Key features of RRTMG_SW are:
Absorption coefficient data for the k-distributions are obtained directly from the
line-by-line radiative transfer model, LBLRTM,
which has been extensively validated against observations, principally at the
ARM SGP site. Data are consistent with those used in RRTM_SW_v2.5, which is
Fluxes and heating rates can be calculated over fourteen contiguous bands in the
shortwave (820-50000 cm-1, or 0.2-12.20 microns). The individual band
ranges (in wavenumbers, cm-1) are: 2600-3250, 3250-4000, 4000-4650,
4650-5150, 5150-6150, 6150-7700, 7700-8050, 8050-12850, 12850-16000, 16000-22650,
22650-29000, 29000-38000, 38000-50000, and 820-2600. The last band is coded out
of sequence to preserve spectral continuity with the longwave bands.
Modeled sources of extinction are water vapor, carbon dioxide, ozone,
methane, oxygen, nitrogen, aerosols, and Rayleigh scattering
A two-stream algorithm is used to perform scattering calculations; Reference:
Oreopoulos and Barker (1999).
Uses reduced set of g-intervals (112) for integration over extinction in
each band relative to full set of g-intervals used in RRTM_SW (224).
Includes McICA (Monte-Carlo Independant Column Approximation) capability
to represent sub-grid cloud variability with random, maximum-random,
maximum, exponential, and exponential-random options for cloud overlap;
the exponential and exponential-random methods allow specification of the
required decorrelation length as a constant or as a variable that varies
as a function of latitude and day of the year; References: Barker et al.
(2003); Pincus et al., JGR, (2003); Oreopoulos et al., ACP, (2012)
Coding has been reformatted to use many FORTRAN90 features.
Model able to run either as a column model or as a callable subroutine.
Clear sky agreement with RRTM_SW is generally within 3 W/m2 for flux
and for heating rate within 0.1 K/d in the troposphere and 0.3 K/d in the
The optical properties of water clouds are calculated for each spectral
band from the Hu and Stamnes parameterization. The optical depth,
single-scattering albedo, and asymmetry parameter are parameterized as
a function of cloud equivalent radius and liquid water path.
Reference: Hu, Y. X., and K. Stamnes, An accurate parameterization
of the radiative properties of water clouds suitable for use in climate
models. J. Climate, Vol. 6, 728-742, 1993.
The optical properties of ice clouds are calculated for each spectral band
from the Fu parameterization, which assumes the ice crystals are hexagonal
and randomly-oriented in space. The optical depth, single-scattering
albedo, and asymmetry parameter are parameterized as a function of the
generalized effective size of the ice crystals and the ice water content.
(It is important to note that the generalized effective size is not equivalent
to the effective mean size.)
Reference: Fu, Q., An accurate parameterization of the
solar radiative properties of cirrus clouds for climate models. J.
Climate, 9, 2058-2082, 1996.
Absorption coefficients, solar source function, and other initialization data
(provided by default within the code) can be optionally input through a netCDF
data file. This feature was developed and provided by Patrick Hofmann and
Robert Pincus of CU/NOAA.
Several options for treating solar variability are available based on the
NRLSSI2 solar source model, which allows the use of a fixed solar constant
(1360.85 Wm-2), a time-varying total solar irradiance based on the mean solar
cycle, or a varying total solar irradiance defined by specific time-varying
input indices for facular brightening and sunspot dimming. The constant total
solar irradiance (1368.22 Wm-2) based on the Kurucz model in all versions of
RRTMG_SW prior to v4.0 also remains available.