RRTMG_SW: Shortwave Radiative Transfer Model for GCMs

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Contents

1. Introduction
2. Releases
3. Column Version
4. GCM Version
5. Contact
6. References

Introduction

This package contains the source code and sample makefiles necessary to run the latest version of RRTMG_SW, a correlated k-distribution shortwave radiative transfer model developed at AER for application to GCMs. This version of RRTMG_SW utilizes a two-stream radiative transfer method as implemented at ECMWF. This code has also been modified to utilize updated FORTRAN coding features. Two modes of operation are possible:

1. RRTMG_SW can be run as a column model using the input files and source modules described in the column version section, or
2. it can be implemented as a subroutine into an atmospheric general circulation model or single column model.

The version of RRTMG_SW provided here utilizes a reduced complement of 112 g-points, which is half of the 224 g-points used in the standard RRTM_SW, and a two-stream method for radiative transfer. Additional minor changes have been made to enhance computational performance. Total fluxes are accurate to within 1-2 W m^-2 relative to the standard RRTM_SW (using DISORT) in clear sky and in the presence of aerosols and within 6 W m^-2 in overcast sky. RRTM_SW with DISORT is itself accurate to within 2 W m^-2 of the data-validated multiple scattering model, CHARTS. Required absorption coefficient input data can be read in either from data stored within the code or from a netCDF file as selected in the makefile.

This model can also utilize McICA, the Monte-Carlo Independent Column Approximation, to represent sub-grid scale cloud variability such as cloud fraction and cloud overlap. If the McICA option is selected to model a cloudy profile in column mode, then the model will run stochastically, and the output fluxes and heating rates will be an average over 200 samples. In GCM mode, the code will calcualte a single column per profile, and the statistical basis is provided by the spatial and temporal dimensions of the 3-D calculations. Several cloud overlap methods are available for partial cloudiness including maximum-random, exponential, and exponential-random. Without McICA, RRTMG_SW is limited to clear sky or overcast cloud conditions.

For more information on the model, see the Wiki Description Page.

Current Release

Version 5.0 is the latest version of the model

Releases before Version 5.0 are not publicly available.

RRTMG_SW : Column Version

DOCUMENTATION

The following text files (in the doc directory), along with this README provide information on release updates and on using and running RRTMG_SW:

File Name	Description
release_notes.txt	Code archive update information
rrtmg_sw_instructions.txt	Input instructions for files INPUT_RRTM, IN_CLD_RRTM and IN_AER_RRTM

SOURCE CODE

The following source files (in the src directory) must be used to run RRTMG_SW in stand-alone mode as a column model (the utility files are stored separately in the aer_rt_utils directory):

File Name	Description
rrtmg_sw.1col.f90	Main module
rrtmg_sw_cldprop.f90	Calculation of cloud optical properties
rrtmg_sw_cldprmc.f90	Calculation of cloud optical properties (McICA)
rrtmg_sw_init.f90	RRTMG_SW initialization routine; reduces g-intervals from 224 to 112
rrtmg_sw_k_g.f90	Absorption coefficient data file
rrtmg_sw_read_nc.f90	Optional absorption coefficient data netCDF input
rrtmg_sw_reftra.f90	Calculation of two-stream reflectivities and transmissivities
rrtmg_sw_setcoef.f90	Set up routine
rrtmg_sw_spcvrt.f90	Top subroutine for two-stream model
rrtmg_sw_spcvmc.f90	Top subroutine for two-stream model (McICA)
rrtmg_sw_taumol.f90	Calculation of optical depths and Planck fractions for each spectral band
rrtmg_sw_vrtqdr.f90	Two-stream vertical quadrature
mcica_random_numbers.f90	Random number generator for McICA
mcica_subcol_gen_sw.1col.f90	Sub-column generator for McICA
rrtatm.f	Process user-defined input data files
extra.f	Process input data files
util_**.f	Utilities (available for multiple platforms)

The following module files (in the modules directory) must be used to run RRTMG_SW in stand-alone mode as a column model (these must be compiled before the source code files):

