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arXiv 1202.6010astro-ph.SR
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大尺度起伏磁场中太阳高能粒子的跨场输运

Cross-Field Transport of Solar Energetic Particles in a Large-Scale Fluctuating Magnetic Field

James Kelly, Silvia Dalla, Timo Laitinen

摘要:

利用全轨道粒子模拟程序,模拟了太阳高能粒子(SEP)在行星际磁场(IMF)中的运动轨迹.粒子在三种传播条件(无散射,散射平均自由程λ =0.3 AU和λ =2 AU)下经历的交叉场传输的特征在于Parker螺旋几何形状。在从模拟输出计算粒子位移和扩散系数时,考虑了磁场随太阳径向距离的膨胀的作用。据发现,跨磁场的运输是增强在λ =0.3 AU和λ =2 AU的情况下,相比于无散射的情况下。垂直扩散系数与平行扩散系数的比值在0.01和0.08之间变化。垂直于磁场的纬向与纵向扩散系数之比通常为0.2,表明在纬向的传输效率可能较低。

英文摘要:

The trajectories of Solar Energetic Particles (SEPs) in an Interplanetary Magnetic Field (IMF) exhibiting large-scale fluctuations due to footpoint motions originating in the photosphere, are simulated using a full-orbit test-particle code. The cross-field transport experienced by the particles in three propagation conditions (scatter-free, with scattering mean free path lambda=0.3 AU and lambda=2 AU) is characterized in the Parker spiral geometry. The role of expansion of the magnetic field with radial distance from the Sun is taken into consideration in the calculation of particle displacements and diffusion coefficients from the output of the simulations. It is found that transport across the magnetic field is enhanced in the lambda=0.3 AU and lambda=2 AU cases, compared to the scatter-free case. Values of the ratios of perpendicular to parallel diffusion coefficients vary between 0.01 and 0.08. The ratio of latitudinal to longitudinal diffusion coefficient perpendicular to the magnetic field is typically 0.2, suggesting that transport in latitude may be less efficient.

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