Estimated desert-dust ice nuclei profiles from polarization lidar: methodology and case studies

摘要

A lidar method is presented that permits the estimation of heightprofiles of ice nuclei concentrations (INC) in desert dust layers. Thepolarization lidar technique is applied to separate dust and non-dustbackscatter and extinction coefficients. The desert dust extinctioncoefficients σ_d are then converted to aerosol particle numberconcentrations APC₂₈₀ which consider particles with radius> 280 nm only. By using profiles of APC₂₈₀ and ambienttemperature T along the laser beam, the profile of INC can be estimatedwithin a factor of 3 by means of APC-T-INC parameterizations from theliterature. The observed close relationship between σ_d at 500 nmand APC₂₈₀ is of key importance for a successful INC retrieval. Westudied this link by means of AERONET (Aerosol Robotic Network) sun/skyphotometer observations at Morocco, Cabo Verde, Barbados, and Cyprus duringdesert dust outbreaks. The new INC retrieval method is applied to lidarobservations of dust layers with the spaceborne lidar CALIOP (Cloud AerosolLidar with Orthogonal Polarization) during two overpasses over the EARLINET(European Aerosol Research Lidar Network) lidar site of the Cyprus Universityof Technology (CUT), Limassol (34.7° N, 33° E), Cyprus. Thegood agreement between the CALIOP and CUT lidar retrievals of σ_d, APC₂₈₀, and INC profiles corroborates the potential of CALIOP toprovide 3-D global desert dust APC₂₈₀ and INC data sets.