Propagation of Scatter-free Solar Energetic Electrons in a Meandering Interplanetary Magnetic Field

We investigate energetic electron transport in a meandering interplanetary magnetic field under the scatter-free regime. The meandering magnetic field is adopted from the Giacalone model in which a single parameter V _rms is used to characterize how the interplanetary magnetic field deviates from the Parker field. The trajectories of energetic electrons are followed in this meandering field using test particle simulations. Ten thousand electrons are injected in the ecliptic plane and the path length distributions are obtained at distances 0.2, 0.5, 1.0, 2.0, and 3.0 au from the Sun for five different V _rms, 0.3, 0.6, 1.0, 1.5, 2.0, and 2.5 km s^-1. By generating 10,000 different realizations of the meandering field line, we also obtain the path length distribution of the field lines. Our simulations show that the path length distributions of the electrons and that of the field lines are different and the difference increases with V _rms. When the V _rms approaches zero, the field lines approach the Parker field, and the differences between particle path lengths and field path lengths are small but nonzero due to the gradient and curvature drifts. The path lengths for 1 MeV electrons do not differ much from those for 100 MeV electrons. Our results of the distribution of electron path length can be compared to the observations of Zhao et al. to set constraints on V _rms. We also calculate both the longitudinal and latitudinal displacements from the source when electrons arrive at 1 au. This provides some basis for understanding simultaneous observations of impulsive events made at multiple spacecraft.