Date: February 2009
Modified the value of the single scattering albedo threshold (from 0.9995
to 0.9999995) that selects between the general 2-stream scattering solution
(for most SSA values) and a simpler, conservative scattering solution when
SSA is close to 1.0. The new more restrictive threshold generates improved
results within multi-layer, highly scattering clouds when the SSA is just
under one. This change will affect fluxes and will significantly affect
heating rates within highly scattering clouds, especially those that extend
over multiple layers. Negligible changes also occur in clear sky since the
single scattering albedo can be close to this threshold when Rayleigh
scattering dominates the shortwave extinction. Use of this modification is
Added several code changes to the two-stream solver that prevent potential
exception problems under single precision.
A new flag was installed (idelm) that is used to select between either
unscaled 'true' direct and diffuse fluxes (idelm=0) or delta-scaled direct
and diffuse fluxes (idelm=1). This flag is read from the input file in the
column version of the model. In the code to be used in GCMs, it is set by
default to 1 to provide scaled direct and diffuse fluxes. Total fluxes
continue to be provided only as delta-scaled quantities.
Added a new makefile to the build directory for IBM XL platforms.
Updated the rrtmg_sw_instructions.txt file in the doc directory.