Lagrangian Stochastic Model for the Motions of Magnetic Footpoints on the Solar Wind Source Surface and the Path Lengths of Boundary-driven Interplanetary Magnetic Field Lines
Lagrangian Stochastic Model for the Motions of Magnetic Footpoints on the Solar Wind Source Surface and the Path Lengths of Boundary-driven Interplanetary Magnetic Field Lines
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DOI：
10.3847/1538-4357/acbd43
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发表时间：
2023-03
期刊：
影响因子：
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通讯作者：
Gang Li;N. Bian
中科院分区：
文献类型：
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作者：
Gang Li;N. Bian
在这项工作中，我们扩展莱顿的扩散模型描述的湍流混合的磁足点的太阳风源表面。目前的拉格朗日随机模型是基于球面Ornstein-Uhlenbeck过程的漂移，这是由太阳的旋转频率Ω，拉格朗日积分时间尺度τ L，和均方根脚点速度V rms控制。通过对一组随机微分方程的解进行数值求解，得到了太阳风源面上的拉格朗日速度和磁足点的位置。当拉格朗日积分时间尺度趋于零时，Leighton的球形扩散模型在奇异马尔可夫极限下恢复，同时保持足点扩散率有限。与太阳风源表面由标准布朗过程驱动的磁力线不同，在我们的模型中，行星际磁力线是具有有限路径长度的光滑可微函数。数值计算了边界驱动行星际磁力线的路径长度及其在1 Au处的概率分布，并研究了它们与控制参数的关系。的路径长度分布示出开发一个显着的偏度作为分布的宽度增加。
In this work, we extend Leighton’s diffusion model describing the turbulent mixing of magnetic footpoints on the solar wind source surface. The present Lagrangian stochastic model is based on the spherical Ornstein–Uhlenbeck process with drift that is controlled by the rotation frequency Ω of the Sun, the Lagrangian integral timescale τ L, and the root-mean-square footpoint velocity V rms. The Lagrangian velocity and the positions of magnetic footpoints on the solar wind source surface are obtained from the solutions of a set of stochastic differential equations, which are solved numerically. The spherical diffusion model of Leighton is recovered in the singular Markov limit when the Lagrangian integral timescale tends to zero while keeping the footpoint diffusivity finite. In contrast to the magnetic field lines driven by standard Brownian processes on the solar wind source surface, the interplanetary magnetic field lines are smooth differentiable functions with finite path lengths in our model. The path lengths of the boundary-driven interplanetary magnetic field lines and their probability distributions at 1 au are computed numerically, and their dependency with respect to the controlling parameters is investigated. The path-length distributions are shown to develop a significant skewness as the width of the distributions increases.