As part of the Intercomparison of Three-dimensional Radiative Transfer Codes (I3RC) effort, we have developed a Monte Carlo radiative transfer. This freely-available, modifiable code is intended to be fast enough to use in significant research applications, clear enough to be useful as a teaching tool, and extensible enough to be easily modified for specific needs.

The package embodies best practices in both the simulation of radiative transfer and the coding methodology. The framework allows for consistent representation of any number of radiative components in the atmosphere, a variety of surface types, and uniform configuration and results reporting. It is written in highly-structured Fortran 90 and is portable and straightforward to parallelize. Integrators are provided for computing domain-averaged fluxes using photon-tracing and maximal cross-section methods, but other integrators could be written to compute other quantities (radiances, heating rates, pathlength distributions) at other resolutions (pixel-by-pixel, layer by layer). The code is being tested on a suite of 3D cloud cases defined by the I3RC project (see http://i3rc.gsfc.nasa.gov).We will continue to develop the package’s capabilities, and will gladly distribute components developed by others.