File Name	Description
parkind.f90	real and integer kind type parameters
parrrsw.f90	main configuration parameters
rrsw_aer.f90	aerosol property coefficients
rrsw_cld.f90	cloud property coefficients
rrsw_con.f90	constants
rrsw_kg**.f90	absorption coefficient arrays for 16 spectral bands
rrsw_ncpar.f90	parameters for netCDF input data option
rrsw_ref.f90	reference atmosphere data arrays
rrsw_tbl.f90	exponential lookup table arrays
rrsw_vsn.f90	version number information
rrsw_wvn.f90	spectral band and g-interval array information

INPUT DATA

The following file (in the data directory) is the optional netCDF input file containing absorption coefficient and other input data for the model. The file is used if keyword KGSRC is set for netCDF input in the makefile.

File Name	Description
rrtmg_sw.nc	Optional netCDF input data file

MAKEFILES

The following files (in build/makefiles directory) can be used to compile RRTMG_SW in stand-alone mode as a column model on various platforms. Link one of these into the build directory to compile.

File Name	Description
make_rrtmg_sw_sgi	Sample makefile for SGI
make_rrtmg_sw_sun	Sample makefile for SUN
make_rrtmg_sw_linux_pgi	Sample makefile for LINUX (PGI compiler)
make_rrtmg_sw_aix_xlf90	Sample makefile for AIX (XLF90 compiler)
make_rrtmg_sw_OS_X_g95	Sample makefile for OS_X (G95 compiler)
make_rrtmg_sw_OS_X_ibm_xl	Sample makefile for OS_X (IBM XL compiler)

SAMPLE INPUT/OUTPUT

Several sample input (and output) files are included in the run_examples_std_atm directory. Note that user-defined profiles may be used for as many as 200 layers.

File Name	Description
INPUT_RRTM	Required input file for (clear sky) atmospheric specification
IN_CLD_RRTM	Required input file for cloud specification if clouds are present
IN_AER_RRTM	Required input file for aerosol specification if aerosols are present
OUTPUT_RRTM	Main output file for atmospheric fluxes and heating rates
input_rrtm.MLS-clr	Sample 51 layer mid-latitude summer standard atmosphere
input_rrtm.MLS-cld-imca0-icld2	Sample 51 layer mid-latitude summer standard atmosphere with cloud flag turned on and maximum-random cloud overlap selected (without McICA)
input_rrtm.MLS-cld-imca1-icld2	Sample 51 layer mid-latitude summer standard atmosphere with cloud flag turned on and maximum-random cloud overlap selected (with McICA)
input_rrtm.MLS-cld-imca1-icld5-idcor0	Sample 51 layer mid-latitude summer standard atmosphere with cloud flag turned on and exponential-random cloud overlap and constant decorrelation length selected (with McICA)
input_rrtm.MLS-cld-imca1-icld5-idcor1	Sample 51 layer mid-latitude summer standard atmosphere with cloud flag turned on and exponential-random cloud overlap and varying decorrelation length selected (with McICA)
input_rrtm.MLS-clr-aer12	Sample 51 layer mid-latitude summer standard atmosphere with aerosol flag set
input_rrtm.MLS-clr-sza45-isolvar0_tsi_avg	Sample 51 layer mid-latitude summer standard atmosphere with solar zenith angle set to 45 degrees and using the NRLSSI2 solar source function with total solar irradiance for the mean solar cycle with no solar variability
input_rrtm.MLS-clr-sza45-isolvar1_tsi_max	Sample 51 layer mid-latitude summer standard atmosphere with solar zenith angle set to 45 degrees and using the NRLSSI2 solar source function with solar variability active and with total solar irradiance near the maximum in the mean solar cycle
input_rrtm.MLS-clr-sza45-isolvar1_tsi_min	Sample 51 layer mid-latitude summer standard atmosphere with solar zenith angle set to 45 degrees and using the NRLSSI2 solar source function with solar variability active and with total solar irradiance near the minimum in the mean solar cycle
input_rrtm.MLS-clr-sza45-isolvar2_01Jan1950	Sample 51 layer mid-latitude summer standard atmosphere with solar zenith angle set to 45 degrees and using the NRLSSI2 solar source function with solar variability active and with total solar irradiance specified with facular and sunspot indices for 1 January 1950
input_rrtm.MLS-clr-sza45-isolvar3_bndscl_tsi_max	Sample 51 layer mid-latitude summer standard atmosphere with solar zenith angle set to 45 degrees and using the NRLSSI2 solar source function with solar variability active and with total solar irradiance near the maximum in the mean solar cycle scaled to a different value with individual band scaling factors
input_rrtm.MLW-clr	Sample 51 layer mid-latitude winter standard atmosphere
input_rrtm.SAW-clr	Sample 51 layer sub-arctic winter standard atmosphere
input_rrtm.TROP-clr	Sample 51 layer tropical standard atmosphere
in_cld_rrtm-cld5	Sample cloud input file
in_cld_rrtm-cld6	Sample cloud input file
in_cld_rrtm-cld7	Sample cloud input file
in_aer_rrtm-aer12	Sample aerosol input file
script.run_std_atm	UNIX script for running the full suite of example cases, which will put the output into similarly named files prefixed with output_rrtm*

