Composition of Energetic Solar Particles

Abstract

Present state of our knowledge on the composition of energetic solar particles is reviewed with particular reference to the direct measurements of these particles with sounding rockets and balloons during solar cosmic ray events. The observational data on the energy spectra and relative abundances of hydrogen, helium and heavy nuclei measured at different times during a number of solar events are discussed in order to delineate the characteristics features of solar cosmic rays. The implications of these results are discussed in relation to the propagation of solar cosmic rays, the relative abundances of elements in the sun and the composition of galactic cosmic rays. It is shown that the relative abundances of multiply charged nuclei measured in solar cosmic rays represent an unbiased sample of these nuclei from the sun and hence the photospheric abundances of helium, carbon, nitrogen, oxygen, neon and iron group are now obtain from solar cosmic rays. By combining the ratio of helium to oxygen measured in solar cosmic rays with that of hydrogen to oxygen obtained by spectroscopic means, the hydrogen to helium ratio in the sun is determined as 16±2. A comparison of the composition of energetic solar particles with that of galactic cosmic rays reveals some striking differences; this indicates that ordinary stars like the sun cannot be the main source of cosmic rays.