Aerosol Climatology at Pune, Western India: Implications to Direct Radiative Forcing and Heating Rates

Extensive aerosol observations were carried out at Indian Institute of Tropical Meteorology (IITM), Pune, an urban site in the western part of the country, using a Prede (Model POM-01L) sun/sky radiometer and a bi-static Argon ion lidar since December 2000 and October 1986, respectively. The sun/sky radiometer was operated daily at every 15 minute interval during day-time to derive column aerosol optical parameters such as aerosol optical depth (AOD), single scattering albedo (SSA), asymmetry parameter (ASY) while the lidar was operated weekly in the early-night period to derive vertical distributions of aerosol number density. The sun/sky radiance data collected during the above period have been analysed by using the radiative transfer model SkyRadPack version 3.0 (Nakajima et al. 1996) to retrieve AOD, SSA and ASY. AOD and SSA retrieved at 15-minutes interval were averaged to get monthly means. On every year from 2000 to 2005, monthly means of AOD show gradual increase of aerosol loading from December to April and Angstrom exponent decreases from March due to local as well as transported dust from African / Arabian regions through Arabian Sea. Monthly means of SSA show decrease from December to April and the wavelength dependence also indicate the abundance of dust from March to May. Lidar-derived vertical distributions yield minimum during the monsoon months, gradually builds up during the post-monsoon and winter months, and finally peaks during the pre-monsoon months in every year (Devara et al., 2002). The aerosol climatology of optical/radiative parameters and their vertical distribution are used for estimating aerosol radiative forcing (ARF) and atmospheric heating rates by using a discrete-ordinate radiative transfer model (Ricchiazzi et al., 1998, Pandithurai et al. 2004). Details of the experimental methods, data, results of aerosol climatology and implications to radiative forcing and associated heating rates will be presented. References Devara, P.C.S., R.S. Maheskumar, P.E. Raj, G. Pandithurai and K.K. Dani (2002), Recent trends in aerosol climatology and air pollution as inferred from multi-year lidar observations over a tropical urban station, Int. J. Climatol., 22, 435-449. Nakajima, T., G. Tonna, R. Rao et al. (1996), Use of sky brightness measurements from ground for remote sensing of particulate polydispersions, Appl. Opt., 35, 2672-2686. Pandithurai, G., R.T. Pinker, P.C.S. Devara and T. Takamura (2004), Aerosol radiative forcing over a tropical urban station in India, Geophys. Res. Lett., 31, L12107, doi: 10.1029/2004GL019702. Ricchiazzi, P., S. Yang, C. Gautier and D. Sowle (1998), SBDART, A research and teaching software tool for plane parallel radiative transfer in the Earth's atmosphere, Bull. Amer. Met. Soc., 79, 2101-2114.