Solar energetic particles: Sampling coronal abundances

In the large solar energetic particle (SEP) events, coronal mass ejections (CMEs) drive shock waves out through the corona that accelerate elements of the ambient material to MeV energies in a fairly democratic, temperature-i ndependent manner. These events provide the most complete source of informa tion on element abundances in the corona. Relative abundances of 22 element s from H through Zn display the well-known dependence on the first ionizati on potential (FIP) that distinguishes coronal and photospheric material. Fo r most elements, the main abundance variations depend upon the gyrofrequenc y, and hence on the charge-to-mass ratio, Q/A, of the ion. Abundance variat ions in the dominant species, H and He, are not Q/A dependent, presumably b ecause of nonlinear wave-particle interactions of H and He during accelerat ion. Impulsive flares provide a different sample of material that confirms the Ne:Mg:Si and He/C abundances in the corona.