Saharan aerosol sensed over Warsaw by backscatter depolarization lidar

The estimates of the optical properties of mineral dust aerosol observed on April 13th and 14th, 2005 during SAWA (Saharan aerosol over Warsaw) experiment are described. Lidar signals at 532 and 1064 nm wavelengths were inverted with a modified Klett-Fernald algorithm. Aerosol optical depth measured with a sun-photometer allowed to reduce uncertainties in the inversion procedure. Further improvement of the estimation came from distinguishing three aerosol layers in the atmosphere on the basis of vertical profiles of optical properties. Having calculated vertical distributions of aerosol extinction coefficients, profiles of local Angstrom exponent were estimated. Independent information on depolarisation of 532 nm lidar returns, together with the assumption about the spheroidal shape and random orientation of aerosol particles, allowed to estimate the aspect ratio and size of particles on the basis of numerical calculations with transition matrix (T-matrix) algorithm by M. Mishchenko. Results indicate the mode radii of spheroids in the range of 0.15-0.3 mu m, and their aspect ratio in the range of 0.6-0.8 or 1.3-2.2 (two solutions are allowed). Small size of the particles is explained by dust deposition and mixing with boundary layer aerosol in the Mediterranean region.