  Forecasting large Solar Energetic Particle (SEP) events associated with
shocks driven by fast coronal mass ejections (CME) pose a major difficulty in
the field of Space Weather. Besides issues associated with CME initiation, the
SEP intensities are difficult to predict, spanning 3 orders of magnitude at any
given CME speed. Many lines of indirect evidence point to the pre-existence of
suprathermal seed particles for injection into the acceleration process as a
key ingredient limiting the SEP intensity of a given event. This paper outlines
the observational and theoretical basis for the inference that a suprathermal
particle population is present prior to large SEP events, explores various
scenarios for generating seed particles and their observational signatures, and
explains how such suprathermals could be detected through measuring the wings
of the H I Ly-alpha line.
