RRTMG_LW What's New:

Validation results of latest version of RRTMG_LW relative to LBLRTM.

RRTMG_LW v5.00

Date: March 2020

• Two new cloud overlap options were added: i) exponential (icld=4) and ii) exponential-random (icld=5) that apply an exponential transition from maximum to random through model layers. Exponential applies this transition through all layers without regard to the cloud configuration and exponential-random applies this transition through adjacent cloudy layers while randomly correlating cloud layers separated by clear sky. Both methods require calling a new subroutine, get_alpha, to define alpha, the exponential transition parameter, prior to calling the McICA sub-column generator. Alpha requires the specification of a decorrelation length (in meters), and two methods for defining this value are available that are selected using a new input control variable, idcor, that allows the decorrelation length to be specified either as a constant or as a value that varies by latitude and day-of-year using the method of Oreopolous et al. (2012). See the file doc/rrtmg_lw_instructions.txt for more information.

RRTMG_LW v4.91

Date: November 2017

• Removed the "/src/src_link" script that previously linked to the RRTM versions of rrtatm.f and extra.f. Current versions of those files as of this release have been added to this repository in the /src directory. The values of MXLAY and MXMOL were also updated to correspond with those now used in rrtatm.f. Removed the "/src/util_link" script that previously linked to the utility files and relocated these to a new /aer_rt_utils folder that is tied to ~/RD/AER_RT_UTILS/trunk in the svn repository as an external. All provided makefiles have been updated to get the utility files from the new directory.

RRTMG_LW v4.90

Date: September 2016

• All source code modules were modified to replace the original copyright statement with a new BSD 3-clause software license (at the request of ECMWF). Additional minor changes include: - Changed declaration of variable cinp in subroutine readprof in file rrtmg_lw.1col.f90 from implicit real to character*3. - Fixed integer kind type problem in file rrtmg_lw_read_nc.f90 by replacing all numeral "1" arguments to nf90_get_var to "1_im" to prevent errors on some compilers. - Added fix to original two-layer memory cloud overlap method in source file rrtmg_lw_rtrnmr.f90. This replaces the previous formulations for variables faccmb1, faccmb2, faccmb1d, and faccmb2d.

RRTMG_LW v4.85

Date: November 2011

• A minor fix has been made to rrtmg_lw_taumol.f90 to the code introduced in v4.82 to correct 'specparm' to read 'specparm1' at line 1513 in band 7. This change has no impact in moderate to high moisture profiles such as mid-latitude summer and tropical. The largest impact will occur in cold, dry profiles such as mid-latitude winter, or sub-arctic winter. In these profiles, the impact is generally less than 0.05 Wm-2 in flux and less than 0.06 Kd-1 in heating rate. Other minor changes were made to improve code compatibility with g95 compilers that have no effect on output.

RRTMG_LW v4.84

Date: November 2009

• An optional feature has been added to the model to provide the vertical profile of the change in upward flux with respect to surface temperature. This option is controlled by a new input flag, idrv. Setting this flag to 1 will output dF/dT for total sky and clear sky in GCM mode in the new output arrays duflx_dt and duflxc_dt. These can be utilized to approximate the change in upward flux for a change in surface temperature only and to derive approximate changes in layer heating rate at time intervals between full radiation calls. This feature should be used in a GCM with some caution, since large changes to only the surface temperature and emission while leaving the atmosphere unchanged will alter the flux divergence and heating in the near surface layers to a degree that may disrupt the GCM simulation. In single column mode, setting idrv to 1 requires the additional input of a dT change in surface temperature relative to the input surface temperature, and the provided dT will be applied to the flux derivative to output a modified upward flux profile for that dT change in surface temperature. Setting idrv to 0 provides the original forward radiative transfer calculation.

RRTMG_LW v4.82

Date: October 2009

• Installed code fix to module rrtmg_lw_taumol.f90 to revise definition and use of the key species ratio parameter (eta) in some spectral bands. Results are changed in profiles with low water vapor and low temperature. Downward surface fluxes are typically increased by this change by about 0.1 W m-2, with downward flux in some layers increased by as much as 0.5 W m-2 in some profiles. Upward flux changes are smaller. Heating rate changes are generally negligible. There are no changes in flux or heating rate in profiles with moderate to high water vapor such as mid-latitude summer or tropical.

