Energetic particle acceleration and transport at coronal mass ejection–driven shocks

Abstract

[1] Evidence now exists which suggests that in large solar energetic particle (SEP) events, particles are often accelerated to $ MeV energies (and perhaps up to GeV energies) at shock waves driven by coronal mass ejections (CMEs). These energetic particles are of considerable importance to space weather studies since they serve as a precursor signal for possible disruptive events at the Earth. As a CME-driven shock propagates, expands and weakens, particles accelerated diffusively at the shock can escape upstream and downstream into the interplanetary medium. The escaping energized particles propagate along the interplanetary magnetic field, experiencing only weak scattering from fluctuations in the interplanetary magnetic field (IMF). In this work, we study the timedependent transport of energetic particles accelerated at a propagating shock using a Monte-Carlo approach. This treatment, together with our previous work on particle acceleration at shocks, allows us to investigate the characteristics (intensity profiles, angular distribution, particle anisotropies) of high-energy particles arriving at various distances from the sun. Such an approach is both easy to implement and allows us to study the affect of interplanetary turbulence on particle transport in a systematic manner. These theoretical models form an excellent basis on which to interpret observations of highenergy particles made in situ at 1 AU by spacecraft such as ACE and WIND.

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

“…A relevant model pertaining to the latter category that has been applied to analyse actual SEP events from a space weather viewpoint is the PATH (Particle Acceleration and Transport in the Heliosphere) code (Verkhoglyadova et al 2009(Verkhoglyadova et al , 2010(Verkhoglyadova et al , 2012. Being a realization of the model by Zank et al (2000), Rice et al (2003) and Li et al (2003), this code uses the theory of diffusive shock acceleration to model particle acceleration at shocks. It assumes an analytic approximation of the spectrum of the accelerated particles derived from the properties of the shock obtained through an MHD model.…”

Energetic particle parallel diffusion in a cascading wave turbulence in the foreshock region

“…Hence, the spatial dependence of λ (x) cannot be described only by the spatial evolution of δB 2 . Based on our results, one can estimate the parameter β, which models the spatial dependence of λ in the empirical approach by Li et al (2003).…”

“…In numerical models for particle accelerations at a quasi-parallel interplanetary shock (Zank et al, 2000;Li et al, 2003Li et al, , 2005, the spatial dependence is empirically introduced by index β as a free parameter, λ ∼ p α r β , where r is radial distance from the sun, p is particle momentum, and α is an index of the momentum dependence. We find that the model based on the QLT is not sufficient for description of the relationship between spatial variations of the mean free path and the statistics of MHD waves.…”

Heavy ion acceleration at parallel shocks

“…In spite of successful explanation by DSA-based analytical and numerical models (Lee, 1983;Jokipi, 1987;Gordon et al, 1999;Zank et al, 2000;Li et al, 2003Li et al, , 2005Giacolone and Kota, 2006) of many important features of the acceleration process, for example power spectra of accelerated particles, dependence of accelerated particles on the distance from the shock front and many others, there are important questions that remain open for a long time.…”