Fifty Years of 3He-rich Events

Abstract

The early 1970s saw a new and surprising feature in the composition of solar energetic particles (SEPs), resonant enhancements up to 10,000-fold in the ratio 3He/4He that could even make 3He dominant over H in rare events. It was soon learned that these events also had enhancements in the abundances of heavier elements, such as a factor of ~10 enhancements in Fe/O, which was later seen to be part of a smooth increase in enhancements vs. mass-to-charge ratio A/Q from H to Pb, rising by a factor of ~1000. These events were also associated with streaming 10 - 100 keV electrons that produce type III radio bursts. In recent years we have found these "impulsive" SEP events to be accelerated in islands of magnetic reconnection from plasma temperatures of 2 - 3 MK on open field lines in solar jets. Similar reconnection on closed loops traps the energy of the particles to produce hot (>10 MK), bright flares. Sometimes impulsive SEP intensities are boosted by shock waves when the jets launch fast coronal mass ejections. No single theory yet explains both the sharp resonance in 3He and the smooth increase up to heavier elements; two processes seem to occur. Sometimes the efficient acceleration even exhausts the rare 3He in the source region, limiting its fluence.

13 pages, 5 figures, published open access by Frontier

References in corpus (13)

• Electron Acceleration during Macroscale Magnetic Reconnection
• Abundance Enhancements in Impulsive Solar Energetic-Particle Events with Associated Coronal Mass Ejections
• 3He-rich solar energetic particles: Solar sources
• Multi-Spacecraft Observations of Recurrent 3He-Rich Solar Energetic Particles
• Four Distinct Pathways to the Element Abundances in Solar Energetic Particles
• 3He-Rich Solar Energetic Particles in Helical Jets on the Sun
• Variations in Abundance Enhancements in Impulsive Solar Energetic-Particle Events and Related CMEs and Flares
• 3He-Rich Solar Energetic Particles from Sunspot Jets
• Sixty Years of Element Abundance Measurements in Solar Energetic Particles
• Relative Spectra and Distributions of Fluences of 3He and 4He in Solar Energetic Particles
• Hydrogen and the Abundances of Elements in Impulsive Solar Energetic-Particle Events
• Association of 3He-Rich Solar Energetic Particles with Large-Scale Coronal Waves
• Temperature in Solar Sources of 3He-rich Solar Energetic Particles and Relation to Ion Abundances

Cited by in corpus (5)

• Energy Spectra vs. Element Abundances in Solar Energetic Particles and the Roles of Magnetic Reconnection and Shock Acceleration
• Seeds and Sequences of Element Abundances in Solar Energetic Particle Events
• Origin of Unusual Composition of 3He-Rich Solar Energetic Particles
• A Perspective on Solar Energetic Particles
• Spectra of He isotopes and the ${}^3$He/${}^4$He ratio