Modelling light scattering by mineral dust using spheroids: assessment of applicability
1Climate Change, Finnish Meteorological Institute, P.O. Box 503, 00101 Finland
2Department of Physics, University of Helsinki, P.O. Box 48, 00014 Finland
3Swedish Meteorological and Hydrological Institute, Folkborgsvägen 1, 601 76 Norrköping, Sweden
Abstract. We study the applicability of spheroidal model particles for simulating the single-scattering optical properties of mineral dust aerosols. To assess the range of validity of this model, calculations are compared to laboratory observations for five different dust samples at two wavelengths. We further investigate whether the best-fit shape distributions of spheroids for different mineral dust samples have any similarities that would allow us to suggest a generic first-guess shape distribution for suspended mineral dust. We find that best-fit shape distributions vary considerably between samples and even between wavelengths, making definitive suggestions for a shape distribution difficult. The best-fit shape distribution also depends strongly on the refractive index assumed and the cost function adopted. However, a power-law shape distribution which favours those spheroids that depart most from the spherical shape is found to work well in most cases. To reproduce observed asymmetry parameters, best results are obtained with a power-law shape distribution with an exponent around three.