The first models for SEP events assumed that particle
injection occurred in spatial and temporal conjunction
with the associated solar flare. However, since (1) flare
activity lasts just, at most, for a few hours and low-energy
ion events last for several days, and (2) SEP events
were associated with events occurring from anywhere in
the solar disk (even sometimes beyond the limbs of the
Sun), it was suggested that energetic particles may remain
stored in the solar corona and diffuse across the
coronal field to reach widespread ranges of heliolongitudes.
Such models (Smart and Shea, 1992; Heckman
et al., 1992) failed to include the effects of shocks and
their prediction for particle intensities were based on
the characteristics of the associated solar flare (such as
location, X-ray and radio bursts intensities). Apart from
their inability to reproduce ESP events, particle transport
through the interplanetary medium was based
on simple static diffusion models (see details in the
references above)