Abstract
Abstract We propose a model for interpreting highly variable ion composition ratios in solar energetic particle (SEP) events recently observed by the Parker Solar Probe (PSP) at 0.3–0.45 au. We use numerical simulations to calculate SEP propagation in a turbulent interplanetary magnetic field with a Kolmogorov power spectrum from large scales 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 3He/4He source ratio of 10% in impulsive 3He-rich events and the same spatial offset of the source regions, the 3He/4He 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 implications of these results on the variability of ion composition of impulsive events and on further PSP and Solar Orbiter observations close to the Sun.
Highlights
The acceleration and transport of energetic charged particles is a remarkable problem in heliophysics and astrophysics
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 have shown in this paper that this variation can possibly be due to the propagation of SEPs in braiding interplanetary magnetic field lines of force, if the source regions are offset
Summary
The acceleration and transport of energetic charged particles is a remarkable problem in heliophysics and astrophysics. The model solves the propagation of SEPs instantaneously released at compact sources in synthetic solar wind magnetic turbulence (Matthaeus et al 1990; Giacalone & Jokipii 1999; Guo & Giacalone 2014). We use the composite model, which is a magnetostatic model for the wave-vector spectrum of magnetic fluctuations based on observations of the solar wind turbulence (Matthaeus et al 1990). In the model we consider, the wave propagation is not included and the time dependence is only through the solar wind advection as the magnetic field is frozen in the background plasma. It would be interesting to consider more realistic geometry and spatial dependence of background solar-wind plasma parameters, magnetic field and their fluctuations, as they may vary considerably in latitudinal and lonitudinal directions (e.g., Giacalone et al 2000; Zhao et al 2020)
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