RTE+RRTMGP

This is the repository for RTE+RRTMGP, a set of codes for computing radiative fluxes in planetary atmospheres. RTE+RRTMGP is described in a paper in Journal of Advances in Modeling Earth Systems.

RRTMGP uses a k-distribution to provide an optical description (absorption and possibly Rayleigh optical depth) of the gaseous atmosphere, along with the relevant source functions, on a pre-determined spectral grid given temperatures, pressures, and gas concentration. The k-distribution currently distributed with this package is applicable to the Earth's atmosphere under present-day, pre-industrial, and 4xCO2 conditions.

RTE computes fluxes given spectrally-resolved optical descriptions and source functions. The fluxes are normally summarized or reduced via a user extensible class.

Example programs and documentation are evolving - please see examples/ in the repo and Wiki on the project's Github page. Suggestions are welcome. Meanwhile for questions please contact Robert Pincus and Eli Mlawer at rrtmgp@aer.com.

Recent changes

1. The default method for solution for longwave problems that include scattering has been changed from 2-stream methods to a re-scaled and refined no-scattering calculation following Tang et al. 2018.
2. In RRTMGP gas optics, the spectrally-resolved solar source function in can be adjusted by specifying the total solar irradiance (gas_optics%set_tsi(tsi)) and/or the facular and sunspot indicies (gas_optics%set_solar_variability(mg_index, sb_index, tsi))from the NRLSSI2 model of solar variability.
3. rte_lw() now includes optional arguments for computing the Jacobian (derivative) of broadband flux with respect to changes in surface temperature. In calculations neglecting scattering only the Jacobian of upwelling flux is computed. When using re-scaling to account for scattering the Jacobians of both up- and downwelling flux are computed.
4. A new module, mo_rte_config, contains two logical variables that indicate whether arguments to routines are to be checked for correct extents and/or valid values. These variables can be changed via calls to rte_config_checks(). Setting the values to .false. removes the checks. Invalid values may cause incorrect results, crashes, or other mayhem

Relative to commit 69d36c9 to master on Apr 20, 2020, the required arguments to both the longwave and shortwave versions of ty_gas_optics_rrtmgp%load()have changed.

Building the libraries, examples, and unit-testing codes.

1. Set environment variables FC (the Fortran 2003 compiler) and FCFLAGS (compiler flags). Examples are provided in the Compiler-flags.md file.
2. Set environment variables RRTMGP_ROOT to the top-level RTE+RRTMGP directory and RTE_KERNELS to openacc if you want the OpenACC/OpenMP kernels rather than the default.
3. make libs in the top-level directory will make the RTE and RRTMGP libraries.
4. The examples and testing codes use netCDF. Set the variables NCHOME and NFHOME to the roots of the C and Fortran netCDF installations, then make tests to build and run these. (A few files need to be downloaded for examples/rfmaip-clear-sky. The default is to download these with wget but a Python script is also available.)
5. Evaluating the results of the tests requires Python with the xarray package and its depdencies installed. Comparisons can be made with make check in the top level directory.
6. make invoked without a target in the top level attempts all three steps.

Examples

Two examples are provided in examples/, one for clear skies and one including clouds. Directory tests/ contains regression testing (e.g. to ensure that answers are independent of orientation) and unit testing (to be sure all the code paths are tested). See the README file and codes in each directory for further information.