Spectral behavior of optical coefficients and microphysical characteristics of aerosol particles

Abstract

The paper considers the regularities of the spectral variations in the extinction and backscattering coefficients and in a lidar ratio, on the one hand, and the microphysical characteristics of aerosol particles, described by a complex refractive index and particle size distribution function, on the other hand. Based on the Mie calculations for mono- and bimodal distributions, it is shown that the Angstrom parameters for the extinction coefficient are informative with respect to the contribution of small particles to the volume concentration V f /V t and weakly depend on the geometric mean radius of small particles R f . On the contrary, the Angstrom parameters for the backscattering coefficient are informative with respect to R f and are almost independent of V f /V t . The lidar ratio and Angstrom parameters for the backscattering coefficient depend strongly on the real m R and imaginary m I parts of the refractive index. Restricting the variability range of lidar ratio limits the variability range of m I (for a fixed m R ), which shifts toward larger m I values with an increase in m R . The lidar ratio may increase with growth of the wavelength only for large particles when V f /V t < 0.2 and the real part of the refractive index is ∼1.40.