  Particles measured in large gradual solar energetic particle (SEP) events are
believed to be predominantly accelerated at shocks driven by coronal mass
ejections (CMEs). Ion charge state and composition analyses suggest that the
origin of the seed particle population for the mechanisms of particle
acceleration at CME-driven shocks is not the bulk solar wind thermal material,
but rather a suprathermal population present in the solar wind. This
suprathermal population could result from remnant material accelerated in prior
solar flares and/or preceding CME-driven shocks. In this work, we examine the
distribution of this suprathermal particle population in the inner heliosphere
by combining a magnetohydrodynamic (MHD) simulation of the solar wind and a
Monte-Carlo simulation of particle acceleration and transport. Assuming that
the seed particles are uniformly distributed near the Sun by solar flares of
various magnitudes, we study the longitudinal distribution of the seed
population at multiple heliocentric distances. We consider a non-uniform
background solar wind, consisting of fast and slow streams that lead to
compression and rarefaction regions within the solar wind. Our simulations show
that the seed population at a particular location (e.g., 1 au) is strongly
modulated by the underlying solar wind configuration. Corotating interaction
regions (CIRs) and merged interactions regions (MIRs) can strongly alter the
energy spectra of the seed particle populations. In addition, cross-field
diffusion plays an important role in mitigating strong variations of the seed
population in both space and energy.