INSTRUCTIONS FOR COMPILING AND RUNNING THE COLUMN MODEL:

1. In the build directory, link one of the makefiles from the makefile sub-directory into build/make.build. To use the optional netCDF input file, switch the keyword KGSRC in the makefile from dat to nc. Compile the model with make -f make.build
2. Link the executable to, for example, rrtmg_sw in the run_examples_std_atm directory
3. If the optional netCDF input file was selected when compiling, link the file data/rrtmg_sw.nc into the run_examples_std_atm directory.
4. In the run_examples_std_atm directory, run the UNIX script ./script.run_std_atm to run the full suite of example cases. To run a single case, modify INPUT_RRTM following the instructions in doc/rrtmg_sw_instructions.txt, or copy one of the example input_rrtm* files into INPUT_RRTM. If clouds are selected (ICLD > 0), then modify IN_CLD_RRTM or copy one of the in_cld_rrtm* files into IN_CLD_RRTM. If aerosols are selected (IAER > 0), then modify IN_AER_RRTM or set it to the sample file in_aer_rrtm-aer12.
5. In column mode, if McICA is selected (IMCA=1) with partial cloudiness defined, then RRTMG_SW will run the case 200 times to derive adequate statistics, and the average of the 200 samples will be written to the output file, OUTPUT_RRTM.

RRTMG_SW : GCM version

SOURCE CODE

The following source files (in the src directory) must be used to run RRTMG_SW as a callable subroutine:

File Name	Description
rrtmg_sw_rad.f90	RRTMG_SW main module (with McICA)
rrtmg_sw_rad.nomcica.f90	Optional RRTMG_SW main module (without McICA only)
rrtmg_sw_cldprop.f90	Calculation of cloud optical properties
rrtmg_sw_cldprmc.f90	Calculation of cloud optical properties (McICA)
rrtmg_sw_init.f90	RRTMG_SW initialization routine; reduces g-intervals from 224 to 112; (This has to run only once and should be installed in the GCM initialization section)
rrtmg_sw_k_g.f90	Absorption coefficient data file
rrtmg_sw_read_nc.f90	Alternate absorption coefficient data netCDF input
rrtmg_sw_reftra.f90	Calculation of two-stream reflectivities and transmissivities
rrtmg_sw_setcoef.f90	Set up routine
rrtmg_sw_spcvrt.f90	Top subroutine for two-stream model
rrtmg_sw_spcvmc.f90	Top subroutine for two-stream model (McICA)
rrtmg_sw_taumol.f90	Calculation of optical depths and Planck fractions for each spectral band
rrtmg_sw_vrtqdr.f90	Two-stream vertical quadrature
mcica_random_numbers.f90	Random number generator for McICA
mcica_subcol_gen_sw.f90	Sub-column generator for McICA

NOTE: Only one of rrtmg_sw_k_g.f90 or rrtmg_sw_read_nc.f90 is required.

