Saharan desert dust microphysical properties from principle component analysis (PCA) inversion of raman lidar data over western Europe

A large Saharan desert dust outbreak in May 2009 was
detected using a Raman lidar, deployed in Leipzig, Germany. The optical data showed three distinct vertical layers, two with little spectral variation in the extinction, and one with a large spectral variation in both the scattering ratio and extinction measurements. Furthermore, the layer with the large spectral variation showed much larger particle depolarisation ratios and lidar ratios than the two other layers, which is typical for Saharan desert dust. Backtrajectory and dust distribution forecast and hindcast models showed that the different layers all originated over the Sahara, but had different transport histories. The measurements were inverted to derive microphysical properties of the particles in the layers. The method derives integral properties of the aerosols using principle component analysis, adapted for use in the troposphere. It accounts for varying refractive indices of the ambient aerosols, as shown in this paper.