The Acceleration of High-energy Protons at Coronal Shocks: The Effect of Large-scale Streamer-like Magnetic Field Structures

Abstract

Recent observations have shown that coronal shocks driven by coronal mass ejections can develop and accelerate particles within several solar radii in large solar energetic particle (SEP) events. Motivated by this, we present an SEP acceleration study that including the process in which a fast shock propagates through a streamer-like magnetic field with both closed and open field lines in the low corona region. The acceleration of protons is modeled by numerically solving the Parker transport equation with spatial diffusion both along and across the magnetic field. We show that particles can be sufficiently accelerated to up to several hundred MeV within 2-3 solar radii. When the shock propagates through a streamer-like magnetic field, particles are more efficiently accelerated compared to the case with a simple radial magnetic field, mainly due to perpendicular shock geometry and the natural trapping effect of closed magnetic fields. Our results suggest that the coronal magnetic field configuration is an important factor for producing large SEP events. We further show that the coronal magnetic field configuration strongly influences the distribution of energetic particles, leading to different locations of source regions along the shock front where most high-energy particles are concentrated. This work may have strong implications for SEP observations. The upcoming Parker Solar Probe will provide in situ observations for the distribution of energetic particles in the coronal shock region, and test the results of the study.

Multiple Sources of Solar High-energy Protons

“…Such shocks can efficiently accelerate both the interacting protons producing the pion decay γ-ray emissions at the Sun and the interplanetary protons responsible for the prompt component of the GLE at the Earth. Several relevant acceleration models were considered by Kocharov et al (2011Kocharov et al ( , 2012, Kong et al (2017), and Kouloumvakos et al (2020).…”

Connecting the Properties of Coronal Shock Waves with Those of Solar Energetic Particles

“…The resulting correlations are not statistically significant, and an apparent relation is difficult to establish from Figure 9. Recent studies have shown that for a realistic coronal structure the seed particles gain energy gradually by interacting with a rapidly varying shock geometry (e.g., Sandroos & Vainio 2009;Kong et al 2017). A proper evaluation of the role of shock geometry on the acceleration process requires a more refined analysis that folds in time dependency.…”

Shock Propagation and Associated Particle Acceleration in the Presence of Ambient Solar-Wind Turbulence

“…They demonstrated that the familiar planar-shock results can be significantly altered as a consequence of large-scale, meandering magnetic lines of force. Because the perpendicular diffusion coefficient κ ⊥ is generally much smaller than the parallel diffusion coefficient κ , energetic charged particles are trapped and preferentially accelerated along the shock front in regions where the connection points of magnetic field lines intersecting the shock surface converge, and thus create "hot spots" of accelerated particles (see also Kong et al, 2017;Kong et al, 2019a). For regions where the connection points are separated from each other, the acceleration to high energies will be suppressed.…”