The Raman lidar system BASIL was operational in Achern (Black Forest) between 25 May and 30 August 2007 in the framework of the Convective and Orographically-induced Precipitation Study (COPS). The system performed continuous measurements over a period of approx. 36h from 06:22 UTC on 1 August to 18:28 UTC on 2 August 2007, capturing the signature of a severe Saharan dust outbreak episode. The data clearly reveal the presence of two almost separate aerosol layers: a lower layer located between 1.5 and 3.5km above ground level (a.g.l.) and an upper layer extending between 3.0 and 6.0km a.g.l. The time evolution of the dust cloud is illustrated and discussed in the paper in terms of several optical parameters (particle backscatter ratio at 532 and 1064nm, the colour ratio and the backscatter Angström parameter).An inversion algorithm was used to retrieve particle size and microphysical parameters, i.e., mean and effective radius, number, surface area, volume concentration, and complex refractive index, as well as the parameters of a bimodal particle size distribution (PSD), from the multi-wavelength lidar data of particle backscattering, extinction and depolarization. The retrieval scheme employs Tikhonov's inversion with regularization and makes use of kernel functions for randomly oriented spheroids. Size and microphysical parameters of dust particles are estimated as a function of altitude at different times during the dust outbreak event. Retrieval results reveal the presence of a fine mode with radii of 0.1-0.2μm and a coarse mode with radii of 3-5μm both in the lower and upper dust layers, and the dominance in the upper dust layer of a coarse mode with radii of 4-5μm. Effective radius varies with altitude in the range 0.1-1.5μm, while volume concentration is found to not exceed 92μm 3cm -3. The real and imaginary part of the complex refractive index vary in the range 1.4-1.6 and 0.004-0.008, respectively. © 2012 Elsevier Ltd.

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