Observations of the first aerosol indirect effect in shallow cumuli

[1] Data from the Cumulus Humilis Aerosol Processing Study (CHAPS) are used to estimate the impact of both aerosol indirect effects and cloud dynamics on the microphysical and optical properties of shallow cumuli observed in the vicinity of Oklahoma City, Oklahoma. Not surprisingly, we find that the amount of light scattered by clouds is dominated by their liquid water content (LWC), which in turn is driven by buoyancy and cloud dynamics. However, removing the effect of cloud dynamics by examining the scattering normalized by LWC shows a statistically significant sensitivity of scattering to pollutant loading (increasing at a rate of 0.002 m2 g−1 ppbv−1). These results suggest that even moderately sized cities, like Oklahoma City, can have a measureable impact on the optical properties of shallow cumuli.