The composition, propagation and acceleration of energetic solar particles: A review of United States research 1979–1982

Abstract

We study solar energetic particles in an effort to better understand physical processes which occur at the Sun and in the heliosphere, but improvements in our understanding of the physics of these processes should have broader implications in more general astrophysical problems. Among the questions of greatest interest are: (l) what is the basic elemental and isotopic composition of the solar atmosphere, to what extent is this composition reflected in observed energetic solar particles and how do these abundances relate to or influence our understanding of universal and galactic cosmic ray abundances; (2) by what mechanisms, under what conditions and where does the acceleration of solar energetic particles take place; (3) what are the mechanisms by which energetic particles are transported and/or stored in the vicinity of the Sun; (4) how can we describe the escape from the Sun and subsequent transport of charged solar particles through interplanetary space and how can we relate that description to measurable properties of the medium through which they travel?Each of the above points raises numerous and difficult subsidiary questions. But probably the primary obstacle to direct study of these problems is that the various processes and mechanisms are almost inextricably interwoven observationally (Wibberenz, 1979). All measurements that we make of particles in space (e.g., composition, time evolution of intensities and anisotropies, energy spectra) are influenced both by the nature of the original particle acceleration and by the propagation of these particles from the acceleration site to the observing instruments.