Global Numerical Modeling of Energetic Proton Acceleration in a Coronal Mass Ejection Traveling Through the Solar Corona

Abstract

The acceleration of protons and electrons to high (sometimes GeV/nucleon) energies by solar phenomena is a key component of space weather. These solar energetic particle (SEP) events can damage spacecraft and communications, as well as present radiation hazards to humans. In-depth particle acceleration simulations have been performed for idealized magnetic fields for diffusive acceleration and particle propagation, and at the same time the quality of MHD simulations of coronal mass ejections (CMEs) has improved significantly. However, to date these two pieces of the same puzzle have remained largely decoupled. Such structures may contain not just a shock but also sizable sheath and pileup compression regions behind it, and may vary considerably with longitude and latitude based on the underlying coronal conditions. In this work, we have coupled results from a detailed global three-dimensional MHD time-dependent CME simulation to a global proton acceleration and transport model, in order to study time-dependent effects of SEP acceleration between 1.8 and 8 solar radii in the 2005 May 13 CME. We find that the source population is accelerated to at least 100 MeV, with distributions enhanced up to six orders of magnitude. Acceleration efficiency varies strongly along field lines probing different regions of the dynamically evolving CME, whose dynamics is influenced by the large-scale coronal magnetic field structure. We observe strong acceleration in sheath regions immediately behind the shock.

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

“…This is essential to find the correct solution of DSA. The shock thickness resolved in this study is much less than the cell size of MHD simulations that include the calculation of particle acceleration in a similar way (e.g., Kozarev et al 2013;Schwadron et al 2015).…”

“…In particular, as mentioned earlier, compelling observational evidence exists for the shock formation and particle acceleration close to the Sun. Therefore, modeling shock acceleration in the low corona is of great importance for understanding the underlying mechanisms for producing large SEP events (e.g., Berezhko & Taneev 2003Kocharov et al 2005;Vainio & Laitinen 2007;Ng & Reames 2008;Sandroos & Vainio 2009a, 2009bKozarev et al 2013;Schwadron et al 2015). Ng & Reames (2008) modeled particle acceleration at a parallel shock with a speed of 2500 km s −1 starting at 3.5 R e and showed that particles can be accelerated to >300 MeV in 10 minutes.…”

The Coronal Analysis of SHocks and Waves (CASHeW) framework

“…Beyond its use for characterization of CBFs, it can be important for the SEP acceleration process. As shown in multiple studies (Manchester et al, 2005;Giacalone & Kóta, 2006;Kozarev et al, 2013;Schwadron et al, 2015), SEPs may be accelerated also in the pile-up region behind shocks or in compressive waves that do not exhibit the step-like plasma change characteristic of shocks provided the particles possess enough energy.…”

“…Detailed simulations of particle acceleration in realistically modeled CMEs near the Sun show that shocks form very early and can accelerate protons to hundreds of MeV (Sokolov et al, 2009;Kozarev et al, 2013). However, due to the lack of in situ measurements of particles and fields in the corona, our understanding of the acceleration and transport processes there is quite limited.…”

Modelling large solar proton events with the shock-and-particle model

“…Other factors, like different seed particle populations (e.g., Li & Zank 2005;Tylka et al 2005;Battarbee et al 2011;Vainio et al 2014) or the inclusion of a variable magnetic field (i.e. non-Parker morphology of the IMF) as studied by different authors (e.g., Giacalone 2005;Kocharov et al 2009;Guo et al 2010;Kozarev et al 2013), have not been included in SaP yet. Our next step, together with the improvement of the modelling of the foreshock region as commented on in the previous section, is to study the correlation between Q and other parameters, particularly with h Bn , in order to, eventually, find a multi-parameter dependence of Q.…”