The Abundance of Helium in the Source Plasma of Solar Energetic Particles

Abstract

Studies of patterns of abundance enhancements of elements, relative to solar-coronal abundances, in large solar energetic-particle (SEP) events, and of their power-law dependence on the mass-to-charge ratio A/Q of the ions, have been used to determine the effective source-plasma temperature T that defines the Q-values of the ions. We find that a single assumed value for the coronal reference He/O ratio in all SEP events is often inconsistent with the transport-induced power-law trend of the other elements. In fact, the coronal He/O actually varies rather widely from one SEP event to another. In the large Fe-rich SEP events with T = 3 MK, where shock waves, driven out by coronal mass ejections (CMEs), have reaccelerated residual ions from impulsive suprathermal events that occur earlier in solar active regions, He/O = 90, a ratio similar to that in the slow solar wind, which may also originate from active regions. Ions in the large SEP events with T < 2 MK may be accelerated outside active regions, and have values of 40 < He/O < 60. Mechanisms that determine coronal abundances, including variations of He/O, are likely to occur near the base of the corona (at ~ 1.1 RS) and thus to affect both SEPs (at ~2 - 3 RS) and the solar wind. Other than He, reference coronal abundances for heavier elements show little temperature dependence or systematic difference between SEP events; He, the element with the highest first ionization potential, is unique. The CME-driven shock waves probe the same regions of space, at ~2 RS near active regions, which are also likely sources of the slow solar wind, providing complementary information on conditions in those regions.

28 pages, 13 figures, accepted by Solar Physics

References in corpus (7)

• 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
• Plasma parameters and geometry of cool and warm active region loops
• Charge States and FIP Bias of the Solar Wind from Coronal Holes, Active Regions, and Quiet Sun
• Spatial Distribution of Element Abundances and Ionization States in Solar Energetic-Particle Events
• Element Abundances and Source Plasma Temperatures of Solar Energetic Particles

Cited by in corpus (16)

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• Four Distinct Pathways to the Element Abundances in Solar Energetic Particles
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• Sixty Years of Element Abundance Measurements in Solar Energetic Particles
• 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
• Heating of Heavy Ions in Low-beta Compressible Turbulence
• Solar Energetic Particles: Spatial Extent and Implications of the H and He Abundances
• Excess H, Suppressed He, and the Abundances of Elements in Solar Energetic Particles
• Energy Spectra vs. Element Abundances in Solar Energetic Particles and the Roles of Magnetic Reconnection and Shock Acceleration
• Solar Energetic Particle Charge States and Abundances with Nonthermal Electrons
• Element Abundances of Solar Energetic Particles and the Photosphere, the Corona, and the Solar Wind
• Seeds and Sequences of Element Abundances in Solar Energetic Particle Events
• Heavy Ion Acceleration by Super-Alfvenic Waves
• A Perspective on Solar Energetic Particles