  Thirty years ago Breneman and Stone observed that the enhancement or
suppression of element abundances in large solar energetic-particle (SEP)
events varies as a power of the mass-to-charge ratio, A/Q, of the elements.
Since Q during acceleration or transport may depend upon the source plasma
temperature T, the pattern of element enhancements can provide a best-fit
measure of T. The small SEP events we call 3He-rich or "impulsive" show average
enhancements, relative to coronal abundances, rising as the 3.6 power of A/Q to
a factor of ~1000 for (76<=Z<=82)/O and temperature in the range 2-4 MK. This
acceleration is believed to occur in islands of magnetic reconnection on open
field lines in solar flares and jets. It has been recently found that the large
shock-accelerated "gradual" SEP events have a broad range of source plasma
temperatures; 69% have coronal temperatures of T < 1.6 MK, while 24% have T ~ 3
MK, the latter suggesting a seed population containing residual impulsive
suprathermal ions. Most of the large event-to-event abundance variations and
their time variation are largely explained by variations in T magnified by
A/Q-dependent fractionation during transport. However, the non-thermal variance
of impulsive SEP events (~30%) exceeds that of the ~3 MK gradual events (~10%)
so that several small impulsive events must be averaged together with the
ambient plasma to form the seed population for shock acceleration in these
events.