The following module files (in the modules directory) must be used to run RRTMG_SW as a callable subroutine (these must be compiled before the source code)

File Name	Description
parkind.f90	real and integer kind type parameters
parrrsw.f90	main configuration parameters
rrsw_aer.f90	aerosol property coefficients
rrsw_cld.f90	cloud property coefficients
rrsw_con.f90	constants
rrsw_kg**.f90	absorption coefficient arrays for 16 spectral bands
rrsw_ncpar.f90	parameters for netCDF input data option
rrsw_ref.f90	reference atmosphere data arrays
rrsw_tbl.f90	exponential lookup table arrays
rrsw_vsn.f90	version number information
rrsw_wvn.f90	spectral band and g-interval array information

INPUT DATA

The following file (in the data directory) is the optional netCDF file containing absorption coefficient and other input data for the model. The file is used if source file rrtmg_sw_read_nc.f90 is used in place of rrtmg_sw_k_g.f90 (only one or the other is required).

File Name	Description
rrtmg_sw.nc	Optional netCDF input data file

NOTES ON RUNNING THE GCM (SUBROUTINE) VERSION OF THE CODE

1. The module rrtmg_sw_init.f90 is the initialization routine that has to be called only once. The call to this subroutine should be moved to the initialization section of the host model if RRTMG_SW is called by a GCM or SCM.
2. The number of model layers and the number of columns to be looped over should be passed into RRTMG_SW through the subroutine call along with the other model profile arrays.
3. To utilize McICA, the sub-column generator (mcica_subcol_gen_sw.f90) must be implemented in the GCM so that it is called just before RRTMG_SW. The cloud overlap method is selected using the input flag, icld. If either exponential (ICLD=4) or exponential-random (ICLD=5) cloud overlap is selected, then the subroutine get_alpha must be called prior to calling mcica_subcol_sw to define the vertical correlation parameter, alpha, needed for those overlap methods. Also for those methods, use the input flag idcor to select the use of either a constant or latitude-varying decorrelation length. If McICA is utilized, this will run only a single statistical sample per model grid box. There are two options for the random number generator used with McICA, which is selected with the variable irnd in mcica_subcol_gen_sw.f90. When using McICA, then the main module is rrtmg_sw_rad.f90. If McICA is not used, then the main module is rrtmg_sw_rad.nomcica.f90, though the cloud specification is limited to overcast clouds.

Maintenance and Contact Info

Atmospheric and Environmental Research 131 Hartwell Avenue, Lexington, MA 02421

Original version: Eli. J. Mlawer, J. S. Delamere, et al. (AER) Revision for GCMs: Michael J. Iacono (AER)

Contact: Michael J. Iacono (E-mail: miacono@aer.com)

References

• AER Radiative Transfer Models Documentation
• Github Wiki
• RRTMG_SW, RRTM_SW
  • Iacono, M.J., J.S. Delamere, E.J. Mlawer, M.W. Shephard, S.A. Clough, and W.D. Collins, Radiative forcing by long-lived greenhouse gases: Calculations with the AER radiative transfer models, J. Geophys. Res., 113, D13103, doi:10.1029/2008JD009944, 2008.
  • Clough, S.A., M.W. Shephard, E.J. Mlawer, J.S. Delamere, M.J. Iacono, K. Cady-Pereira, S. Boukabara, and P.D. Brown, Atmospheric radiative transfer modeling: a summary of the AER codes, J. Quant. Spectrosc. Radiat. Transfer, 91, 233-244, 2005.
• McICA
  • Pincus, R., H. W. Barker, and J.-J. Morcrette, A fast, flexible, approximation technique for computing radiative transfer in inhomogeneous cloud fields, J. Geophys. Res., 108(D13), 4376, doi:10.1029/2002JD003322, 2003.
• Latitude-Varying Decorrelation Length
  • Oreopoulos, L., D. Lee, Y.C. Sud, and M.J. Suarez, Radiative impacts of cloud heterogeneity and overlap in an atmospheric General Circulation Model, Atmos. Chem. Phys., 12, 9097-9111, doi:10.5194/acp-12-9097-2012, 2012.
• Full list of references