LIDAR-OBSERVED LONG-TERM VARIATIONS IN URBAN AEROSOL CHARACTERISTICS AND THEIR CONNECTION WITH METEOROLOGICAL PARAMETERS

More than 200, weekly spaced, lidar-derived vertical profiles of aerosol concentration in the lower atmosphere (up to 1380 m above ground level) obtained during night-time between October 1986 and August 1990 at the Indian Institute of Tropical Meteorology (IITM), Pune (18-degrees-32'N, 73-degrees-51'E, 559 m above mean sea-level), India, have been used to study the long-term variations in aerosol concentration in different air layers. Selected meteorological parameters for the above period at Pune have also been examined to investigate their association with the aerosol concentration. The spectral analysis of the data revealed significant periodicities in four different characteristic ranges, namely 2.5-13.5, ca. 27, ca. 33 and 40-48 weeks in both lidar-derived aerosol content and meteorological parameters; the fourth range being more predominant in all the parameters. These results, together with those of cross-correlation analysis of the data, indicate an association between the long-term trends present in both aerosol and meteorological parameters at the station.