Lidar profiling of aerosols and clouds for regional climate and pollution research

Abstract

The space-time variability of aerosol inhomogeneities provides unique information on atmospheric behavior needed for climate and environmental research and operational programs. An additional indirect forcing from aerosols results from their involvement in nucleation and growth of cloud droplets, reducing droplet size and thereby potentially influencing cloud albedo. These studies have particular significance over tropics where the convective and dynamical processes associated with high-altitude thunderstorms greatly affect the vertical distributions of aerosols and pre-cursor gases. As the anthropogenic share of the total aerosol loading is quite substantial over many parts of the world, it is essential to monitor the aerosol features systematically over longer time scales. Such observations are very important for understanding the coupling processes that exist between physico-chemical, radiative, dynamical and biological phenomena in the Earth's environment, and provide valuable input information for modeling and simulation studies of climate and air quality. The multi-year aerosol number density data acquired during October 1986-September 2000 with a computer-controlled lidar at the Indian Institute of Tropical Meteorology (IITM), Pune, an urban station in India have been utilized to investigate (i) climate variability, (ii) cloud macro-physical parameters and (iii) environmental pollution. The results reveal a long-term trend in aerosol loading, single and multiple layer clouds with low cloud-base during the south-west monsoon months, and high pollution potential during winter late evenings. The trends in aerosol loading and air quality are found to be changing from year to year depending upon meteorological parameters (precipitation in particular). Some of these parameters have also been compared with co-located complementary facilities such as solar radiometers. In order to enlarge the scope of these studies, a dual polarization micro pulse lidar (DPMPL) has been installed at IITM recently to investigate the cloud composition, and aerosol-cloud-climate interactions. The initial results obtained from this state-of-the-art lidar system showed interesting features in the time evolution of nocturnal (stable) boundary layer which have strong bearing on air pollution potential over the experimental station. The complete details of the lidar systems used in the above studies together with discussion of salient results are presented in this paper.