Reflectivity variations off the Peru Coast: Evidence for indirect effect of anthropogenic sulfate aerosols on clouds

Using reflectivity measurements from the Total Ozone Mapping Spectrometer ( TOMS), we show that over the months when stratocumulus clouds are prominent off the Peru Coast, the ultraviolet (UV) reflectance of two marine sites i s consistently higher than that of the surroundings. The regions of reflect ivity enhancement coincide with large anthropogenic sulfate aerosol emissio n sources, and the magnitude of the enhancement has a strong seasonal depen dence that is related to the seasonal cloud movement. We propose the indire ct aerosol effect as a plausible explanation for the reflectivity observati ons.