This concise primer introduces the non-specialist reader to the physics of solar energetic particles (SEP) and systematically reviews the evidence for the two main mechanisms which lead to the so-called impulsive and gradual SEP events.
More specifically, the timing of the onsets, the longitude distributions, the high-energy spectral shapes, the correlations with other solar phenomena (e.g. coronal mass ejections), as well as the all-important elemental and isotopic abundances of SEPs are investigated. Impulsive SEP events are related to magnetic reconnection in solar flares and jets. The concept of shock acceleration by scattering on self-amplified Alfven waves is introduced, as is the evidence of reacceleration of impulsive-SEP material in the seed population accessed by the shocks in gradual events. The text then develops processes of transport of ions out to an observer. Finally, a new technique to determine the source plasma temperature in both impulsive and gradual events is demonstrated.
Last but not least the role of SEP events as a radiation hazard in space is mentioned and a short discussion of the nature of the main particle telescope designs that have contributed to most of the SEP measurements is given.
Don Reames received his A.B. and Ph.D. degrees in physics from the University of California at Berkeley in 1958 and 1964, respectively. He applied this early background in nuclear physics to his work in experimental astrophysics at Goddard Space Flight Center since 1964. His early work involved the S9 Cosmic Ray Experiment flown on the Gemini XI mission and sounding rockets flown from Ft. Churchill. He subsequently worked with experiments on the ISEE-3, IMP-8, Helios 1 and 2, and Wind spacecraft. As a Co-I on the EPACT experiment on the Wind spacecraft, he was responsible for the design and construction of the Low Energy Matrix Telescope (LEMT). He is also a Co-I on IMPACT experiment for the STEREO mission. He has studied the physics of particle acceleration in a variety of sites throughout the heliosphere and the relationship of these particles to solar flares, shock waves, CMEs and to the radio, X-ray, and gamma-ray emission that they particles produce. This work has resulted in over 100 papers in the refereed scientific literature. Don Reames retired from the Civil Service in 2003 to continue in an Emeritus position at Goddard. In 2007 he joined the Institute for Physical Science and Technology at the University of Maryland, College Park, MD where he is a Senior Research Scientist.
Introduction.- History.- Distinguishing Two Sources.- Impulsive SEP events.- Gradual SEP Events.- High Energies and Radiation Effects.- Measurements of SEPs.- Summary and Conclusions.