SHDOM Optical Property Generation Overview

The optical property file generation system for SHDOM has been upgraded to be more flexible and accurate. Instead of the cloudprp program, there are now three Fortran 90 programs: make_mie_table.f90 and make_ice_table.f90 for making scattering tables and propgen.f90 for generating the property file from a particle properties file. The particle properties file specifies the mass content (g/m^3) and effective radius (microns) of each particle component at each grid point. The make_mie_table program generates scattering tables for gamma or lognormal size distributions of spherical particles, while make_ice_table generates scattering tables in the shortwave for gamma distributions of one of eight ice crystal shapes using Ping Yang's single scattering properties. The program plotscattab.f90 makes a plotting file of phase functions versus angle from the Legendre series in a scattering table file. The propgen program allows an arbitrary mixture of any number of pure components at each grid point. The extinction and single scattering albedo from all the components are combined exactly, while phase functions existing in the scattering tables and newly created phase functions are chosen so that the phase function error is smaller than user specified tolerances. The result is a tabulated phase function format property file for SHDOM with a small as possible memory requirement that closely approximates the desired optical property distribution.

The example Unix script run_propgen_example shows how to make scattering tables and run propgen to generate a property file for SHDOM. Scattering tables are made at two wavelengths for lognormal distributions of spherical dust aerosols, gamma distributions of cloud water droplets, and gamma distributions of plate and rough aggregate ice crystals. The example particle file nauru19990707.part specifies the mass content and effective radius distributions for a horizontally uniform aerosol layer (particle type 1) from the surface to 1.4 km, a broken cumulus water cloud layer (type 2) from 0.59 to 2.03 km, and a cirrus layer made of plates and aggregates (types 3 and 4) from 8.75 to 14.75 km. The two-dimensional (X-Z) cumulus and cirrus cloud distributions are derived from the ARM millimeter-wave cloud radar on Nauru Island. The distribution includes an IDL program plot_propgen_example.pro which plots the components of the particle file, the resulting extinction and single scattering fields, and radiance output from SHDOM (requires other IDL files in the SHDOM distribution).