Analysis of Desert Dust Outbreaks Over Southern Europe Using CALIOP Data and Ground-Based Measurements

摘要

Saharan dust outbreaks are one of the major aerosol sources in Southern Europe. Dust affects the radiative balance of the Earth-atmosphere system and impacts health. The assessment of Saharan outbreaks requires information about the vertical distribution of dust in the atmosphere, usually obtained from lidar measurements, such as the ones performed by the spaceborne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) sensor. In this paper, we have used CALIOP level-1 daytime data in combination with aerosol optical depth (AOD) measurements from Aerosol Robotic Network (AERONET) ground-based photometers to obtain aerosol profiles during 23 dust outbreaks over Southern Europe. These profiles are used for two main purposes: analyzing the lidar ratio values and vertical distribution of dust and evaluating the performance of version 3 of CALIOP algorithms. The mean lidar ratio obtained from the synergic method ranged between 47.7 and 49.0 sr, depending on the criterion used to average CALIOP signal. The dust layers traveled at a wide range of altitudes, from surface level up to 7.6 km. We found that the AOD values retrieved from CALIOP level 2 (version 3) and AERONET were not correlated (r <; 0.2). In addition, we observed that the mean AOD obtained by satellite retrievals, between 0.16 and 0.18, was lower than the mean AERONET value, i.e., 0.33, by 50%. These differences in the AOD were found to be caused by two main reasons: misclassification of dense dust layers as clouds by CALIOP algorithms, mainly over 4 km, and limitations of CALIOP algorithms to detect weak aerosol layers, particularly between 1.5 and 2.5 km.