  We study how a high-speed solar wind stream embedded in a slow solar wind
affects the transport and energy changes of solar energetic protons in
interplanetary space, assuming different levels of cross-field diffusion. This
is done using a particle transport model that computes directional particle
intensities and first order parallel anisotropies in a background solar wind
generated by the magnetohydrodynamic model EUHFORIA. In particular, we consider
a mono-energetic 4 MeV proton injection over an extended region located at a
heliographic radial distance of 0.1 AU. By using different values for the
perpendicular proton mean free path, we study how cross-field diffusion may
affect the energetic particle spread and intensity profiles near a high-speed
solar wind stream and a corotating interaction region (CIR). We find that both
a strong cross-field diffusion and a solar wind rarefaction region are capable
of dispersing SEPs efficiently, producing overall low particle intensities
which can in some cases prevent the SEPs from being detected in-situ, since
their intensity may drop below the detected pre-event intensity levels. We also
discuss how accelerated particle populations form on the reverse and forward
shock waves, separated by the stream interface inside the CIR. Under strong
levels of cross-field diffusion, particles cross the SI and hence both
accelerated particle populations merge together.

Space Physics