SpreadFast Project

The heliospheric transport of solar energetic particles in the heliosphere will be treated with the global, three-dimensional EPREM code. EPREM is a versatile, parallelized numerical kinetic model for the global propagation and acceleration of energetic charged particles of solar origin in the heliosphere. It has been extensively validated on different problems of heliospheric charged particle acceleration and transport (Schwadron et al. 2010). It has also been successfully coupled to various global MHD solar wind models,

such as Enlil (Kozarev et al. 2010)¹, SWMF (Kozarev et al. 2013), and CORHEL (Schwadron et al. 2015)². The model solves a modified version of the field aligned transport equation (Kota et al. 2005)³ for the acceleration and transport of protons distributed in pitch angle and momentum. It accounts for particle streaming, adiabatic focusing, adiabatic heating and cooling, convection, pitch-angle scattering, and stochastic acceleration. It uses a dynamic Lagrangian grid (shown in Fig. 1E for a Parker spiral-type solar wind), which allows for efficient computation of changes in the particle distribution function. The model takes particle distribution function spectra as inner boundary conditions. EPREM calculates the diffusion coefficients based on the large-scale and fluctuating magnetic field components. Wave growth is controlled by a wave kinetic equation that is solved time-dependently on the entire simulation grid. We will develop an interface to EPREM as part of the work on Work Package 2. Fig. 1, panels G and H show time-dependent fluxes on two separate field lines generated with EPREM in a simulation with time-independent realistic (derived from 1 AU observations) input spectra and an evolving CME, from Kozarev et al. (2013).