Previous efforts to use satellite observations to identify and quantify enhancement of cloud albedo due to anthropogenic aerosols have been limited, largely because of strong dependence of albedo on cloud liquid water path (LWP), which is inherently highly variable. We have examined satellite-derived cloud optical properties over a one-week episode for which a chemical transport and transformation model indicates that sulfate aerosol in a remote area of the North Atlantic experienced a substantial excursion due to transport from Northern Europe. Despite the absence of discernible dependence of optical depth or albedo on modeled sulfate loading, examination of the dependence of these quantities on LWP readily permits detection and quantification of increases correlated with sulfate loading which are otherwise masked by variability of LWP, providing unequivocal demonstration on a synoptic scale of brightening of clouds due to the Twomey effect. Examination of the dependence of cloud optical depth and albedo on LWP should be broadly applicable to identification of enhancement by anthropogenic aerosols.
This page was last updated 2002-04-23.
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