Progress in Simulations of Solar Energetic Particles (SEPs) Propagation in Large-Scale Structures of Interplanetary Background Solar Wind

Solar energetic particle (SEP) events, driven by solar flares or coronal mass ejections (CMEs), generate high-energy particles (ranging from keV to GeV) that pose significant threats to spacecraft, astronauts, and Earth's space environment. As human space activities expand, predicting and mitigating SEP events has become a critical task in space weather forecasting. The propagation of SEPs in interplanetary space is strongly modulated by large-scale solar wind structures, particularly Stream Interaction Regions (SIRs). To improve SEP prediction accuracy, research teams have employed multiple solar wind models --- including Parker-like analytical solutions, satellite-observation-driven frameworks, and three-dimensional (3D) magnetohydrodynamic (MHD) simulations --- coupled with SEP transport models based on the focused transport equation. Simulations reveal that magnetic focusing effects dominate flux enhancements in compression regions, while adiabatic cooling in fast solar wind significantly accelerates particle energy decay. The width of corotating interaction regions (CIRs) is closely linked to solar wind speed, tilt angle, and fast-stream azimuthal extent, modulating particle acceleration efficiency and spatiotemporal intensity profiles. Incorporating perpendicular diffusion into data-driven models refines the characterization of SIR-associated SEP events, explaining flux profile discrepancies across observational locations. While a theoretical framework linking large-scale solar wind structures to SEP propagation has been established, future work would integrate high-resolution observations with multi-parameter models to enhance simulations of CME-driven shocks and improve the precision of particle transport descriptions.