One-year observations of the vertical structure of Saharan dust over Athens, Greece monitored by NTUA's lidar system in the frame of EARLINET

摘要

Suspended aerosol particles play a significant role in the Global Change issue. Every year huge quantities of Saharan dust are transported to the European continent and North Atlantic Sea. Since May 1, 2000, an elastic backscatter lidar station is in operation in Athens, Greece, in the frame of the European LIDAR Network (EARLINET), aiming at the monitoring of extreme aerosol events over the Eastern Mediterranean Sea. During the first year of operation 20 cases of Saharan dust transport to the East Mediterranean Sea (EMS), were successfully observed. The lidar data are correlated with meteorological and satellite observations, including the aerosol index (AI) data from the Total Ozone Mapping Spectrometer (TOMS) and the SeaWiFS satellite images. The analysis of the data collected so far, made possible a first statistical approach of the vertical and horizontal extent and of the seasonal variation of free tropospheric Saharan dust layers over the EMS area. The main results of this work are: i) multiple dust layers of variable thickness (0.5-4 km) are systematically observed in the altitude region 2-6 km, ii) Saharan dust outbreaks take place all year round, with more pronounced frequencies during the summer period and can persist for a few days (1-5), iii) 24-48 hours are usually needed for the Saharan air masses to reach the EMS area, and finally iv) the TOMS AI values can reach 1.5-3.5 over Greece. These lidar data gave the aerosol vertical structure over the Eastern Mediterranean Sea during Saharan dust outbreaks and can be a direct input for global radiative transfer models.