Aerosol Enhancement of Cloud Albedo Shown by Satellite Measurements and Chemical Transport Modeling
Schwartz, S.E. (a), Harshvardhan (b), and Benkovitz C.M.(a), Brookhaven National Laboratory (a), Purdue University (b)
Eleventh Atmospheric Radiation Measurement (ARM) Science Team Meeting
The Twomey effect of enhanced cloud droplet concentration, optical depth, and albedo due to anthropogenic aerosols is thought to contribute substantially to radiative forcing of climate change over the industrial period. Present model-based estimates of this indirect forcing are highly uncertain. Increased cloud drop concentration and decreased effective radius indicative of the indirect effect have previously been shown in interhemispheric comparisons of satellite remote sensing data, but efforts to identify and quantify enhancement of cloud albedo due to anthropogenic aerosols in satellite observations have been limited, largely because of strong dependence of albedo on cloud liquid water path (LWP), which is inherently highly variable. Here we examine satellite-derived 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.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
