Extension of T-matrix to scattering of electromagnetic plane waves by non-axisymmetric dielectric particles: application to hexagonal ice cylinders

The calculation of scattering by cirrus particles at intermediate size para meters greater than 20 has not as yet been satisfactorily solved with exact theory. This has made it difficult to represent scattering and absorption of ice clouds in remote sensing retrievals and in modelling radiative forci ng. The T-matrix approach applied to ice particles has previously been impl emented only for axisymmetric particles, but ice clouds consist of particle s which are not axisymmetric. In this paper an implementation of T-matrix w hich provides exact solutions for scattering and absorption from non-axisym metric particles is presented. Rigorous tests demonstrate the stability and accuracy of the method. Results for finite hexagonal cylinders are present ed. The general T-matrix formulation has major conceptual and practical adv antages over other existing methods such as the finite difference time doma in (FDTD) and the discrete dipole approximation (DDA). These advantages are due largely to its analytic character, which allows exact fulfillment of t he radiation condition. Other advantages are the restriction of calculation s to the scatterer's surface, and the exploitation of particle symmetries w hich considerably simplifies computation. The new T-matrix implementation i s tested against existing T-matrix results for the circular cylinder and th e cube in terms of differential scattering cross-sections, no differences a re found between the T-matrix calculations. Comparisons with a recently imp roved implementation of FDTD for randomly oriented hexagonal ice columns sh ow good agreement with T-matrix in terms of absorption and extinction effic iencies. Crown Copyright (C) 2001 Published by Elsevier Science Ltd. All ri ghts reserved.