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The scattering of visible light by clouds is calculated from an efficient Monte Carlo code which follows the multiply scattered path of the photon. The single scattering phase function is obtained from the Mie theory by integration over a particle size distribution. The photons are followed through a sufficient number of collisions and reflections from the lower surface (which may have any desired albedo) until they make a negligible contribution to the intensity. Various variance reduction techniques were used to improve the statistics. The reflected and transmitted intensity is studied as a function of solar zenith angle, optical thickness, and surface albedo. The downward flux, cloud albedo, and mean optical path of the transmitted and reflected photons are given as a function of these same parameters. The numerous small angle scatterings of the photon in the direction of the incident beam are followed accurately and produce a greater penetration into the cloud than is obtained with a more isotropic and less realistic phase function. (Author).
The Monte Carlo codes LITE-I and LITE-II were used to compute light transmission data for point and plane sources. The results of these calculations showed that there is no correlation between the scattered transmission data for point isotropic and plane parallel sources. The LITE codes were used to analyze experimental data on light transport in the atmosphere. Reasonably good agreement was obtained for those cases where data were available to adequately describe the atmosphere at the time of the experiments. Calculations were performed to determine the angular dependence of the number albedo from thick cumulus clouds for 0.45 light incident at various angles to the cloud. The polar angular distributions of the reflected photons were found to be cosine distributions and the total number albedo was expressed mathematically. Studies were performed to determine the sensitivity of the LITE-I calculated scattered intensities for a point isotropic monochromatic source to changes in the source and receiver altitudes, aerosol number density, aerosol phase function, altitude variation of the aerosol scattering coefficient and the altitude of the bottom of a cloud layer above the source point. It was found for the source-receiver geometry considered in these studies that the LITE calculations were more sensitive to changes in the number density of the aerosol particles than to changes in the shape of the aerosol phase function. (Author).
The FLARE Monte Carlo procedure, which computes the transport of monochromatic light emitted by either point or plane-parallel sources in a plane atmosphere, was made operational. The FLARE procedure treats problems involving light transport in atmospheres where the scattering and absorption processes vary with altitude. The FLARE procedure was used to compute the scattered and direct intensities as a function of direction and horizontal range at receiver altitudes of 0, 1, 2, 5, and 10 km. Problems were run for 550 nm wavelength point isotropic sources at 1, 2, 5, 20 and 80 km altitude in a model atmosphere with a ground level meteorological range of 10 km. Calculations were made for the 550 nm wavelength point isotropic source at 2 km altitude in model atmospheres with ground level meteorological ranges of 3, 10, 25, and 50 km. Additional calculations were also performed for 450, 550, and 650 nm wavelength point isotropic sources at 2 km altitude in the model atmosphere with a 10 km ground level meteorological range. (Author).
Developments in three-dimensional cloud radiation over the past few decades are assessed and distilled into this contributed volume. Chapters are authored by subject-matter experts who address a broad audience of graduate students, researchers, and anyone interested in cloud-radiation processes in the solar and infrared spectral regions. After two introductory chapters and a section on the fundamental physics and computational techniques, the volume extensively treats two main application areas: the impact of clouds on the Earth's radiation budget, which is an essential aspect of climate modeling; and remote observation of clouds, especially with the advanced sensors on current and future satellite missions.