Cloud condensation nuclei and cloud droplet measurements during ACE-2

During the 2nd Aerosol Characterization Experiment (ACE-2), relationships b etween stratocumulus cloud properties and aerosols were examined. Were, the relevant measurements including the cloud condensation nuclei (CCN) activa tion spectrum, updraft velocity, cloud microphysical and aerosol properties are presented. It. is shown that calculations of droplet concentration bas ed on updraft velocity and the CCN activation spectrum are consistent with direct observations. Also discussed is an apparent disparity among measurem ents of the CCN activation spectrum, the accumulation mode size distributio n, and the composition of the submicrometric aerosol. The observed consiste ncy between CCN, updraft and cloud droplets is a necessary refinement; howe ver, extended analyses of the ACE-2 data set are needed to guide improvemen ts in model simulations of the interaction between aerosols and cloud micro physics. In particular, there is need for an examination of aerosol size sp ectra and chemical composition measurements with a view towards validating droplet activation schemes which relate the aerosol and cloud dynamical pro perties to cloud albedo.