EPREM

The Energetic Particle Radiation Environment Module (EPREM) models acceleration and transport of ions throughout the heliosphere by numerically solving the focused transport equation on a Lagrangian grid in the frame co-moving with the solar wind plasma. EPREM manages a set of nested surfaces on which it places simulation nodes that move under the influence of external MHD forces. Each node contains local information about the evolution of the ion distribution function and other relevant physical quantities. Connected nodes form the simulation streams at the core of the output data files.

At the CCMC, EPREM can be run in different ways:

1. EPREM: assuming a Parker Spiral IMF, background conditions.
2. EPREM+Cone: assuming a Parker Spiral IMF, with an inserted idealized "cone" shock into the EPREM domain.
3. Future Capability -- EPREM+ENLIL: uses a WSA-ENLIL+Cone run as it's domain. For this option, first an WSA-ENLIL+Cone simulation with appropriate settings must be selected from the run database.

EPREM requires values of the magnetic field, velocity field, and density in the ambient plasma in order to update the ion distribution function via the focused transport equation. By default, it will compute values for those three plasma quantities according to a standard Parker Spiral, an idealized shock representing a cone CME can also be included. Previous development efforts have produced versions of EPREM designed to ingest output from specific MHD models but there is currently no single version of EPREM that can ingest arbitrary MHD information.

EPREM accepts user arguments to a variety of simulation parameters via a text file, passed on the command line at runtime. All simulation parameters have default values.

The primary EPREM output product is a set of data files in NetCDF (.nc) format. In the standard operational mode, there is one file per stream of nodes. Each file contains both static and time-dependent arrays of simulated physical quantities. The static arrays include mass and charge of each simulated species, and velocity and energy bins per species. The time-dependent arrays include the 3D spherical coordinates of each node, the 3D spherical components of the magnetic and velocity fields at each node, and the plasma density at each node. By default, each file also contains the pitch-angle resolved distribution function at each node; a runtime argument allows the user to request the pitch-angle averaged flux instead.