RRTM is a rapid radiative transfer model which utilizes the correlated-k
approach to calculate fluxes and heating rates efficiently and accurately.
Key features of RRTM_SW are:
k-distributions are obtained directly from a line-by-line radiative transfer
code, LBLRTM , which has been extensively
validated against observations, principally at the ARM SGP site
fluxes and cooling rates are calculated over fourteen contiguous
bands in the shortwave (820-50000 cm-1)
modeled sources of extinction are water vapor, carbon dioxide, ozone, methane,
oxygen, aerosols, and Rayleigh scattering
DISORT is used to perform scattering calculations
agreement with line-by-line calculations: 1 W/m2 for direct
irradiance, 2 W/m2 for diffuse irradiance
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.
Atmospheric and Environmental Research