Measurements of Saharan dust aerosols over the Eastern Mediterranean using elastic backscatter-Raman lidar, spectrophotometric and satellite observations in the frame of the EARLINET project

摘要

We report on the vertical distributions of Saharan dust aerosols over theN.E. Mediterranean region, which were obtained during a typical dustoutbreak on August 2000, by two lidar systems located in Athens andThessaloniki, Greece, in the frame of the European EARLINET project. MODISand ground sun spectrophotometric data, as well as air-mass backwardtrajectories confirmed the existence of Saharan dust in the case examined,which was also successfully forecasted by the DREAM dust model. The lidardata analysis for the period 2000-2002 made possible, for the first time, anestimation of the vertical extent of free tropospheric dust layers [meanvalues of the aerosol backscatter and extinction coefficients and theextinction-to-backscatter ratio (lidar ratio, LR) at 355 nm], as well as aseasonal distribution of Saharan dust outbreaks over Greece, undercloud-free conditions. A mean value of the lidar ratio at 355 nm wasobtained over Athens (53±1 sr) and over Thessaloniki (44±2 sr)during the Saharan dust outbreaks. The corresponding aerosol opticalthickness (AOT) at 355 nm, in the altitude range 0-5 km, was 0.69±0.12and 0.65±0.10 for Athens and Thessaloniki, respectively (within thedust layer the AOT was 0.23 and 0.21, respectively). Air-massback-trajectory analysis performed in the period 2000-2002 for all Saharandust outbreaks over the N.E. Mediterranean indicated the main pathwaysfollowed by the dust aerosols.