Vertical and spatial distribution of elevated aerosol layers obtained using long-term ground-based and space-borne lidar observations

摘要

In this study, long-term ground-based and space-borne lidar measurements are used to understand the vertical (surface to 30 km) and spatial distribution of aerosols. First, the vertical distribution of aerosol extinction (AE) covering from near surface to 30 km is provided by combining Micro Pulse Lidar and Mie lidar observations colocated over a tropical station Gadanki (13.5 degrees N, 79.2 degrees E), India. The presence of two elevated aerosol layers, one between 2 and 5 km (lower troposphere) and the other between 15 and 18 km (Upper Troposphere and Lower Stratosphere (UTLS)), are simultaneously observed during the Indian summer monsoon season. Second, the spatial extent of these elevated aerosol layers obtained using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) measurements reveals the presence of the lower layer extending from Africa to South Asia during both pre-monsoon and monsoon seasons. However, the UTLS layer is confined from middleeast to the China Sea only during monsoon season, also known as Asian Tropopause Aerosol Layer (ATAL). Third, aerosol sub-types obtained for these elevated aerosol layers using CALIPSO measurements reveals the dominance of polluted dust (44.6%) whereas the occurrence frequency of polluted continental, dust and elevated smoke is similar to 19.6%, 20.7% and 13.1%, respectively, for the lower layer. However, the frequency of volcanic ash and sulfate aerosols is similar to 50.3% and 49.7%, respectively, for the UTLS layer. Depolarization ratio (color ratio) values varies between 0.21 and 0.34 ( 0.6) in the lower layer while the values 0.15 (0.6) are present in the UTLS layer during monsoon season revealing the influence of non-spherical and coarse mode particles in the lower layer while spherical and fine mode particles in the UTLS region over the site. This information is very much useful in estimating reliable radiative forcing due to these elevated aerosol layers on the background atmosphere involved in assessing their impact on the regional climate.