The Diffusion Tensor of Protons at 1au: Comparing Simulation, Observation, andTheory

Abstract

The natural variation in plasma parameters observed at 1 au can lead to a variation in transport parameters, such asdiffusion and drift coefficients, for energetic charged particles of solar and galactic origin. Given the importance ofthese parameters to particle transport studies, this variation is investigated through test particle simulations over arange of energies in the presence of simulated turbulence with properties corresponding to an ensemble of observedturbulence conditions at Earth. The resulting transport coefficients are then compared with observational estimatesfrom the literature, as well as the predictions of several scattering theories. Parallel and perpendicular meanfree paths are shown to vary widely, for the former in agreement with prior observational estimates, but not for thelatter. Furthermore, a large disparity between the predictions of theory and the simulation results is noted for theperpendicular mean free path. As such, these results indicate that particle transport studies, particularly predictiveones, need to take into account this natural variation in transport coefficients