Inter-Annual Variability of Radiative Forcing over the Northern Plains of Indian Sub- Continent using AERONET Sun-photometer, MODIS Terra, Aqua and CERES

Recent short term studies over the northern plains of the Indian sub-continent show very high aerosol optical depth (AOD) and high degree of seasonal and inter-annual variability of aerosols. Availability of relatively long term daily data (2001-2007), collocated over the same spatial (10km grid) and temporal (±30min) dimensions, from the ground (AERONET sun-photometer, level 2) and space platform (MODIS Terra and Aqua, level 2) provide a unique opportunity to study seasonal dependency and bias in satellite data for both late morning (Terra) and early afternoon (Aqua). Seasonal variability of AOD, COD (cloud optical depth) and validation of AOD (2001-2007) has been studied over the city of Kanpur, located centrally in the northern plains of the Indian sub-continent. We show quantitative seasonal and monthly dependency of bias, root mean square error and correlation coefficients. The observed aerosol optical parameters (AOD and Angström coefficient) and aerosol characteristics (fine mode fraction, effective radius and soot mass) vary with season (summer, winter and monsoon period). The seasonal and monthly variability of the associated aerosol radiative effect (ARE) based on AERONET sun-/sky-photometer and cloud radiative effect (CRE) from CERES for shortwave, and longwave at the surface, top-of-the-atmosphere (TOA) and net atmospheric for the period 2001-2007 will be presented in view of the observed dust events during summer, fog conditions during winter and poor or good monsoon conditions during monsoon season. The inter-seasonal variability is also evident in radiative forcing (TOA ARE is found to vary in the range -8.06 to -4.33 and -10.4 to -7.25 during summer and winter, respectively). We will discuss relations between MODIS Terra derived AOD, COD and CERES Terra CRF, during various seasons over the northern plains.