  Abundances of elements comprising solar energetic particles (SEPs) come with
two very different patterns. Historically called "impulsive" and "gradual"
events, they have been studied for 40 years, 20 years by the Wind spacecraft.
Gradual SEP events measure coronal abundances. They are produced when shock
waves, driven by coronal mass ejections (CMEs), accelerate the ambient coronal
plasma; we discuss the average abundances of 21 elements that differ from
corresponding solar photospheric abundances by a well-known dependence on the
first ionization potential (FIP) of the element. The smaller impulsive
("3He-rich") SEP events are associated with magnetic reconnection involving
open field lines from solar flares or jets that also eject plasma to produce
accompanying CMEs. These events produce striking heavy-element abundance
enhancements, relative to coronal abundances, by an average factor of 3 at Ne,
9 at Fe, and 900 for elements with 76<Z<82. This is a strong, power-law
dependence on A/Q with a ~3.6 power when Q values are determined at coronal
temperatures near 3 MK. Small individual SEP events with the steepest
enhancements (~6th power of A/Q), from ~2.5 MK plasma, are associated with B-
and C-class X-ray flares, and with narrow (<100 deg) CMEs. Enhancements in
3He/4He can be as large as those in heavy elements but are uncorrelated with
them. However, events with 3He/4He > 0.1 are even more strongly associated with
narrow, slow CMEs, cooler coronal plasma, and smaller X-ray flares. The
impulsive SEP events do not come from hot flare plasma; they are accelerated
early and/or on adjacent open field lines.
