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This study presents an original method to evaluate key parameters for theestimation of the direct radiative effect (DRE) of aerosol above clouds: theabsorption of the the cloud albedo. It isbased on multi-angle total and polarized radiances both provided by theA-train satellite instrument POLDER – Polarization and Directionality ofEarth Reflectances. The sensitivities brought by each kind of measurementsare used in a complementary way. Polarization mostly translates scatteringprocesses and is thus used to estimate scattering aerosol opticalthickness and aerosol size. On the other hand, total radiances, togetherwith the scattering properties of aerosols, are used to evaluate theabsorption optical thickness of aerosols and cloud optical thickness. Theretrieval of aerosol and clouds properties (i.e., aerosol and cloud opticalthickness, aerosol single scattering albedo and Ångström exponent) isrestricted to homogeneous and optically thick clouds (cloud optical thicknesslarger than 3). In addition, a procedure has been developed to process theshortwave DRE of aerosols above clouds. Three casestudies have been selected: a case of absorbing biomass burning aerosolsabove clouds over the southeast Atlantic Ocean, a Siberian biomass burningevent and a layer of Saharan dust above clouds off the northwest coast of Africa. Besides these case studies,both algorithms have been applied to the southeast Atlantic Ocean and the results have been averaged during August 2006. Themean DRE is found to be 33.5 W m<sup>−2</sup> (warming).Finally, the effect of the heterogeneity of clouds has been investigated andreveals that it affects mostly the retrieval of the cloud optical thicknessand not greatly the aerosols properties. The homogenous cloud assumption used inboth the properties retrieval and the DRE processing leads to a slightunderestimation of the DRE

Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their direct radiative effect