This directory contains the main part of the radiation scheme except
for the calculation of gas optics.  It is compiled into static library
../lib/libradiation.a and module files ../mod/radiation_*.mod. The
coding conventions are described in the CONVENTIONS file.  See the
file ../driver/radiation_driver.f90 for an example of how the
radiation scheme is called. The code is arranged as follows.

The configuration information for the radiation scheme is stored in a
"config" object (type defined in *radiation_config.f90*).  After this
has been populated depending on how the radiation scheme is to be
configured, the subroutine "setup_radiation" in
*radiation_interface.f90* is called.  This sets up the gas, cloud and
aerosol optics, all of which involve reading data from NetCDF files.
The cloud and aerosol optics data are described in
*radiation_aerosol_optics_data.f90* and
*radiation_cloud_optics_data.f90*.

The main interface to the radiation scheme is via the "radiation"
subroutine in radiation_interface.f90, which takes six objects as
input (noting that multiple columns are processed at once):

  single_level - all single-level fields such as skin temperature and
      surface albedo (type defined in *radiation_single_level.f90*)

  thermodynamics - pressure and temperature (type defined in
      *radiation_thermodynamics.f90*)

  gas - mixing ratios of gases (type defined in *radiation_gas.f90*)

  cloud - cloud fraction, water content and other information (type
      defined in *radiation_cloud.f90*)

  aerosol - mixing ratios of different aerosol species (type defined
      in *radiation_aerosol.f90*)

The output is stored in the following object:

  flux - upwelling and downwelling shortwave and longwave fluxes (type
      defined in *radiation_flux.f90*)

The "radiation" subroutine first computes the gas optical properties
(in the form of 3D arrays of dimension column, height and spectral
g-point), via a call to the "gas_optics" subroutine in
*radiation_ifsrrtm.f90*, which provides an interface to the IFS
implementation of the RRTM-G gas optics model in the ../ifsrrtm
directory.  For testing, a simple monochromatic gas model is also
provided in *radiation_monochromatic.f90*.

To these fields are added the contribution from aerosols via a call to
the "aerosol_optics" subroutine, from *radiation_aerosol_optics.f90*.

Cloud optical properties are computed (in the form of 3D arrays of
dimension column, height and spectral band), via a call to the
"cloud_optics" subroutine in *radiation_cloud_optics.f90*.

The optical properties may then be saved to an intermediate NetCDF
file via a routine in *radiation_save.f90*.

Finally, the optics data are passed to the solver, which computes the
flux profiles.  Currently McICA nad SPARTACUS solvers are
available. In the case of SPARTACUS, the longwave and shortwave
versions are in *radiation_spartacus_lw.f90* and
*radiation_spartacus_sw.f90*, respectively.  These make use of
routines in the following files:

  *radiation_two_stream.f90* - compute two-stream coefficients

  *radiation_matrix.f90* - matrix operations needed by SPARTACUS

  *radiation_overlap.f90* - compute cloud overlap matrices.

Physical constants are provided in *radiation_constants.f90*.