Optical characteristics of aerosols as inferred from a high spectral resolution radiometric observations over Pune during the INDOEX IFP-99

A high spectral resolution radiometer was operated at the Indian Institute of Tropical Meteorology, Pune during the period of Indian Ocean Experiment-Intensive Field Phase (INDOEX-IFP) from 1 January to 31 March 1999, The observations were carried out for about 45 days, of which about 29 days' data collected during the clear-sky conditions were used for the study reported here, The experiment was conducted from post-sunrise to pre-sunset periods in a day. Observations were carried out at an interval of 10 min during the period of rapid solar zenith angle variation and at every 30 min during the intervening period, From the aerosol extinction data thus collected the aerosol optical depths and corresponding size distributions were computed using the constrained linear inversion method far each experimental day, The optical depth computations were also carried out for fullday, forenoon and afternoon periods. Monthly mean optical depths were obtained from the average of individual day's optical depth. Aerosol optical depths and the corresponding size distributions were calculated at every 0.025 mum interval, The aerosol optical depths varied between 0.17 and 0.52 during the IFP, The forenoon optical depths were found to be higher than those obtained for the afternoon period. Also, the optical depth range was more during the IFP when compared to the same during the first field phase. The retrieved size distributions showed monomodal throughout the IFP, bimodal during January and March, and power-law type during February. The Junge size exponent v, which is an indicator of size distribution of aerosols, varied between 2.0 and 2.2. The daily variation of aerosol optical depth at 0.55 mum showed an increasing trend during the study period.