RRTMG_LW v4.8

Date: May 2009

• New option added to input absorption coefficient data either through original source statements or through a netCDF data file. Choice of input source is selected in the makefile. This feature was developed and contributed by Patrick Hofmann and Robert Pincus of NOAA.


• Added fix for internal cloud property option (iceflag=1) to correct the integer index that accesses the input coefficient arrays that are used to calculate the ice cloud absorption for this option. Other cloud optical property options are unaffected.


• Minor code changes were made to allow the model to compile and run under single precision.


• The lower bound of allowable liquid droplet effective radius was changed from 1.5 to 2.5 microns for the inflag=2/liqflag=1 cloud input option.

RRTMG_LW v4.71

Date: September 2008

• Modified input of ice particle effective size to require input of value appropriate for the selected ice optics parameterization. Previous scaling that was applied internally to convert ice effective radius to generalized effective size for the Fu parameterization has been removed. Any necessary scaling needed to provide the proper ice particle size must be done before input to the radiation in the GCM version of the code. This is consistent with the input requirement for the column version of the model. Note that the internal ice optics parameterizations are effective over specific ranges of particle size. Results may be different from previous versions if the Fu parameterization is used in the GCM version of the code. Also, fixed the definition of the secant of the diffusivity angle, which varies as a function of the water column amount. This change only affects results in profiles with more than eight precipitable cm of water vapor.

RRTMG_LW v4.7

Date: August 2008

• Added requirement that cloud liquid and ice water paths, or optionally the cloud optical depth, be input as in-cloud averages rather than grid-averaged values in the version of the code intended for use in a GCM. This change requires that these cloud properties be scaled by the cloud fraction on input to convert to in-cloud values if necessary. The column model version of the code continues to expect in-cloud values as before. Oxygen amount was changed from being defined internally to a required input. Several other cosmetic modifications do not affect results, but a change in the factor used to convert flux to heating rate from a fixed to a calculated quantity may produce negligible differences in heating rates.

RRTMG_LW v4.5

Date: April 2008

• Added capability to treat longwave aerosol absorption and added use of input file IN_AER_RRTM to read in aerosol optical depths following the application of this file in RRTMG_SW. Aerosol scattering is not presently available in the longwave, so the required input is limited to the aerosol optical depth by layer at the mid-point of each of the 16 spectral bands.

RRTMG_LW v4.4

Date: September 2007

• Modified use of ice particle size variables rei/reicmc to utilize separate variable names (dge/dgesmc) when units of generalized effective size are required for Fu ice parameterization (iceflag=3) option. Results may be minimally affected when ice particle radii exceed 90 microns and the iceflag=3 option is used. Also modified several local arrays in top-level subroutine module to accomodate an extra model layer at the top of the atmosphere if this feature is utilized when using the code in a GCM.

RRTMG_LW v4.3

Date: August 2007

• Includes changes to the makefile for AIX systems and a few minor fixes in the interface for the subroutine version of the model. Results are identical to the previous version.

RRTMG_LW v4.1

Date: August 2007

• Includes several format changes to retain consistency with RRTMG_SW. Results are identical to the previous version.

RRTMG_LW v4.0.2

Date: May 2007

• Made several minor adjustments to kind type suffixes in several modules and made changes to the README file. Results are identical to the previous version.

RRTMG_LW v4.0.1

Date: April 2007

• Includes minor bug fix to the dimension of arrays abscoice and abscoliq in rrtmg_lw_cldprmc.f90, which affected results on some compilers.

RRTMG_LW v4.0

Date: April 2007

• Major source code reformatting to utilize modern FORTRAN90 features such as modules. Older common blocks have been removed from all but I/O related source files to retain I/O compatibility with RRTM.


• Model can be run as a stand-alone column model using the same I/O format as RRTM and LBLRTM, or it can be used as a callable subroutine and implemented within a global or regional model.


• McICA (Monte Carlo Independent Column Approximation) capabililty added for representation of sub-grid cloud variability such as cloud fraction and cloud overlap.


• Includes two options for the random number generator needed for McICA.


• Sample makefiles for several computer platforms are provided.


• Sample input and output files and instructions for the input files are also included in the source package.