB(2) are monoscaling on the time scales up to 26 hr. The single curve, which we find to describe the fluctuations PDF of all these quantities up to this time scale, is non-Gaussian. We model this PDF with two approaches--Fokker-Planck, for which we derive the transport coefficients and associated Langevin equation, and the Castaing distribution that arises from a model for the intermittent turbulent cascade.
太阳风为在扩展时间尺度上观测磁流体动力学（MHD）湍流提供了一个自然实验室。在此，我们应用一种与模型无关的差分和重标度方法，来识别WIND航天器观测到的太阳风整体等离子体参数波动的概率密度函数（PDF）中的自相似性。虽然速度v和行星际磁场（IMF）大小B的波动是多重分形的，但我们发现离子密度ρ、能量密度B²和ρv²以及MHD近似的坡印廷通量vB²的波动在长达26小时的时间尺度上是单标度的。我们发现，在这个时间尺度之前，描述所有这些量的波动PDF的单一曲线是非高斯的。我们用两种方法对这个PDF进行建模——福克 - 普朗克方法，我们从中推导传输系数和相关的朗之万方程，以及由间歇性湍流级联模型产生的卡斯廷分布。
