
Accession Number : ADA329812
Title : Modeling Single Scattering and Radiative Properties of Cirrus Clouds
Descriptive Note : Annual rept. 23 Sep 9630 Sep 97
Corporate Author : STATE UNIV OF NEW YORK AT STONY BROOK MARINE SCIENCES RESEARCH CENTER
Personal Author(s) : Mishchenko, Michael I.
PDF Url : ADA329812
Report Date : 15 SEP 1997
Pagination or Media Count : 13
Abstract : The specific objective of this research is the development and improvement of theoretical models to simulate the effect of nonsphericity on singlescattering properties of cirrus cloud particles in the visible and infrared spectral regions. First, we have shown that using a matrix inversion scheme based on a special LU factorization rather than on the standard Gaussian elimination significantly improves the numerical stability of Tmatrix computations for nonabsorbing and weakly absorbing nonspherical particles. As a result, the maximum convergent size parameter for particles with small or zero absorption can increase by a factor of several and can exceed 100. Comparisons of Tmatrix and geometric optics (GO) computations for large, randomly oriented spheroids and finite circular cylinders show that the range of applicability of the ray tracing approximation depends on the imaginary part of the refractive index and is different for different elements of the scattering matrix. Second, we use exact Tmatrix computations and physical considerations based on the Kirchhoff approximation to show that the deltafunction transmission peak predicted by the GO approximation for hexagonal ice crystals is an artifact of GO completely ignoring physical optics effects and must be convolved with the Fraunhofer pattern, thereby producing a phase function component with an angular profile similar to the standard diffraction component. We have performed this convolution with a simple procedure which supplements the standard ray tracing code and makes the computation of the phase function and its Legendre expansion both more physically realistic and more accurate.
Descriptors : *CIRRUS CLOUDS, MATHEMATICAL MODELS, COMPUTERIZED SIMULATION, LIGHT SCATTERING, REFRACTIVE INDEX, ICE, DIFFRACTION, VISIBLE SPECTRA, RAY TRACING, INFRARED SPECTRA, LEGENDRE FUNCTIONS.
Subject Categories : Meteorology
Numerical Mathematics
Distribution Statement : APPROVED FOR PUBLIC RELEASE