Progress in Simulations of Solar Energetic Particles Propagation in Large-scale Structures of Interplanetary Background Solar Wind

Abstract

Solar energetic particle (SEP) events, driven by solar flares or coronal mass ejections (CMEs), can rapidly produce particles with energies from a few keV to several GeV. Their propagation is strongly modulated by the large-scale structure of the solar wind, posing risks to spacecraft operations and making SEPs a central target of space weather forecasting. In this work, we simulate SEP events by coupling the focused transport equation with multiple background solar wind models, perform a detailed parameter study, and reproduce several SEP events associated with stream interaction regions (SIRs) using observational constraints. Our results demonstrate that magnetic focusing is the dominant mechanism responsible for flux enhancement, whereas adiabatic cooling governs the decay phase in fast solar wind environments. Variations in solar wind parameters modify the width of corotating interaction regions (CIRs), which in turn lead to pronounced spatiotemporal variations in particle transport. Incorporating perpendicular diffusion effectively reconciles discrepancies among multi spacecraft flux profiles. This study establishes a comprehensive framework for understanding how large scale solar wind structures modulate SEP propagation. Future work should integrate multi mission observations to better capture CME driven shocks and thereby improve predictive capabilities for energetic particle transport.