PHYSICOCHEMICAL MEASUREMENTS TO INVESTIGATE REGIONAL CLOUD CLIMATE FEEDBACK MECHANISMS

On a regional scale, cloud-climate feedback mechanisms are investigate d by analyzing the impact of anthropogenic sulfur emissions on the mic rostructure and short-wave albedo of clouds formed at a mountain-top l ocation and simultaneously observing these clouds by AVHRR (Advance Ve ry High Resolution Radiometer) aboard the NOAA (National Oceanographic and Atmospheric Administration) satellites. Cloud droplet number conc entrations (CDNC) and ionic composition of cloud water are measured in situ along with meteorological parameters. The thickness of the overl ying clouds and the 48 h back-trajectories of air masses are determine d from on site measurements and Hybrid Single Particle Lagrangian Inte grated Trajectory (HY-SPLIT) model. In general, more acidic clouds wer e found to have smaller effective radii of droplets but larger CDNC. T he short-wave albedo of clouds determined from in situ measurements de creased with an increase in the cloud water pH which was largely affec ted by the sulfate concentration in the cloud forming air mass. For si x coincidental cloud events, the AVHRR retrieved cloud albedo (channel 1, wavelength = 0.63 mu m) agreed well with those determined from in situ microphysical measurements, the correlation coefficient being 0.9 5. These findings indicate that the sulfate contents of air masses are capable of influencing cloud-climate feedback mechanisms by changing the albedo of thin, continental clouds.