The Origin of Element Abundance Variations in Solar Energetic Particles

Abstract

Abundance enhancements, during acceleration and transport in both gradual and impulsive solar energetic particle (SEP) events, vary approximately as power laws in the mass-to-charge ratio [A/Q] of the ions. Since the Q-values depend upon the electron temperature of the source plasma, this has allowed a determination of this temperature from the pattern of element-abundance enhancements and a verification of the expected inverse-time dependence of the power of A/Q for diffusive transport of ions from the SEP events, with scattering mean free paths found to be between 0.2 and 1 AU. SEP events derived from plasma of different temperatures map into different regions in typical cross-plots of abundances, spreading the distributions. In comparisons of SEP events with temperatures above 2 MK, impulsive events show much broader non-thermal variation of abundances than do gradual events. The extensive shock waves accelerating ions in gradual events may average over much of an active region where numerous but smaller magnetic reconnections, "nanojets", produce suprathermal seed ions, thus averaging over varying abundances, while an impulsive SEP event only samples one local region of abundance variations. Evidence for a reference He/O abundance ratio of 91, rather than 57, is also found for the hotter plasma. However, while this is similar to the solar-wind abundance of He/O, the solar-wind abundances otherwise provide an unacceptably poor reference for the SEP abundance enhancements, generating extremely large errors.

24 pages, 10 figures

References in corpus (11)

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• The "FIP Effect" and the Origins of Solar Energetic Particles and of the Solar Wind
• Sixty Years of Element Abundance Measurements in Solar Energetic Particles
• The Abundance of Helium in the Source Plasma of Solar Energetic Particles
• Why is solar cycle 24 an inefficient producer of high-energy particle events?
• Hydrogen and the Abundances of Elements in Impulsive Solar Energetic-Particle Events
• Hydrogen and the Abundances of Elements in Gradual Solar Energetic-Particle Events
• Helium Suppression in Impulsive Solar Energetic-Particle Events
• Corotating Shock Waves and the Solar-Wind Source of Energetic Ion Abundances: Power Laws in A/Q
• Spatial Distribution of Element Abundances and Ionization States in Solar Energetic-Particle Events
• Excess H, Suppressed He, and the Abundances of Elements in Solar Energetic Particles
• Element Abundances of Solar Energetic Particles and the Photosphere, the Corona, and the Solar Wind
• A Perspective on Solar Energetic Particles