Element Abundances and Source Plasma Temperatures of Solar Energetic Particles
arXiv:1612.00030 · doi:10.1088/1742-6596/767/1/012023
Abstract
Thirty years ago Breneman and Stone observed that the enhancement or suppression of element abundances in large solar energetic-particle (SEP) events varies as a power of the mass-to-charge ratio, A/Q, of the elements. Since Q during acceleration or transport may depend upon the source plasma temperature T, the pattern of element enhancements can provide a best-fit measure of T. The small SEP events we call 3He-rich or "impulsive" show average enhancements, relative to coronal abundances, rising as the 3.6 power of A/Q to a factor of ~1000 for (76<=Z<=82)/O and temperature in the range 2-4 MK. This acceleration is believed to occur in islands of magnetic reconnection on open field lines in solar flares and jets. It has been recently found that the large shock-accelerated "gradual" SEP events have a broad range of source plasma temperatures; 69% have coronal temperatures of T < 1.6 MK, while 24% have T ~ 3 MK, the latter suggesting a seed population containing residual impulsive suprathermal ions. Most of the large event-to-event abundance variations and their time variation are largely explained by variations in T magnified by A/Q-dependent fractionation during transport. However, the non-thermal variance of impulsive SEP events (~30%) exceeds that of the ~3 MK gradual events (~10%) so that several small impulsive events must be averaged together with the ambient plasma to form the seed population for shock acceleration in these events.
arXiv comment8pages,7 figures, 15th Ann. Intl. Astrophys. Conf. "The Science of Ed Stone: Celebrating his 80th Birthday"
References in corpus (10)
- The chemical composition of the Sun
- Ionization balance for optically thin plasmas: rate coefficients for all atoms and ions of the elements H to Ni
- The Two Sources of Solar Energetic Particles
- Element Abundances in Solar Energetic Particles and the Solar Corona
- What are the Sources of Solar Energetic Particles? Element Abundances and Source Plasma Temperatures
- Abundance Enhancements in Impulsive Solar Energetic-Particle Events with Associated Coronal Mass Ejections
- Multi-Spacecraft Observations of Recurrent 3He-Rich Solar Energetic Particles
- Variations in Abundance Enhancements in Impulsive Solar Energetic-Particle Events and Related CMEs and Flares
- Temperature of the Source Plasma in Gradual Solar Energetic Particle Events
- The State of Self-Organized Criticality of the Sun During the Last 3 Solar Cycles. I. Observations