Aerosol Absorption and Radiative Forcing Estimations using Sun Photometry and Ground- Based Broadband Radiometry at Kanpur, India During the 2008 TIGERZ Campaign

The TIGERZ campaign was conducted in May and June of 2008 in northern India to investigate the unique combination of aerosols (dust, smoke, industrial pollution) found in the Indo-Gangetic region. Six permanent sunphotometer sites were established in Northern India with four sites positioned along the approximate ground track of the CALIPSO sensor that passed near Kanpur to acquire high frequency aerosol optical depth data and make sky radiance measurements that were processed to determine aerosol properties such as size distribution and absorption at four wavelengths. During days with a CALIPSO overpass by Kanpur (as well as for the closest tracks to the East and West), an additional three Cimel sunphotometers were positioned within 100m of the satellite track. Such collocated measurements allow for joint inversions using both ground based sky radiance measurements from Cimels and radiance measurements from CALIPSO. Preliminary results from the investigation will be shared including calculations of single scattering albedo (SSA) trends determined from Cimel sunphotometer and pyranometer measurements, lidar ratio statistics (calculated from the sunphotometer radiances) compared with the lookup values used by CALIPSO for this region and modeled aerosol forcing for the region. The Cimel sunphotometer routinely provides single scattering albedo as a calculated aerosol product, however these values are typically limited values acquired during almucantars from low sun conditions (solar zenith greater than 45 degrees) when sensitivity to aerosol absorption is maximized. With a fully characterized aerosol and a suitable radiative model, it's possible to estimate the SSA using a well-calibrated radiometer. During TIGERZ, we installed a Kipp and Zonen pyranometers that took flux measurements at 2-minute intervals alongside the Kanpur sunphotometer. In principle, the advantage of using the pyranometer in this scenario is that we are able to evaluate SSA for high sun angles when aerosol absorption information is unavailable from the sunphotometer. One month (May 2008) of single scattering albedos derived from irradiance measurements are presented and compared with the equivalent parameter determined from the standard Cimel almucantar protocol.