RRTM_LW: What's new
results of latest version of RRTM relative to LBLRTM.
Date: May 2010
- Updated water vapor continuum absorption coefficients are consistent with those in MT_CKD 2.5.
- Scattering capability is available through the radiative transfer solver DISORT [Stamnes et al., 1988].
- Ice cloud scattering optical properties for the Fu et al. 
parameterization (hexagonal particles) and for the STREAMER v3.0 code
(spherical particles) have been included.
- Options for users to directly input cloud and aerosol absorption
and scattering optical properties have been expanded (INFLAG
equals 0 or 10 in IN_CLD_RRTM file).
- Output file (OUT_CLD_RRTM) containing cloud optical properties used in model calculation is now generated.
- Code fix to taumol.f to revise use of the binary species
parameter 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 m2 in some profiles, upward flux changes are smaller.
- Updated physical constants to be consistent with NIST .
- Updated the atmospheric ray trace program (rrtatm) to be consistent with LBLRTM v11.7.
- Updated formatting in the OUTPUT_RRTM file.
- Single makefile applies for a wide range of computing platforms.
Date: Sept 2002
Identical to v3.0 except for minor changes to the makefiles provided with
the distribution of RRTM.
The RRTM source code is identical between release v3.0 and release v3.01.
Date: August 2002
The following are descriptions
of important changes contained in RRTM v3.0:
The line parameters for species other than water vapor were obtained from
HITRAN 1996 database (http://www.hitran.com). The water vapor lines from
500.0 to 2880. cm-1 were replaced with those measured by Dr.
Bob Toth (JPL).These parameters
for water vapor are consistent with the HITRAN 2000 database.Line
coupling coefficients have been utilized for the important Q-branches ofcarbon
dioxide.These line coupling coefficients
have been updated for consistency with the HITRAN 1996 carbon dioxide line
The water vapor continuum absorption coefficients were obtained from CKD
2.4.Note that contributions to the
optical depth from both the self and foreign water vapor continuum are
now explicitly calculated.Continuum
contributions from nitrogen are now included.
RRTM calculates fluxes and cooling rates in the longwave spectral region
(from 10 to 3250 cm-1).Note
that in the previous version, RRTM v2.3, the spectral region extended only
to 3000 cm-1.
The errors in computed stratospheric cooling rates have been substantially
reduced.In RRTM v3.0 the average
maximum stratospheric cooling rate error (for a representative set of 43
atmospheric profiles) is 0.27 K/day, compared with an average error of
0.53 K/day for RRTM v2.3.
The fluxes and cooling rates computed in RRTM v3.0 are greatly improved
for atmospheres having abundances of trace gases (e.g. CO2,
CH4) substantially different from current abundances.
Cloudy-sky radiative transfer calculations include new options:
Radiative transfer algorithms
for cloudy layers with random or maximum/random overlap.
Ice particle parameterization
from Fu, Yang, and Sun (J. Climate, Vol 11, 1998, pp. 2223 - 2237).
Capability to input atmospheric profile on either altitude or pressure
grid, and to output quantities on either altitude or pressure grid.
The source function in each layer is now computed using the exact linear
in tau approach, in contrast to the use of a Pade approximant in RRTM v2.3.Both
the exponential function and the exact 'linear in tau' function are tabulated
at 5000 values and a table lookup is used in the radiative transfer calculation.It
should be noted that this adds a small element of discreteness into the
calculation. (This methodology is consistent with LBLRTM v6.0.)
Makefiles for creating single precision executables for a number of platforms
have been included.
A set of sample RRTM input files has been included in the tar file in a
directory called /sample_runs/.
The instruction manual has been updated.It
includes important changes to many options, such as the number of angles
used in the flux calculations, the declaration of either random or maximum/random
cloud overlap assumption etc.
Atmospheric and Environmental Research