Simultaneous vertical LIDAR profiling of Saharan dust layers and high-altitude cirrus clouds in the troposphere

Mineral dust and cirrus clouds are recognized to be among the major modulators of the atmospheric energy budget. Sahara Desert is the Earth’s largest source of mineral dust of natural origin. Saharan dust intrusions in the atmosphere over Europe are frequently accompanied by a parallel occurrence of cirrus clouds. Studies on the vertical aerosol distribution in such cases are important in providing a better understanding of the radiative effects of aerosols and clouds, and for the development of more accurate climate models. Lidars are considered as one of the leading techniques for conducting such studies, due to their high range/time resolution and sensitivity to optically-thin aerosol layers and clouds. In this work, we present results of lidar observations of the simultaneous presence of Saharan dust layers and cirrus clouds in the troposphere, with regard to their possible interaction, particularly in cases when the Saharan dust particles act as nuclei in cirrus cloud formation. Accordingly, experimental data derived from the regular long-term lidar investigations of Saharan dust loadings above Sofia, Bulgaria, are described and analyzed. The aerosol measurements were carried out by an elastic-backscatter lidar based on a frequency-doubled Nd:YAG laser. The experimental results are presented as color maps of the aerosol density distribution dynamics and by time-averaged vertical profiles of the aerosol backscatter coefficient. The process of cirrus cloud nucleation on desert dust particles is detected and analyzed in its development and evolution.