The most complete measurements of elemental abundances in the solar
corona come from measurements of high energy particles accelerated in the large Solar
Energetic Particle (SEP)
Initially it was thought that the energetic particles in large
SEP events were accelerated in solar flares.
In recent years, however, it has become clear that in the large gradual
events particles are accelerated at shock waves that are driven
out from the Sun by Coronal Mass Ejections (CMEs).
These shocks accelerate the ions of the chemical elements in a fairly equivalent manner.
In contrast, particles accelerated in impulsive solar
flares show specific elemental enhancements produced by resonant
wave-particle interactions during stochastic acceleration of the
ions from the flare plasma.
New spacecraft observations can extend Solar Energetic Particle
measurements to heavier elements, to rarer elements and to
NINA can perform SEP observations in the polar sectors
of the orbit for a relatively long period of the 23rd solar cycle.
Its good mass discrimination can help in the
determination of their composition and therefore in the
comprehension of the sources and acceleration mechanisms involved.