Variability in size of raindrops
The Mie algorithm assumes scattering from a single sphere, but a rainbow involves scattering from millions of raindrops. In practice, raindrops are not of uniform size. MiePlot simulates the effect of size dispersion by performing N calculations for sizes described by Normal or Log-Normal statistical distributions. Fig. 1 below shows that even very small variations in the size of the drops (e.g. a standard deviation of 0.1%) can have a considerable effect.
Fig. 1 Intensity v. scattering angle for red light (λ = 0.65 µm) by a spherical water drop of nominal radius r = 100 µm for perpendicular polarisation
