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Absorbing aerosols supplements the global warming caused by greenhouse gases. However, unlike greenhouse gases, the effect of absorbing aerosol on climate is not known with certainty owing to paucity of data. Also, uncertainty exists in quantifying the contributing factors whether it is biomass or fossil fuel burning. Based on the observations of absorption coefficient at seven wavelengths and aerosol optical depth (AOD) at five wavelengths carried out at Gadanki (13.5° N, 79.2° E), a remote village in peninsular India, from April to November 2008, as part of the "Study of Atmospheric Forcing and Responses (SAFAR)" pilot campaign we discuss seasonal variation of black carbon (BC) concentration and aerosol optical depth. Also, using spectral information we estimate the fraction of fossil-fuel and non-fossil fuel contributions to absorption coefficient and contributions of soot (Black Carbon), non-soot fine mode aerosols and coarse mode aerosols to AOD. BC concentration is found to be around 1000 ng/m3 during monsoon months (JJAS) and around 4000 ng/m3 during pre and post monsoon months. Non-fossil fuel sources contribute nearly 20% to absorption coefficient at 880 nm, which increases to 40% during morning and evening hours. Average AOD is found to be 0.38±0.15, with high values in May and low in September. Soot contributes nearly 10% to the AOD. This information is further used to estimate the clear sky aerosol direct radiative forcing. Top of the atmosphere aerosol radiative forcing varies between −4 to 0 W m−2, except for April when the forcing is positive. Surface level radiative forcing is between −10 to −20 W m−2. The net radiation absorbed within the atmosphere is in the range of 9 to 25 W m−2, of which soot contributes about 80 to 90%.

Study of Atmospheric Forcing and Responses (SAFAR) is a five year (2009–2014) research programme specifically to address the responses of the earth's atmosphere to both natural and anthropogenic forcings using a host of collocated instruments operational at the National Atmospheric Research Laboratory, Gadanki (13.5° N, 79.2° E), India from a unified viewpoint of studying the vertical coupling between the forcings and responses from surface layer to the ionosphere. As a prelude to the main program a pilot campaign was conducted at Gadanki during May–November 2008 using collocated observations from the MST radar, Rayleigh lidar, GPS balloonsonde, and instruments measuring aerosol, radiation and precipitation, and supporting satellite data. We show the importance of the large radiative heating caused by absorption of solar radiation by soot particles in the lower atmosphere, the observed high vertical winds in the convective updrafts extending up to tropopause, and the difficulty in simulating the same with existing models, the upward traveling waves in the middle atmosphere coupling the lower atmosphere with the upper atmosphere, their manifestation in the mesospheric temperature structure and inversion layers, the mesopause height extending up to 100 km, and the electro-dynamical coupling between mesosphere and the ionosphere which causes irregularities in the ionospheric F-region. The purpose of this communication is not only to share the knowledge that we gained from the SAFAR pilot campaign, but also to inform the international atmospheric science community about the SAFAR program as well as to extend our invitation to join in our journey.