Validation of RRTM_LW relative to LBLRTM
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_LW 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 climate research facilities
- water vapor continuum absorption coefficients are consistent with those in MT_CKD 2.5.
fluxes and cooling rates can be calculated over sixteen bands contiguous
bands in the longwave (10-3250 cm-1)
- scattering capability is available through the radiative transfer solver DISORT
modeled molecular absorbers are: water vapor, carbon dioxide, ozone,
nitrous oxide, methane, oxygen, nitrogen and halocarbons.
fluxes calculated by RRTM agree with those computed by LBLRTM within 1.5
W/m2 at all levels, and the computed cooling rates agree to within 0.1
K/day in the troposphere and 0.3 K/day in the stratosphere (see above plot).
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 ice particle parameterization from Fu, Yang, and Sun (J. Climate,
Vol 11, 1998, pp. 2223 - 2237) or from the ice particle parameterization available from the STREAMER model v3.0.
Atmospheric and Environmental Research