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We introduce a new solar energetic particle (SEP) transport code that aims atstudying the effects of different solar wind configurations on SEP events. Wefocus on the influence of varying solar wind velocities on the energy changesof SEPs, and study how a non-Parker background solar wind can trap particlestemporarily at small heliocentric radial distances (r<1.5 AU). Our modelcomputes particle distributions by solving the focused transport equation (FTE)in a stochastic manner by propagating particles in a solar wind generated bythe heliospheric MHD model EUHFORIA. We solve the FTE, including all solar windeffects and cross-field diffusion. As initial conditions, we inject 4 MeVprotons impulsively, and spread uniformly over a selected region at the innerboundary of the model. To verify the model, we first assume nominal undisturbedfast and slow solar winds. Thereafter, we analyse the propagation of particlesin a solar wind containing a corotating interaction region (CIR). Theintensity-time profiles obtained in the simulations using the nominal solarwinds illustrate the considerable adiabatic deceleration undergone by SEPs whenpropagating in a fast solar wind. For the solar wind containing a CIR, weobserve particles accelerating when propagating in the compression and shockwaves bounding the CIR. These waves and the magnetic configuration near thestream interface also act as a magnetic mirror, producing long-lasting highintensities at small radial distances. We also illustrate how the efficiency ofthe cross-field diffusion in the heliosphere is altered due to compressedmagnetic fields. Finally, cross-field diffusion enables some particles to reachthe forward shock wave, resulting in the formation of an accelerated particlepopulation centred on the forward shock, despite the lack of magneticconnection between the particle injection region and this shock wave.

Modelling three-dimensional transport of solar energetic protons in a corotating interaction region generated with EUHFORIA