Dual-wavelength Raman lidar observations of the extinction-to-backscatter ratio of Saharan dust

Abstract

For the first time, height profiles of the extinction-to-backscatter ratio (lidar ratio) of desert dust particles were simultaneously measured at 355 and 532 nm. The observations were performed with an advanced Raman lidar during two longrange Saharan dust outbreaks at Leipzig, Germany (51.3°N, 12.4°E), in August and October 2001. Measured desert-dust lidar ratios are needed for a proper profiling of the climate-relevant volume extinction coefficient of the dust particles with widely used standard backscatter lidars. Unexpectedly large lidar ratios, mainly between 50 and 80 sr, were found in the Saharan dust plumes. The lidar ratios at 355 nm were, on average, higher by 10%-30% than the ones at 532 nm, probably due to enhanced light absorption in the UV. The large lidar ratios can be explained by model calculations, available in the literature for 532 nm, which focus on the deviations between the scattering characteristics of spheres and spheroids.