Modeling Single Scattering and Radiative Properties of Cirrus Clouds
Final rept. 23 Sep-30 Sep 98
STATE UNIV OF NEW YORK AT STONY BROOK
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The specific objective of this research has been the development and improvement of theoretical models to simulate the effect of nonsphericity on single scattering 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 T-matrix computations for nonabsorbing and weakly absorbing nonspherical particles. Second, we use exact T-matrix computations and the Kirchhoff approximation to show that the delta function 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. Third, we have used the improved T-matrix method to compute the linear depolarization ration for polydispersions of randomly oriented ice spheroids, circular cylinders, and Chebyshev particles with sizes typical of young contrails. We have shown that ice crystals with effective radii as small as several tenths of a micron can already produce 3 exceeding 0.5 at visible wavelengths.