Statistics of solar wind electron breakpoint energies using machine learning techniques
Statistics of solar wind electron breakpoint energies using machine learning techniques
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DOI：
10.1051/0004-6361/202037840
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发表时间：
2020-05
影响因子：
6.5
通讯作者：
M. Bakrania;I. J. Rae;A. Walsh;D. Verscharen;Andy W. Smith;T. Bloch;C. Watt
中科院分区：
文献类型：
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作者：
M. Bakrania;I. J. Rae;A. Walsh;D. Verscharen;Andy W. Smith;T. Bloch;C. Watt
太阳风电子速度在1Au的分布由一个热“核”群和两个超热群组成：“晕”和“Strahl”。核心和晕是准各向同性的，而Strahl通常沿行星际磁场的平行或反平行方向向外径向传播。使用星团和平数据，我们分析了能量和俯仰角分布，并使用机器学习技术来提供这些太阳风种群的可靠分类。最初，我们使用非监督算法对HALO和Strahl微分能流分布进行分类，以允许我们计算相对数密度，这些密度与以前的结果具有相同的数量级。随后，我们将非监督算法应用于十年来的相空间密度分布，研究了晕和Strahl断点能量随太阳风参数的变化。在我们的统计研究中，我们发现晕和Strahl超热断裂能都随着核温度的升高而显著增加，其中晕比Strahl表现出更大的正相关性。我们得出的结论是，低能Strahl电子以垂直的俯仰角散射到核心。这增加了库仑碰撞的次数，并将垂直的核布居扩展到更高的能量，导致在更高的核温度下，晕和Strahl断点能量之间的差异更大。从统计上看，这两个超热断点能量的位置都随着太阳风速的增加而减少。在晕断点能量的情况下，我们观测到了S−1上方和下方的两个截然不同的轮廓，这与快太阳风和慢太阳风的起源不同有关。
Solar wind electron velocity distributions at 1 au consist of a thermal “core” population and two suprathermal populations: “halo” and “strahl”. The core and halo are quasi-isotropic, whereas the strahl typically travels radially outwards along the parallel or anti-parallel direction with respect to the interplanetary magnetic field. Using Cluster-PEACE data, we analyse energy and pitch angle distributions and use machine learning techniques to provide robust classifications of these solar wind populations. Initially, we used unsupervised algorithms to classify halo and strahl differential energy flux distributions to allow us to calculate relative number densities, which are of the same order as previous results. Subsequently, we applied unsupervised algorithms to phase space density distributions over ten years to study the variation of halo and strahl breakpoint energies with solar wind parameters. In our statistical study, we find both halo and strahl suprathermal breakpoint energies display a significant increase with core temperature, with the halo exhibiting a more positive correlation than the strahl. We conclude low energy strahl electrons are scattering into the core at perpendicular pitch angles. This increases the number of Coulomb collisions and extends the perpendicular core population to higher energies, resulting in a larger difference between halo and strahl breakpoint energies at higher core temperatures. Statistically, the locations of both suprathermal breakpoint energies decrease with increasing solar wind speed. In the case of halo breakpoint energy, we observe two distinct profiles above and below 500 km s−1. We relate this to the difference in origin of fast and slow solar wind.