RAMAN LIDAR OBSERVATIONS OF A SAHARAN DUSTOUTBREAK EVENT: CHARACTERIZATION OF THE DUSTOPTICAL PROPERTIES AND DETERMINATION OF PARTICLESIZE AND MICROPHYSICAL PARAMETERS

The Raman lidar system BASIL was operational in Achern (Black Forest) between 25 May and 30 August 2007 in the frame of the Convective and Orographically- induced Precipitation Study (COPS). The system performed continuous measurements over a period of approx. 36 hours 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. Data clearly reveals the presence of the dust cloud between 18:00 and 03:00 UTC, with the presence of two almost separate aerosol layers: a lower layer located between 1.5 and 3.5 km and an upper layer extending between 3.0 and 6.0 km. An inversion algorithm was used to retrieve particle microphysical parameters, i.e., mean and effective radius, number, surface area, and volume concentration, complex refractive index, as well as the parameters of a bimodal particle size distribution, 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 spheroidal particles. 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 dominance in the upper dust layer of a coarse mode with radii 3-6 μm. Effective radius, number density and volume concentration vary with altitude in the range 0.1-1.4 μm, 200-1500 cm-3 and 6- 80 μm3/cm3, respectively, while real and imaginary part of the complex refractive index are in the range 1.45-1.62 and 0.005-0.012, respectively.