标题： 太阳风和MHD湍流中的磁不连续分布 显示英文标题

标题： Distribution of Magnetic Discontinuities in the Solar Wind and in MHD Turbulence

摘要： 通过测量磁场方向的波动来研究太阳风中磁不连续性的统计特性，这些波动由磁矢量在时间间隔Δt内发生的旋转Δθ给出。我们表明，旋转的概率密度函数P(Δθ)可以用一个简单的模型来描述，在该模型中，磁矢量以相对增量（ΔB）/B的形式旋转，且（ΔB）/B服从对数正态分布。 我们发现增量的概率密度函数P((ΔB)/B)具有显著的标度性质：对于所有时间间隔Δt，归一化变量x=[(ΔB)/B]*[(Δt)/(Δt_0)]^-a都具有通用的对数正态分布。然后我们将太阳风的测量结果与磁流体动力学（MHD）湍流的直接数值模拟结果进行比较。 当选择适当的磁场引导场与波动比B_0/b_rms时，两种情况下得到的P(Δθ)有良好的一致性。然而，在惯性区间相对较短的MHD模拟中，P((ΔB)/B)的尺度不变性被破坏，这导致P(Δθ)随测量区间的变化方式与太阳风中的不同。 显示英文摘要

摘要： The statistical properties of magnetic discontinuities in the solar wind are investigated by measuring fluctuations in the magnetic field direction, given by the rotation Delta theta that the magnetic field vector undergoes during time interval Delta t. We show that the probability density function for rotations, P(Delta theta), can be described by a simple model in which the magnetic field vector rotates with a relative increment (Delta B)/B that is lognormally distributed. We find that the probability density function of increments, P((Delta B)/B), has a remarkable scaling property: the normalized variable x=[(Delta B)/B]*[(Delta t)/(Delta t_0)]^-a has a universal lognormal distribution for all time intervals Delta t. We then compare measurements from the solar wind with those from direct numerical simulations of magnetohydrodynamic (MHD) turbulence. We find good agreement for P(Delta theta) obtained in the two cases when the magnetic guide-field to fluctuations ratio B_0/b_rms is chosen accordingly. However, the scale invariance of P((Delta B)/B) is broken in the MHD simulations with relatively limited inertial interval, which causes P(Delta theta) to scale with measurement interval differently than in the solar wind.