从太阳风磁场涨落在动力学尺度上的标度特性推导广义Kappa分布
Derivation of generalized Kappa distribution from scaling properties of solar wind magnetic field fluctuations at kinetic scales
AI总结：
本文通过尺度依赖Langevin方程解析推导出描述太阳风动力学尺度磁场涨落统计的主曲线，该主曲线是含尾部与不对称性双参数的广义Kappa分布，并经Parker Solar Probe和Cluster观测数据验证至5σ以上。
摘要：
弱碰撞空间等离子体中的动力学尺度动力学通常表现出磁场涨落的自相似统计特性，这意味着存在一个不变的概率密度函数（主曲线）。我们通过假设垂直涨落可以通过一个依赖于尺度的Langevin方程来建模，提供了该主曲线的解析推导。在我们的模型中，磁场涨落是随机变量，其尺度间的演化被假定为一个Langevin过程。我们提出了一个描述动力学尺度涨落统计特性的主曲线的形式化推导。模型预测在帕克太阳探测器（Parker Solar Probe）在太阳附近和Cluster在地球附近测量的快速太阳风独立数据样本上进行了检验。该主曲线是Kappa分布的推广，具有两个参数：一个调节尾部，另一个控制不对称性。模型预测与航天器观测结果在垂直磁场涨落情况下匹配到5σ甚至更高。
英文摘要：
Kinetic scale dynamics in weakly-collisional space plasmas usually exhibits a self-similar statistics of magnetic field fluctuations which implies the existence of an invariant probability density function (master curve). We provide an analytical derivation of the master curve by assuming that perpendicular fluctuations can be modeled through a scale-dependent Langevin equation. In our model, magnetic field fluctuations are the stochastic variable and their scale-to-scale evolution is assumed to be a Langevin process. We propose a formal derivation of the master curve describing the statistics of the fluctuations at kinetic scales. Model predictions are tested on independent data samples of fast solar wind measured near the Sun by Parker Solar Probe and near the Earth by Cluster. The master curve is a generalization of the Kappa distribution with two parameters: one regulating the tails and the other one controlling the asymmetry. Model predictions match the spacecraft observations up to 5$σ$ and even beyond in the case of perpendicular magnetic field fluctuations.
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