Solar Energetic Particle Acceleration at Shock Waves Driven by Fast and Wide Coronal Mass Ejections

We present the results from numerical simulations of solar energetic particles (SEPs) accelerated by shock waves driven by fast and wide coronal mass ejections (CMEs) with shock parameters - such as the Mach number, speed, and shock-normal angle - varying with time and space. The variation in these parameters are determined by combining magnetohydrodynamic (MHD) simulations of the solar corona with coronagraphic observations of CMEs from STEREO-A, STEREO-B, and SOHO on 2011 March 07 and 2011 October 01. We model the acceleration and transport of particles in these events by numerically solving the Parker transport equation for a spherically symmetric shock. The shock is moving outward from the Sun with the shock parameters that vary with time along the intersection point between the shock surface and the magnetic field line that connects to each spacecraft. We find that the acceleration efficiency is significantly affected by the local Mach number and diffusion coefficient κ. For example, when the Mach number is large and the shock is very close to the Sun (small κ), the acceleration is highly efficient with the fluxes of high-energy protons enhanced rapidly. Also, other parameters such as the solar wind speed, the intensity of the seed particle population and the shock normal angles can alter the resulting SEP intensities as well. These results suggest that SEP fluxes can change dramatically over a wide range of heliolongitudes, and the magnetic connections of spacecraft to these `highly efficient regions' are potentially important for the observation of SEP events related to fast and wide CMEs.