Short-wave aerosol radiative efficiency over the global oceans derived from satellite data

Using 5 yr (December 2000.November 2005) of satellite data from the clouds and the earths radiant energy system (CERES) and moderate resolution imaging spectroradiometer (MODIS), we examine the instantaneous short-wave radiative efficiency (E_τ) of aerosols during the morning Terra satellite overpass time over the global oceans (60°N–60°S). We calculate E_τ using two commonly used methods. The first method uses the MODIS aerosol optical thickness (AOT) at 0.55 μm with radiative transfer calculations, whereas the second method utilizes the same AOT values along with a new generation of aerosol angular distribution models to convert the CERES-measured broad-band radiances to fluxes. Over the 5 yr, the global mean instantaneous E_τ between the methods is remarkably consistent and within 5 W m^-2 τ^-1 with a mean value of –70W m^-2 τ^-1. The largest differences between the methods occur in high-latitude regions, primarily in the Southern Hemisphere, where AOT is low. In dust dominated regions, there is an excellent agreement between the methods with differences of <3 W m^-2 τ^-1. These differences are largely due to assumptions in aerosol models and definition of clear sky backgrounds. Independent assessments of aerosol radiative effects from different satellite sensors and methods are extremely valuable and should be used to verify numerical modelling simulations.