Satellite remote sensing of aerosol direct radiative forcing over global oceans

The Clouds and the Earth's Radiant Energy System (CERES) instrument on NASA's Terra satellite has been successfully used for examining the impact of clouds and aerosols on the earth-atmosphere system. In aerosol studies, in cloud free conditions, the differences in the CERES reflected shortwave (∼<5m) fluxes without and with the presence of aerosols is a measure of the direct radiative forcing of aerosols (SWARF). However, the CERES instrument does not measure the shortwave fluxes directly and angular distribution models (ADMs) are needed to relate CERES observed radiances to fluxes.; A new empirical method for obtaining the shortwave aerosol ADM from CERES data over cloud-free oceans is developed as functions of near-surface ocean wind speed, Moderate Resolution Imaging SpectroRadiometer (MODIS) aerosol optical depth and the ratio of fine mode to total aerosol optical depth that is an indicator of aerosol type. Results show that a 10% uncertainty will be induced in the derived SWARF values over cloud free oceans if the ADMs are constructed without considering aerosol darkening effect over glint regions or without considering the variations in aerosol properties. Using this new ADM and ten months of observations from the MODIS and CERES, the SWARF is studied over the global oceans. The spatial and seasonal distributions of aerosol optical depth and the independently derived SWARF show a high degree of correlation. The instantaneous top of atmosphere SWARF during the satellite overpass time is -6.4 +/- 2.4 Wm-2. Accounting for sample biases and diurnal averaging we estimate the SWARF over cloud free oceans to be -5.2 +/- 1.2 Wm-2 that is consistent with previous studies. However our study requires no radiative transfer calculations to convert the retrieved aerosol optical thickness to SWARF values and is entirely a measurement-based assessment of aerosol radiative forcing.; Although this study was conducted over the global oceans, we also provide the framework for calculating aerosol radiative forcing over land using three sensors on NASA's Terra satellite using multi-angle, multi-spectral, and broadband CERES measurements. The results from this dissertation suggest that multiple satellite sensors are required to reduce uncertainties in climate forcing studies.