A numerical study of the interplanetary propagation of solar energetic particles with a three-dimensional heliospheric current sheet

Aims . We investigate how solar energetic particles (SEPs) propagate in the interplanetary space that includes the heliospheric current sheet (HCS). We also develop a new model for simulating SEP propagation more realistically and efficiently. Methods . A magnetohydrodynamic (MHD) model was used to simulate the interplanetary background field that includes the HCS and solar wind structures. Additionally, the current sheet was reshaped in the model to reduce the impact of spurious magnetic reconnection in calculation results caused by numerical dissipation. The focused transport equation with a drift-motion term was employed to simulate the transport of SEPs in the interplanetary medium. Results . The model can reproduce the characteristics of the curvature gradient drift of SEPs and the effects of HCS drift that are simulated with the test particle models. The effect of the HCS on the SEPs is significant. It includes an expanded transport range of SEPs in the longitudinal and latitudinal directions and exerts effects on the SEP flux profiles and energy. This numerical model was also used to reproduce a specific event. The HCS and solar wind structures affect the flux rise rate and peak value. The structured solar wind modulates key factors such as the drift velocity, energy evolution, and magnetic connection points, thereby altering the resulting particle flux. As the particle energy decreases, the HCS effect becomes increasingly weaker, whereas the effect of solar wind structures grows stronger. Conclusions . Our model can simulate the SEP propagation near the HCS, based on the guiding center approximation theory. The greatest advantage of our model is that it incorporates the HCS and other interplanetary solar wind structures. For simulations of SEP events, it is crucial to take the roles of the HCS and solar wind structures into account.