Edge effect correction formula for superspheroids using the Debye series.

Accurate quantification of the effects of nonspherical particles (e.g., ice crystals in cirrus clouds and dust aerosol particles) on the radiation budget in the atmosphere-earth coupled system requires a robust characterization of their light scattering and absorption properties. Recent studies have shown that it is feasible to compute the single-scattering properties of all sizes of arbitrary nonspherical atmospheric particles by combining the numerically exact invariant imbedding T-matrix (IITM) method and the approximate physical geometric optics method (PGOM). IITM cannot be implemented for very large-sized particles due to its tremendous demand on computational resources. While either method is usable for moderate sized particles, PGOM does not include the edge effect contributions to the extinction and absorption efficiencies. Unfortunately, we can only rigorously calculate the edge effect contributions to the extinction and absorption efficiencies for spheres and spheroids. This study develops empirical formulas for the edge effect contributions to the extinction and absorption efficiencies in the case of a special superspheroid called a superegg by modifying the formulas for the extinction and absorption efficiencies of a spheroid to account for the changes in roundness. We use the superegg edge effect correction formulas to compare the optical properties of supereggs and simple, convex particles, as an initial approximation to more complex atmospheric aerosols. This study is the first step towards quantifying the edge effect contributions to the extinction and absorption efficiencies of a wide range of natural nonspherical particles.