This repository contains code to run the ECHAM6 radiative transfer offline. It mostly consists of Fortran code that has been copied from the model source code and has only been slightly adapted to run without the host model. There are two options to interface the radiative transfer code, one directly via a Fortran and one via a Python wrapper into the Fortran source code. It nevertheless is strongly recommended to use the Python wrapper.

The FORTRAN code has to be compiled with the netCDF and the MPICH library. They should be present on some machines (e.g. on LIM/DKRZ servers). If not, those libraries can be installed via conda.

If you use conda, first set up an environment:

conda env create -f environment.yml
conda activate echam_radiation_offline

After installing the libraries, you need to give the path to your newly created environment in build/Makeinclude_fc. For this you need to set CONDA_BASE_PATH. To find this directory, use a which python and remove the bin/python at the end output of this command).

To compile the Fortran code and the Python wrapper, change to the build directory and enter make clean && make all.

An example of how to use the Python wrapper can be found in scripts/prp_python.py. The following variables are needed to run the radiative transfer code:

land-sea mask, glacier mask, surface pressure, cloud water, cloud ice, relative humidity, surface albedo, cloud cover (3D), ozone concentration, surface temperature, air temperature, specific humidity

Furthermore, the pressure (pf) of the midpoints of the vertical levels, as well as the pressure at the interfaces of the vertical levels (ph) is needed. If cloud droplet number is available, it can be used. If this variable is not present, set cdnc_cal to True and it will be calculated within the Fortran code using the default profile of ECHAM6.