Modeling energetic proton transport in a corotating interaction region

Abstract

Aims. An energetic particle event related to a corotating interaction region (CIR) structure was observed by the Solar-Terrestrial Relations Observatory-A (STEREO-A) from 21 to 24 August 2016. Based on an analysis of measurement data, we suggest that instead of being accelerated by distant shocks, a local mechanism similar to diffusive shock acceleration (DSA) acting in the compression region could explain the flux enhancements of 1.8–10.0 MeV nucleon−1 protons. We created simulations to verify our hypothesis. Methods. We developed a coupled model composed of a data-driven analytical background model providing solar wind configuration and a particle transport model represented by the focused transport equation (FTE). We simulated particle transport in the CIR region of interest in order to obtain the evolution of proton fluxes and derive the spectra. Results. We find that the simulation is well correlated with the observation. The mechanism of particle scattering back and forth between the trap-like structure of interplanetary magnetic field (IMF) in the compression region is the major factor responsible for the flux enhancements in this energetic particle event, and perpendicular diffusion identified by a ratio of κ⊥/κ|| ∼ 10−2 plays an important role in the temporal evolution of proton fluxes.