Heliospheric Diffusion of Stochastic Parker Spirals in Radially Evolving Solar Wind Turbulence
Heliospheric Diffusion of Stochastic Parker Spirals in Radially Evolving Solar Wind Turbulence
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DOI：
10.3847/1538-4357/ad19dd
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发表时间：
2024-02
期刊：
影响因子：
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通讯作者：
N. Bian;R. D. Strauss;G. Li;N. E. Engelbrecht
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文献类型：
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作者：
N. Bian;R. D. Strauss;G. Li;N. E. Engelbrecht
我们提出了一个随机场线映射模型，其中行星际磁力线用密度分布函数来描述，该密度分布函数满足数值求解的Fokker-Planck方程。由于标称帕克场的螺旋几何和太阳风湍流的演化性质，日球层磁力线的扩散既是不均匀的，又是各向异性的，包括一个径向分量。磁力线的纵向分布接近于圆形高斯分布，但它们具有明显的偏斜性。研究发现，从太阳发出的磁力线与帕克预测的螺旋线平均不同。尽管螺旋线仍然接近阿基米德，但平均而言，它们在这里处于低谷。我们的模型预测了在相同的太阳风速为Vsw=40 0 km S∼1的情况下，地球轨道上的螺旋角比地球轨道上的帕克螺旋角小5°。它还预测了太阳圆盘上最佳磁连接足点的角度位置，该位置相对于帕克场模型向西移动了∼10°。这极大地改变了太阳上可能的源和内日光层的观测者之间最可能的磁连接的角度。这一结果对太阳喷发后加速的“无散射”电子在日球层的传输有直接的影响。
We present a stochastic field line mapping model where the interplanetary magnetic field lines are described by a density distribution function satisfying a Fokker–Planck equation that is solved numerically. Due to the spiral geometry of the nominal Parker field and to the evolving nature of solar wind turbulence, the heliospheric diffusion of the magnetic field lines is both heterogeneous and anisotropic, including a radial component. The longitudinal distributions of the magnetic field lines are shown to be close to circular Gaussian distributions, although they develop a noticeable skewness. The magnetic field lines emanating from the Sun are found to differ, on average, from the spirals predicted by Parker. Although the spirals remain close to Archimedean, they are here underwound, on average. Our model predicts a spiral angle that is smaller by ∼5° than the Parker spiral angle at Earth’s orbit for the same solar wind speed of V sw = 400 km s−1. It also predicts an angular position on the solar disk of the best magnetically connected footpoint to an observer at 1 au that is shifted westward by ∼10° with respect to the Parker’s field model. This significantly changes the angle of the most probable magnetic connection between possible sources on the Sun and observers in the inner heliosphere. The results have direct implications for the heliospheric transport of “scatter-free” electrons accelerated in the aftermath of solar eruptions.