Variable Ion Compositions of Solar Energetic Particle Events in the Inner Heliosphere: A Field-line Braiding Model with Compound Injections

Abstract

We propose a model for interpreting highly variable ion composition ratios in solar energetic particles (SEP) events recently observed by Parker Solar Probe (PSP) at $0.3-0.45$ astronomical unit. We use numerical simulations to calculate SEP propagation in a turbulent interplanetary magnetic field with a Kolmogorov power spectrum from large scale down to the gyration scale of energetic particles. We show that when the source regions of different species are offset by a distance comparable to the size of the source regions, the observed energetic particle composition He/H can be strongly variable over more than two orders of magnitude, even if the source ratio is at the nominal value. Assuming a ${}^3$He/${}^4$He source ratio of $10\%$ in impulsive ${}^3$He-rich events and the same spatial offset of the source regions, the ${}^3$He/${}^4$He ratio at observation sites also vary considerably. The variability of the ion composition ratios depends on the radial distance, which can be tested by observations made at different radial locations. We discuss the implication of these results on the variability of ion composition of impulsive events and on further PSP and Solar Orbiter observations close to the Sun.

10 pages, 5 figures, ApJ accepted

References in corpus (12)

• Formation of Hard Power-laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection
• Electron Acceleration during Macroscale Magnetic Reconnection
• Imaging and spectroscopic observations of magnetic reconnection and chromospheric evaporation in a solar flare
• The Acceleration of Electrons at Collisionless Shocks Moving Through a Turbulent Magnetic Field
• The FIP and Inverse FIP Effects in Solar Flares
• Observations of the 2019 April 4 Solar Energetic Particle Event at the Parker Solar Probe
• The Onset of Ion Heating During Magnetic Reconnection with a Strong Guide Field
• Magnetic Field Line Random Walk and Solar Energetic Particle Path Lengths: Stochastic Theory and PSP/ISoIS Observation
• Particle acceleration in kinetic simulations of non-relativistic magnetic reconnection with different ion-electron mass ratio
• Temperature in Solar Sources of 3He-rich Solar Energetic Particles and Relation to Ion Abundances
• Heating of Heavy Ions in Low-beta Compressible Turbulence
• Efficient Nonthermal Ion and Electron Acceleration Enabled by the Flux-Rope Kink Instability in 3D Nonrelativistic Magnetic Reconnection