Saharan dust intrusions in the Mediterranean area: Three years of Raman lidar measurements

[ 1] A multiyear climatological study of Saharan dust intrusions in the central Mediterranean in terms of aerosol optical parameters vertical profiles is carried out for the first time. Observations are performed at Istituto di Metodologie per l'Analisi Ambientale (IMAA) Raman/elastic lidar station located in Tito Scalo, Potenza (40 degrees 36'N, 15 degrees 44'E), from May 2000 to April 2003, in the framework of European Aerosol Research Lidar Network (EARLINET). Desert dust aerosols are observed between 1.8 and 9 km in 112 days. Mean values within the desert dust layer of 76 Mm(-1), 1.0 Mm(-1) sr(-1) and 0.54 Mm(-1) sr(-1) are observed for aerosol extinction at 355 nm and aerosol backscatter at 355 and 532 nm. Desert dust layer optical depth at 355 nm ranges between 0.001 and 0.68, with a mean of 0.13. The source origin is the central Sahara in about 65% of the cases, the western Sahara in about 31%, and only in four cases the eastern Sahara. The most extended database of Saharan dust lidar ratio data was collected: Values range between 6 and 126 sr following a 3-modal Gaussian distribution centered at 22, 37 and 57 sr. A mean value of 37 sr is found around the center of the Saharan dust layer. At its extremes, where dust particles are mixed to PBL and free troposphere background aerosols, a mean value of 57 sr is found. Finally, low lidar ratio values of about 22 sr are observed when large amount of dust is transported at low altitudes over the Mediterranean Sea.